IGCSE Environmental Management Topic 2: Land

2.1 Soils & Crop Growth 2.2 Food Production & Crop Yield 2.3 Soil Erosion

Hi Tara. Topic 2 has only three sub-topics, which makes it look small on the syllabus page. It is not. 2.2 alone has twelve lettered strategies for increasing food production and nine lettered impacts of doing it badly, and 2.3 has another fifteen items across causes, impacts and strategies. So treat this topic as three long sections rather than three quick ones.

The good news is that the three sub-topics chain together, and once you see the chain you can stop learning them as three separate lists. 2.1 is what soil is and what makes it grow crops. 2.2 is what farmers do to grow more, and what goes wrong when it is done unsustainably. 2.3 is the single worst thing that goes wrong — soil erosion — taken through its causes, its impacts and the strategies that fix it. Notice that the last item of 2.2.4 is “soil erosion” and the first item of 2.3.1 is “unsustainable agricultural practices”. The syllabus is deliberately handing you the join. Learn it as cause → impact → strategy, because that is exactly the shape of a six-mark question.

One warning about tone, and it matters for your marks. This topic makes it very easy to write an answer that says intensive farming is bad, monocultures are bad, fertilisers are bad and pesticides are bad. That answer will not score well, and not because the examiner disagrees with you — because it is only half of the question. Intensive agriculture and monoculture exist because they produce far more food per hectare, and food shortage is also an environmental and social problem. The syllabus wants the trade-off: what a practice achieves, what it costs, who bears that cost, and over what timescale. Every table in this guide has two columns for that reason.

Two definitions are given word for word and can be asked back word for word: weather (2.1.4) and sustainable food production (2.2.2). They are boxed in yellow. There is also a definition of genetically modified organisms embedded in 2.2.3(d) that is worth learning in the syllabus's own words. Start with those three sentences.

The command word tells you what to write — read it before you read the question

Almost every mark lost on a question you knew is lost here: the paper says state and the candidate writes a paragraph, or it says explain and the candidate writes a list. Cambridge uses these words with fixed meanings, and Paper 2 in particular opens with the short ones because it is a source-led paper — it wants you to read the figure first and theorise afterwards.

Command word	What it is asking for, and how long the answer should be
State	Give a short fact or a single value. No reason, no sentence needed. “State the month with the highest rainfall” → January. One or two words is a complete answer, and adding more wastes time you need later.
Identify	Pick something out of a source you have been given — a figure, a table, a map, a photograph. It is the standard opener on a source-led question. The answer is in the source, so do not answer it from memory; find it and quote it, with its unit if it has one.
Calculate	Work out a number, and show the working, because the method usually carries a mark of its own. Give the unit and do not round more than the data justifies. Percentage change is (change ÷ original) × 100; “original” means the value you started from, which is the one candidates get wrong.
Describe	Say what is happening or what something is like, without saying why. Describing a trend means: overall direction, then any change of direction, then figures from the source to support it — a described trend with no numbers in it rarely gets full marks.
Explain	Give the reason or the mechanism. Every sentence needs a because or a so in it. If your answer would still make sense with all the connectives removed, you have described rather than explained.
Suggest	Apply what you know to a situation you have not met before. There is no single learned answer; the examiner wants sensible reasoning that fits the context in front of you. This is the AO3 skill itself, and it is why the source matters more than your notes.
Compare	Write about both things in the same sentence, using comparative words: higher than, faster than, whereas. Two separate descriptions, one per paragraph, is not a comparison and is marked as if the second half is missing.
Discuss the benefits and limitations	Both columns, whether or not you think one side wins. This is the shape of the six-mark question in this topic, and half the marks sit in the column candidates leave out.
Evaluate	Go one step past discuss: weigh the two sides and reach a judgement, then say what your judgement depends on. “Terracing is the more effective strategy on a steep slope because it removes the gradient the water runs down, but only where there is enough labour to build and maintain it; on gentle slopes contour ploughing achieves most of the benefit for almost no cost.” An evaluation with no conclusion in it loses the marks that separate it from a discussion.

One habit worth building now. Underline the command word and the mark allocation before you write anything. Six marks means roughly six creditable points, and on a discuss or evaluate question it means points on both sides.

2.1 Soils and Crop Growth ▼

▶ Watch: Soil, Nutrients and What Limits Photosynthesis

Links only, opening on YouTube in a new tab — nothing loads from Google while you are on this page. Be clear about what these are: two of the seven are made for IGCSE 0680 (Mr Mathew and Dr Mohamed Saber, both using the older chapter numbering, so their “Chapter 3” is this topic). The other five are general science — useful for the mechanism, but they were not made against this syllabus and will go beyond it in places. Nothing here is a substitute for 2.1.4 and 2.1.5, which are two short statements you simply learn. The syllabus decides what is in scope, not a video. Watch one, then come back and do the checkpoint questions — watching without testing yourself feels like learning but is not.

2.1.1 What soil is made of

Soil is not dirt and it is not simply crushed rock. It is a mixture of four components, and every one of them has to be there for a crop to grow. The syllabus lists them in this order, and a “describe the composition of soil” question expects all four.

Component	What it consists of
(a) Mineral particles	Sand, silt and clay — fragments of weathered rock, differing in size. Sand particles are the largest, silt is intermediate, clay is the smallest. This is the mineral skeleton of the soil and it comes from the rock beneath, by the weathering you met in Topic 1.
(b) Organic content	Two things, and the syllabus wants both. First, living organisms: plants, animals, fungi and bacteria — roots, earthworms, insects, and the decomposers. Second, organic matter from decomposition — the partly broken down remains of dead plants and animals, often called humus.
(c) Gases	Air in the pore spaces between the particles. Roots and soil organisms respire and need oxygen; a soil with no air in it is a soil in which roots die.
(d) Water	Water held in and around the pore spaces, carrying dissolved mineral ions. This is the only way a root can take up nutrients — they must be in solution.

What you are not asked

The syllabus states plainly that you do not need to know what proportion of a soil is mineral, organic, air or water. So do not try to memorise those figures and do not quote them in an answer. You need the four components and what each one does. Anything more is time spent on something that cannot be asked.

Four components, one hook

Rock, life, air, water. Mineral particles (rock), organic content (life, living and dead), gases (air), water. If you can say those four words you can build the whole answer out from them, and each one leads straight into a reason it matters for crop growth.

2.1.2 Why the composition matters for crop growth

This is the objective that turns the list above into marks. Each component is here again, but now with the word because attached.

Feature of the soil	Why it matters for a crop
(a) Mineral particles: sand, silt and clay	Particle size controls almost everything else. Sand particles are large, so the gaps between them are large: water drains through quickly, the soil is well aerated and easy to work, but it dries out fast and nutrients are washed away with the water. Clay particles are tiny and flat, so the gaps are tiny: water is held tightly and nutrients are retained, but the soil drains poorly, becomes waterlogged, holds little air and is heavy to cultivate. Silt is intermediate on every count. A crop needs the balance between these, which is what 2.1.3 is about.
(b) Nutrient content	Plants need mineral ions dissolved in soil water, supplied both by the organic content as it decomposes and as inorganic ions already in the soil. The three the syllabus names are nitrogen as nitrate ions, NO₃⁻, needed for amino acids and proteins and so for leaf growth; phosphorus as phosphate ions, PO₄³⁻, needed for root development and energy transfer; and potassium as potassium ions, K⁺, needed for flowering, fruiting and general regulation inside the plant. Shortage of any one limits yield however good the rest of the soil is.
(c) pH: acidic, neutral and alkaline	pH controls how available the mineral ions are: at the wrong pH, ions become locked into forms the roots cannot absorb, so a soil can be full of nutrients the crop cannot reach. It also affects the soil organisms and the decomposers. Most crops do best at a roughly neutral pH, and farmers add lime to raise the pH of an acidic soil.
(d) Pore spaces	The gaps between particles are where the air and water sit, and where roots grow through. Too few pore spaces — a compacted or heavy clay soil — and roots cannot penetrate, water cannot drain and air cannot reach the roots. Too many large pores and everything drains straight through.
(e) Gas content	Roots respire, and so do the soil bacteria and fungi that release nutrients from organic matter. Respiration needs oxygen. In a waterlogged soil the pore spaces fill with water, oxygen is excluded, root respiration fails and the roots die — which is why drainage is a farming problem and not just a comfort.
(f) Water content and drainage	Water is needed as a raw material for photosynthesis, to keep cells turgid so the plant stays upright, and as the solvent that carries mineral ions into the root. But the soil must also drain: standing water excludes air. A crop needs a soil that holds enough water to survive a dry spell and lets the excess go.
(g) Ease of cultivation	The farmer has to plough, sow, weed and harvest. A heavy wet clay is difficult and slow to work and can only be worked in a narrow window of weather; a light sandy soil is easy but blows and washes away. Ease of cultivation is an economic factor as much as a biological one — it decides labour, fuel and machinery costs.

Sand, silt, clay and loam. The particles are drawn to show relative size and the pore spaces between them, not to any scale of quantity.

2.1.3 Why loam is the best medium for crop growth

Loam is a soil containing a mixture of sand, silt and clay together with organic matter. The exam question is almost always explain why it is a good growing medium, and the syllabus gives you five reasons. Learn them as five, because a 5-mark question is a real possibility.

Reason	The mechanism
(a) Ideal combination of mineral particles and pore spaces	The mixture of large sand grains and small clay particles produces a range of pore sizes: large pores that let air in and excess water out, and small pores that hold water against gravity. Neither a pure sand nor a pure clay can do both.
(b) Retains moisture	The clay and the organic matter hold water in the small pores, so the crop has a supply through dry spells and does not wilt after a few days without rain.
(c) Contains organic content and inorganic ions	Decomposing organic matter releases nitrate, phosphate and potassium ions steadily into the soil water, so nutrients are supplied continuously rather than in a single dose, and the soil holds on to them.
(d) Allows excess water to drain	The large pores let surplus water pass through, so the soil does not become waterlogged, air can reach the roots and root respiration continues.
(e) Easy to cultivate	Loam is neither as heavy and sticky as clay nor as loose as sand, so it can be ploughed and sown over a wider range of weather, with less fuel, machinery wear and labour.

Loam in one sentence

“Loam holds enough water and nutrients to feed the crop, but drains and aerates enough not to drown it — and it is easy to plough.” That single sentence contains four of the five marks. Add “because it mixes large sand pores with small clay pores” and you have the fifth.

2.1.4 Weather — a definition to learn word for word

Learn this exactly

Weather is the day-to-day conditions of the atmosphere in a location.

Three parts: day-to-day, conditions of the atmosphere, in a location. The reason the syllabus is fussy is that weather has a partner definition — climate, which you meet in Topic 4 — and the difference between them is timescale. Weather is what it is doing today; climate is the pattern over many years. Candidates lose the mark by writing one and being asked for the other.

2.1.5 Wet seasons and dry seasons

This is a short, stated objective: some areas of the world experience wet seasons and dry seasons that impact crop growth. You do not need a mechanism for why monsoons happen — you need to be able to say what a strongly seasonal rainfall pattern does to farming.

In the wet season there is plenty of water for growth, but heavy rain also causes flooding, waterlogged soil in which roots cannot respire, leaching of nutrients out of the soil, and erosion of bare ground. In the dry season crops may fail for lack of water, soil dries and cracks, and bare dry soil is blown away by wind. The practical effect is that the growing season is limited to part of the year, so the timing of planting matters enormously, and a wet season that arrives late or fails can lose an entire harvest. It is also the reason irrigation, rainwater harvesting and mulching matter so much in 2.2.3.

2.1.6 Conditions for the optimum rate of photosynthesis and crop growth

A crop's yield depends on how much photosynthesis it can do over the season, and the syllabus asks you to describe and interpret the conditions for that — interpret meaning you may be given climate data for two places and asked which will produce more.

carbon dioxide + water → glucose + oxygen

in the presence of light energy, absorbed by chlorophyll

Condition	What it means, and how it limits yield
(a) Length of growing season	The period of the year when temperature, water and light are all sufficient for a crop to grow. A long growing season means more total photosynthesis, a larger yield, and possibly more than one harvest from the same land in a year. A short season, whether limited by cold winters or by a short wet season, caps the yield however good the soil is.
(b) Optimum weather conditions	Chiefly temperature and rainfall. Photosynthesis and growth speed up as temperature rises to an optimum, because the enzymes controlling them work faster; above that optimum the rate falls again, because the enzymes are denatured — damaged so that they no longer work. (0680 wants the shape of that curve, a rise to an optimum and then a fall; the biochemistry behind it belongs to Biology and is background here.) Very high temperatures also cause water loss and wilting. Too little rainfall and the crop cannot photosynthesise or stay turgid; too much and the soil waterlogs and nutrients leach away. Wind, frost, hail and storms all damage crops directly.
(c) Daylight hours	Light supplies the energy for photosynthesis, so more hours of daylight means more hours of photosynthesis per day and a greater yield. Day length varies with latitude and season: near the equator it is roughly constant all year, while at high latitudes summer days are long and winter days very short, which is one reason growing seasons are short there. Cloud cover reduces light intensity even when the day is long.

Interpret means use the numbers you are given

If a question gives you a table of monthly temperature and rainfall for two locations and asks which is better for growing maize, do not answer from general knowledge. Quote the figures. “Location A has six months above 20 °C with more than 60 mm of rain, while location B has only three, so A has the longer growing season and will give the higher yield.” The marks are for reading the data and linking it to a mechanism, not for knowing about maize.

Worked example A farmer's field has a heavy clay soil. Crops grow poorly and the field is often waterlogged after rain. Explain why the yield is low, and suggest one way the soil could be improved. [5]

Step 1 — start from particle size, because everything follows from it

Clay particles are very small and flat, so the pore spaces between them are very small. Water cannot drain through them easily, so it stays in the soil after rain.

Step 2 — the mechanism that costs the yield

Because the pore spaces are full of water, there is very little air in the soil, so oxygen is not available to the roots. Root cells cannot respire properly, so they have no energy to take up mineral ions from the soil water, and eventually the roots die. Growth slows and yield falls. (Biology calls that uptake active transport; 0680 does not ask for the term, so “roots need oxygen in order to take up nutrients” is the level to write at.)

Step 3 — the second reason, which many candidates miss

A heavy wet clay is also difficult to cultivate: the farmer can only plough it in a narrow window of dry weather, which delays sowing and shortens the growing season.

Step 4 — the improvement

Add organic matter such as manure or compost. It binds the fine clay particles into larger crumbs, which creates larger pore spaces, so the soil drains better and holds more air, while still retaining moisture and adding nutrients. (Installing field drains, or adding sand, would also be creditable.)

Small particles → small pores → poor drainage → no oxygen → roots cannot respire → low yield. Fix: organic matter to improve structure.

Source-led question · AO3

Table 1 — which location grows the better maize crop?

This is the question the exam tip above describes, with the table attached. Objective 2.1.6 says describe and interpret conditions suitable for crop growth, and interpreting means working from figures you are handed rather than from what you already know about maize. Maize needs warmth and water together: as a working rule for this question, a month counts towards the growing season if the mean temperature is above 20 °C and rainfall is more than 60 mm.

Location	J	F	M	A	M	J	J	A	S	O	N	D
A — mean temperature / °C	24	25	26	26	25	23	22	23	25	26	25	24
A — rainfall / mm	210	195	175	120	45	10	5	8	30	55	160	200
B — mean temperature / °C	9	11	15	19	19	24	26	25	23	18	14	10
B — rainfall / mm	30	35	55	70	90	120	140	130	55	45	40	32

Table 1. Mean monthly temperature and rainfall at two locations. These figures are constructed for practice, not measurements from a named weather station — but they behave the way real records do. Location A is in the southern-hemisphere tropics, Location B in the northern-hemisphere warm temperate zone, which is why their wet months fall at opposite ends of the year.

Statethe month with the highest rainfall at Location A.[1]

Describethe pattern of rainfall through the year at Location B, using figures from the table.[3]

Calculatehow much more rain falls in a year at Location A than at Location B, and express that as a percentage of the Location B total. Show your working.[3]

Explainwhy Location B has a shorter growing season than Location A, even though both have months warm enough for maize.[4]

Suggestwhich location will give the higher maize yield from one planting, and justify your answer with figures from Table 1.[4]

Write your answers out before you open the mark scheme. Reading a model answer you have not attempted feels like learning and is not.

Source question 1 — identify

Look at Table 1. Which month has the lowest rainfall at Location A, and how much rain falls in it?

A April, with 120 mm, the last month of the wet season

B June, with 10 mm, when the mean temperature is 23 °C

C July, with 5 mm, when the mean temperature is 22 °C

D September, with 30 mm, as the rain starts to return

July, at 5 mm. This is an identify part: the answer is in the table, so find the smallest number in the Location A rainfall row rather than reasoning about seasons. June is close at 10 mm and August at 8 mm, which is exactly why you read the row rather than guess the middle of the dry season. Notice also that the driest months at A are its coolest, so A is in the southern hemisphere.

Source question 2 — calculate

Location A receives 1213 mm of rain in the year. Using Table 1, what is the total annual rainfall at Location B?

A 794 mm

B 842 mm

C 886 mm

D 928 mm

Adding the twelve figures in the Location B rainfall row gives 842 mm. Add them in pairs from each end — it halves the chances of a slip and you can check the running total. A is therefore 371 mm wetter, which is 44 per cent more than B receives, but notice that the annual total is the least useful figure in the table: what decides the crop is when the rain falls, not how much of it there is.

Model answer The five parts above, worked in full. [15]

State — one word is a complete answer

January, with 210 mm. Do not write a sentence about it; the mark is for the reading.

Describe the pattern — direction, then turning points, then figures

Rainfall at Location B is lowest in the northern winter, at 30 mm in January, and rises through the spring to a peak of 140 mm in July, before falling again to 32 mm in December. So the rain falls mainly in the middle of the year, in the same months as the highest temperatures. Three things earn the three marks: the overall shape, the position of the peak, and figures quoted for both.

Calculate — show the working, then the unit

Location A total = 1213 mm. Location B total = 842 mm. Difference = 1213 − 842 = 371 mm.
As a percentage of the Location B total: (371 ÷ 842) × 100 = 44.1 per cent, which is about 44 per cent more. The trap is dividing by the Location A total instead; “more than B” means B is the value you started from.

Explain — the mechanism, with a because in every sentence

A month is only useful to the crop when temperature and water are sufficient at the same time. At Location B the warmest months are also the wettest, but the warm season itself is short: temperature is above 20 °C in only 4 months of the year, because B lies far enough from the equator to have a cold winter, and day length is short in those winter months as well. Below that temperature the enzymes controlling photosynthesis work slowly, so the crop grows little even when there is water. At Location A the temperature never falls below 22 °C, so temperature never ends the season — it is ended by the dry months instead, when rainfall drops to 5 mm.

Suggest — commit to an answer, then justify it with the numbers

Location A. Counting months above 20 °C with more than 60 mm of rain, A has 6 such months (January, February, March, April, November, December) while B has only 3 (June, July, August). A therefore offers a growing season roughly twice as long, so the crop can photosynthesise for longer before harvest and yield more; A is also warmer throughout, with a mean of 24.5 °C against 17.75 °C, so growth is faster while the season lasts. The marks are for reading the data and linking it to a mechanism, not for knowing anything about maize.

The sentence that lifts the answer

Say what the data cannot tell you. Table 1 gives means, and a mean hides the year that failed — a location whose rain arrives reliably every year is worth more to a farmer than one with the same average and a wet season that sometimes does not come. Nor does the table say anything about the soil, and a long warm wet season on a thin eroded soil still gives a poor yield.

A: 6 growing months against B's 3, from the same rule applied to both rows. Quote the rule, quote the counts, quote at least two figures.

Checkpoint 2.1

Answer, then read the explanation even when you were right.

Your Score 0 / 14

Question 1

Which list gives the four components of soil named by the syllabus?

A sand, silt, clay and stones of various different sizes

B nitrate ions, phosphate ions, potassium ions and humus

C mineral particles, organic content, gases and water

D bedrock, subsoil, topsoil and the surface leaf litter

The four components are mineral particles, organic content, gases and water, and an answer that misses the air or the water is incomplete. A lists only the mineral fraction, which is one component out of four. B lists nutrients found within the soil rather than the components of it. D describes the layers of a soil profile, which is a different idea altogether.

Question 2

Which is included in the organic content of a soil?

A the dissolved nitrate and phosphate ions in soil water

B the smallest of the mineral particles, which are the clay

C living fungi and bacteria, and matter from decomposition

D the air held in the pore spaces between soil particles

Organic content covers both the living organisms — plants, animals, fungi and bacteria — and the organic matter left from decomposition, and the syllabus asks for both halves. A names inorganic ions, which are a separate feature. B is a mineral particle, not organic. D is the gas component, listed separately.

Question 3

Why does a sandy soil lose nutrients quickly?

A large pore spaces let water drain through, carrying ions with it

B sand particles chemically react with nitrate and phosphate ions

C sandy soils contain no decomposers to release ions from matter

D the low pH of sandy soil locks the ions into insoluble forms

Mineral ions are dissolved in the soil water, so water that drains rapidly through wide pores takes the nutrients down and out of reach of the roots. B invents a chemical reaction. C is too absolute — decomposers live in sandy soils too, just with less organic matter to work on. D describes a real pH effect, but that locks nutrients in place rather than washing them away.

Question 4

A plant is short and its older leaves are yellow. Which ion is the plant most likely to be short of?

A potassium ions, K⁺, which the plant needs for flowering

B nitrate ions, NO₃⁻, which supply nitrogen for proteins

C phosphate ions, PO₄³⁻, which are needed for root growth

D carbonate ions, which the plant uses to build its cell walls

Nitrogen is taken up as nitrate and used to make amino acids and proteins, so a shortage stunts growth and yellows the leaves. Potassium shortage shows mainly in poor flowering and fruiting, and phosphate shortage in poor root development, so neither fits the symptoms as well. Carbonate ions are not one of the three the syllabus names, and cell walls are built from carbohydrate.

Question 5

Why do roots die in a waterlogged soil?

A the roots take in so much water that the root cells burst open

B water fills the pore spaces, so no oxygen reaches the roots

C the water washes all of the mineral ions away from the root hairs

D waterlogged soil is always far too acidic for roots to survive in

Air and water compete for the same pore spaces, so a saturated soil has no oxygen and root cells cannot respire aerobically. A misapplies osmosis to a whole root. C describes leaching, which is a genuine effect of heavy rain but not the reason roots die. D asserts a pH change that does not automatically follow from waterlogging.

Question 6

Which best explains why loam is a good medium for crop growth?

A it has a range of pore sizes, so it holds water and still drains well

B it contains no clay at all, so surplus water always drains away fast

C it is made almost entirely of clay, so it holds a great deal of water

D it contains no organic matter, so no nutrients are ever washed out

The point of loam is that it does two opposite jobs at once, because a mixture of particle sizes gives both small pores that retain water and large ones that drain and aerate. C describes a heavy clay, which waterlogs. B describes a sand, which dries out and loses nutrients. D gets it backwards — organic matter is one of the reasons loam is fertile.

Question 7

Which definition of weather matches the syllabus wording?

A the average atmospheric conditions over a period of many years

B the seasonal pattern of wet and dry periods within a region

C the total rainfall and the mean temperature over a whole year

D the day-to-day conditions of the atmosphere in a location

Weather is short-term and local, and the syllabus wording is exactly that. A is the definition of climate, which is the partner term and the one candidates most often substitute by mistake. C describes annual climate data. B describes a seasonal pattern, which again is climate rather than weather.

Question 8

Two regions have the same soil and rainfall, but one has a growing season of ten months and the other four. Why does the first produce a higher annual yield?

A its soil holds a larger quantity of nitrate and phosphate ions

B more days on which photosynthesis and growth can take place

C its crops photosynthesise at a faster rate on each individual day

D a longer season means the soil is ploughed more times each year

Growing-season length works by multiplying the number of days of growth, and it may also allow more than one harvest from the same land. A is ruled out by the question, which says the soils are the same. C confuses total yield with daily rate; the rate could be identical. D notices a real consequence but ploughing more often does not itself raise yield.

Question 9

Why does the rate of photosynthesis fall if the temperature rises well above the optimum?

A the enzymes controlling the reactions are denatured by the heat

B light of the wavelengths chlorophyll uses is no longer available

C the plant stops respiring, so it has no energy left for growth

D carbon dioxide becomes less soluble, so none can reach the leaf

Photosynthesis is enzyme-controlled, so the rate rises with temperature to an optimum and then falls as the enzymes are denatured. D confuses a gas-solubility fact with the mechanism. B changes the light rather than the temperature. C reverses what happens to respiration, which speeds up rather than stopping.

Question 10

A region has a pronounced dry season. Which effect on crop growth is most likely?

A nutrients are leached downwards out of reach of the crop roots

B soils become waterlogged so the roots are unable to respire

C the crop grows faster because there is more sunlight available

D the growing season is shortened because water becomes limiting

Without water the crop cannot photosynthesise or stay turgid, so growth stops and the usable season is confined to the wet months. A and B are both real, but they are effects of the wet season, not the dry one. C takes a true fact about clear skies and draws the wrong conclusion, because water, not light, is the limiting factor here.

Question 11

A crop is grown where the summer days are long. Why do the longer daylight hours increase its growth?

A more hours of photosynthesis each day, so more growth

B warmer nights, so the crop respires less in the dark

C stronger wind by day, so more carbon dioxide reaches it

D less cloud by day, so rainfall is spread more evenly

Light supplies the energy for photosynthesis, so more hours of light means more hours of photosynthesis and a greater yield — the mechanism 2.1.6(c) wants. Warmer nights, wind and cloud are real effects of weather, but none of them is what day length does. (Long days only help while the temperature allows growth, which is why a short northern summer still limits the crop.)

Question 12

A field of crops grows badly and the soil is found to be strongly acidic. Fertiliser has been applied, so the nutrients are present. What is the most likely reason for the poor growth?

A the pore spaces close up, so the soil can hold no air

B some mineral ions become unavailable to the roots

C clay particles turn into silt, so the texture changes

D the soil holds much more water than the crop can use

pH is one of the seven features in 2.1.2, and it works indirectly: the nutrients can be in the soil and still not reach the plant, because at a strongly acidic or strongly alkaline pH some mineral ions are held in forms the roots cannot take up, and the soil organisms that release nutrients from organic matter also work poorly. Most crops do best near neutral, which is why farmers add lime to an acidic soil. A and D describe drainage and pore space, which are separate features. C is not something pH can do — particle size comes from the parent rock.

2.2 Food Production and Crop Yield ▼

▶ Watch: Types of Farming, GM Crops, Fertilisers and Pest Control

Links only, opening on YouTube in a new tab. Two are 0680-specific; the rest are general science or GCSE Geography and overlap rather than match. Be aware of what is missing. 2.2.3 has twelve lettered strategies and this list covers roughly half of them: there is no dedicated video here for improved irrigation, controlled environments (greenhouses, hydroponics, aeroponics), managed grazing, urban farming or agroforestry. Those five are taught in the table above and tested in the checkpoint, and the guide is your source for them. Do not read a video list as a coverage map.

2.2.1 The types of agriculture

Four pairs or groups of terms, and they are classifications on different axes — a single farm can be described by several of them at once. A commercial arable monoculture is all three things simultaneously, and being able to say so is the sign that you have understood the classification rather than memorised it.

Type	What it means
(a) Arable, pastoral and mixed	Arable farming grows crops. Pastoral farming raises livestock, usually on grass. Mixed farming does both on the same farm, which lets the manure from the animals fertilise the crops and the crop residues feed the animals. That circularity is why mixed farming keeps appearing in the sustainability answers later on.
(b) Subsistence and commercial	Subsistence farming produces food mainly to feed the farmer and the family, with little or no surplus to sell. It is usually small-scale, labour-intensive and low-input. Commercial farming produces food to sell for profit, is usually larger, more mechanised and higher-input, and is oriented to whatever the market will buy.
(c) Intensive	A high input of labour, machinery, fertiliser, pesticide, irrigation or feed per unit area, in order to obtain a high yield from a small area of land. It can be either commercial or subsistence: rice paddies worked by hand and a glasshouse tomato operation are both intensive.
(d) Monoculture	Growing a single crop species over a large area, often year after year on the same land. It allows the whole farm to be planted, treated and harvested with one set of specialised machinery at one time, which is highly efficient and cuts costs per tonne.

Do not turn a classification into a judgement

“Intensive” and “monoculture” are descriptions of how a farm operates, not verdicts on it. Intensive farming produces much more food per hectare, which means less land has to be farmed in total to feed a given population, and that can leave more land as natural habitat. Monoculture lowers the cost of food, which matters most to the people with the least money. Both also carry real costs, which is the whole of 2.2.4. An examiner is looking for you to hold both facts at once; an answer that only attacks them is marked as incomplete, not as principled.

2.2.2 Sustainable food production — a definition to learn word for word

Learn this exactly

Sustainable food production is the production of sufficient food for the present generation using methods that ensure future generations can grow food from the same land.

Notice the first half: sufficient food for the present generation. Sustainability in this syllabus never means growing less food. It means growing enough, by methods that leave the land able to do it again. If your answer to a sustainability question is “farm less intensively” without saying how the food is still produced, you have only answered the second half.

2.2.3 Twelve strategies to increase food production and crop yield

This is the longest list in the topic. Read the command word: describe and explain, so each strategy needs a mechanism, not just a name. The table gives you the mechanism and, where it matters, the cost — because several of these strategies reappear in 2.2.4 as the things that cause harm when overused.

Strategy	How it raises yield — the mechanism
(a) Mixed cropping, intercropping and crop rotation	Mixed cropping grows more than one crop in the same field, so that if one fails the other still yields. Intercropping grows two crops in alternating rows, so the ground is covered, weeds are suppressed and light and water are used more fully. Crop rotation grows different crops on a field in successive years: different crops take up different ions in different proportions, so no single nutrient is stripped out, and pests and diseases specific to one crop cannot build up in the soil. Including a legume in the rotation restores nitrogen to the soil naturally.
(b) Improved methods of irrigation	Trickle or drip irrigation delivers water through pipes directly to the base of each plant, so almost none is lost to evaporation or to the ground between plants; it also keeps the soil from being saturated, which reduces salinisation and waterlogging. Rainwater harvesting collects and stores rain from roofs and surfaces during the wet season for use in the dry one. Automated watering systems use timers and soil-moisture sensors to apply exactly the amount of water needed, when it is needed, so less is wasted and the crop is never short.
(c) Mechanisation	Tractors, seed drills, sprayers and combine harvesters allow a much larger area to be worked by fewer people and much faster, so sowing and harvesting happen at the optimum time rather than being spread over weeks. Machines also apply seed, water and chemicals more evenly and precisely than hand labour. The costs are the purchase price, the fuel, the loss of agricultural employment, and soil compaction under heavy machinery.
(d) Genetically modified organisms	The syllabus defines this as changing the genetic material of an organism by removing, changing or inserting individual genes to give favourable characteristics. Crops can be given resistance to particular pests or diseases, tolerance of drought or salt, tolerance of a specific herbicide, faster growth, or improved nutritional content. Yields rise and losses fall, and pesticide use may drop where a crop is pest-resistant. Against that: seed is usually more expensive and often has to be bought each season, small farmers may become dependent on one supplier, pests can evolve resistance, there are concerns about effects on non-target organisms and about gene transfer to wild relatives, and public acceptance and regulation vary widely between countries.
(e) Controlled environments	Greenhouses let the farmer control temperature, humidity, light and carbon dioxide concentration, so the crop grows at close to its optimum rate all year and the growing season is extended. Hydroponics grows plants with their roots in a nutrient solution rather than soil, so the exact ions needed are supplied and no soil-borne pests are present. Aeroponics suspends the roots in air and sprays them with nutrient solution, which uses even less water. All three give very high yields per unit area and allow production where the soil or climate is unsuitable, at the cost of high energy use and high set-up cost.
(f) Managed grazing: livestock rotation	Animals are moved between fenced areas on a planned cycle instead of grazing one area continuously. Each area is grazed hard for a short period and then rested, so the grass recovers and regrows, the roots stay strong, vegetation cover is maintained and the soil is not laid bare. It also breaks the life cycle of parasites and spreads manure evenly. The result is more grass grown per hectare and less overgrazing.
(g) Urban farming	Growing food within towns and cities — on rooftops, in allotments, in vertical farms and on unused land. Food is produced close to where it is eaten, so transport, cost and spoilage fall, and land with no agricultural alternative is brought into production. It also improves access to fresh food in cities. The area available is small, so it supplements rather than replaces rural agriculture, and urban soil may need testing for contamination.
(h) Agroforestry	Growing trees and crops (or livestock) together on the same land. The trees provide shade and shelter, reduce wind speed and so reduce erosion, their roots bind the soil and draw water and nutrients from deeper layers, and their fallen leaves add organic matter. They also yield a second product — fruit, nuts, timber or fodder — so the farmer has more than one source of income. The crop yield per hectare may be somewhat lower than in a cleared field, but the total output and the long-term soil condition are better.
(i) Inorganic NPK fertilisers	Manufactured fertilisers supplying nitrogen, phosphorus and potassium as soluble ions. Because the ions are already dissolved or dissolve quickly, they are available to the roots immediately, the exact quantity of each can be applied, and the effect on yield is large and fast. They are the single biggest reason world crop yields rose in the twentieth century. Their limitations are the energy and cost of manufacture, the fact that they add no organic matter so soil structure is not improved, and the leaching and eutrophication that follow overuse.
(j) Organic fertilisers	Crop residue (the stems and leaves left after harvest), manure and mulch (a layer of organic material spread on the surface). They release nutrients slowly as they decompose, so less is leached; they add organic matter, which improves soil structure, water retention and the population of soil organisms; and mulch additionally shades the soil, holds moisture in and suppresses weeds. They are often free or cheap on a mixed farm. Against that, the nutrient content is lower, less predictable and released more slowly, so large quantities must be spread, and the effect on yield in a single season is smaller.
(k) Chemical control of pests	Pesticides kill the organisms that reduce yield: insecticides for insect pests, herbicides for weeds competing for light, water and nutrients, and fungicides for fungal diseases. They act quickly, work over large areas, are relatively cheap, and can save a crop that is already under attack. Their limitations are that pests evolve resistance, that non-target organisms including pollinators and the pests' own predators are killed, and that residues can run off into water or persist along a food chain.
(l) Biological control of pests	Introducing or encouraging a natural predator, parasite or pathogen of the pest, so that the pest population is reduced without chemicals. It is specific to the target species, so pollinators and other organisms are not harmed; it does not leave residues; and once established it can be self-sustaining and costs little to maintain. Against that, it is slow to take effect, it reduces the pest rather than eliminating it, it does not help in an emergency, and an introduced control organism can itself become a problem if it has no predators in the new area — so it has to be researched carefully first.

Grouping the twelve

Learn them in four groups rather than as a list of twelve: how you arrange the land (mixed cropping and rotation, managed grazing, agroforestry, urban farming), what you add (inorganic fertilisers, organic fertilisers, irrigation), what you control (chemical pest control, biological pest control, controlled environments), and what you change about the crop or the work (genetically modified organisms, mechanisation). Four groups you can recall under pressure will get you to the item you need.

Chemical versus biological control is a classic compare question

The mark scheme wants speed against persistence. Chemical: fast, broad, cheap, but resistance develops, non-target organisms are killed and residues spread. Biological: specific, no residues, self-sustaining, but slow, incomplete, and risky if the control organism spreads. Note that neither is simply better — the honest answer is that biological control suits a long-term programme and chemical control suits an outbreak, which is why many farms use both.

2.2.4 The impacts of unsustainable agricultural practices

Every item in this list is what happens when something in 2.2.3 is pushed too far. That is the way to hold it: the practice is not the problem, the over is. And each impact has a mechanism, because the command word is again describe and explain.

Impact	The mechanism, and who it affects
(a) Overproduction of food: food wastage	Producing more than is eaten means that the land, water, fertiliser, fuel and labour used to grow the wasted portion are spent for nothing, and the food decomposes in landfill releasing methane. Waste happens at every stage: in the field when prices are too low to harvest, in storage and transport where refrigeration is poor, and in shops and homes. Reducing waste raises the food available without farming any more land at all, which is why it is listed first.
(b) Food shortages: cash crops and biofuel crops replacing food crops	Land is used to grow cash crops — coffee, cotton, soya beans, palm oil — or biofuel crops, because these earn more than staple food. The farmer's income rises and the country earns foreign currency, which is a genuine benefit. But less land grows food, so local food supply falls and prices rise, and the people who suffer are those who buy their food rather than grow it. Depending on one export crop also leaves a farmer or a country exposed when its world price falls.
(c) Mismanagement of irrigation	Three named consequences. Soil erosion: water applied too heavily washes soil off the surface. Salinisation: irrigation water contains dissolved salts; in a hot climate the water evaporates and leaves the salts behind, and repeated over years the salt concentration in the topsoil rises until crops cannot take up water and the land goes out of production. Water logging: applying more water than drains away fills the pore spaces, excluding air, so roots cannot respire.
(d) Overuse of pesticides	Pesticide resistance: a few individuals in the pest population happen to survive; they breed, and the resistant form spreads until the pesticide no longer works, so stronger or more frequent doses are needed. Pest resurgence: a broad pesticide also kills the pest's natural predators, so when the pest recovers there is nothing to hold it back and its numbers rebound higher than before. Impacts on pollinators: bees and other pollinating insects are killed or weakened, and since many crops depend on them, yields of those crops fall.
(e) Overuse of fertilisers	The chain runs: leaching — fertiliser applied in excess of what the crop can absorb dissolves in rainwater and drains into rivers and lakes; nutrient enrichment — the added nitrate and phosphate feed the algae and plants already there; eutrophication — algae multiply into a bloom that covers the surface, blocking light so the plants beneath die, and when the algae and plants die the decomposers multiply and use up the dissolved oxygen in the water, so fish and other aquatic animals suffocate. Learn that as an ordered chain: it is marked as one.
(f) Exhaustion of nutrients in soils	Growing crops and removing the harvest takes ions out of the soil year after year. If the same crop is grown repeatedly, the same ions are removed in the same proportion; if crop residues are burned or taken away rather than returned, the organic content falls too, so the soil loses both its nutrient store and the structure that organic matter gives it. Yields fall, and more fertiliser is needed each year to get the same result.
(g) Removal of natural vegetation	Deforestation clears the trees whose roots bound the soil and whose canopy intercepted the rain, so soil is exposed and washed away. Overcultivation works the land too often and too hard, without rest or added organic matter, breaking down soil structure. Overgrazing keeps too many animals on an area so grass is eaten faster than it regrows and the ground is left bare and trampled. All three end in the same place: exposed soil with nothing holding it.
(h) Monoculture and intensification	A single crop across a large area supports far fewer species than a varied landscape, so there is a loss of biodiversity; hedgerows and field margins are removed to make bigger fields, taking away the remaining habitat. Because one crop attracts one set of pests, more pesticide is needed, and because one crop draws the same ions, more fertiliser is needed — and both lead to soil and water pollution. Intensification also concentrates livestock, so slurry and nutrients are produced in quantities the local land cannot absorb.
(i) Soil erosion	The end point of most of the above, and the syllabus names it as loss of topsoil and nutrients: the topsoil — the thin upper layer that holds the organic matter and most of the nutrients — is washed or blown away. What is left is less fertile, holds less water and grows less, so yields fall permanently. Topsoil forms at a rate of millimetres per century, so on any human timescale this is a loss that cannot be made good. Sub-topic 2.3 takes this apart properly.

The eutrophication chain in five words

Leaching → enrichment → algal bloom → light blocked → decomposers use the oxygen. The final mark is nearly always the oxygen: fish die because decomposers respiring aerobically have removed the dissolved oxygen, not because the algae poisoned them. Write “dissolved oxygen” and you have it.

Worked example A farmer has grown maize in the same field every year for twelve years, using increasing amounts of inorganic fertiliser and insecticide. Yields are now falling. Explain why, and suggest two changes that would make the farm more sustainable. [8]

Why yields are falling — reason 1, the soil

Growing the same crop every year removes the same mineral ions in the same proportions, so those ions are exhausted. Because inorganic fertiliser adds ions but no organic matter, the soil's organic content has fallen as well, so its structure, its ability to hold water and its population of soil organisms have all declined. The soil is therefore less able to supply the crop even when fertiliser is applied.

Why yields are falling — reason 2, the pests

A monoculture of one crop lets the pests of that crop build up in the soil and in the area year on year. Repeated insecticide use has selected for resistance: the individuals that survived have bred, so the population is now largely resistant and the insecticide is less effective. It has also killed the pests' natural predators, so pest resurgence occurs and numbers rebound higher after each application.

Why yields are falling — reason 3, if you need a third

Excess fertiliser that the crop cannot absorb is leached out by rain, so it is wasted and may cause eutrophication in nearby water. Bare soil between the rows of a single crop is also exposed to wind and rain, so topsoil and its nutrients are eroded.

Change 1 — crop rotation

Grow different crops in successive years, including a legume. Different crops remove different ions in different proportions, so no single nutrient is stripped out; the legume restores nitrogen to the soil; and the pests and diseases specific to maize cannot complete their cycle because their host is absent for a year or more, so less insecticide is needed.

Change 2 — organic fertiliser, or biological control

Apply manure, mulch or crop residue as well as, or instead of, some of the inorganic fertiliser. It releases nutrients slowly so less is leached, and it adds organic matter, which rebuilds soil structure and water retention. Alternatively, introduce a natural predator of the pest: it is specific, leaves no residues, does not select for resistance in the same way, and is self-sustaining once established.

Nutrient exhaustion plus lost organic matter, plus resistance and resurgence in the pest. Fix with rotation and with organic inputs or biological control.

Applied question A country's government is deciding whether to encourage farmers to switch from staple food crops to palm oil for export. Discuss the benefits and limitations of this policy. [6] ▼

This is exactly the kind of question where an unbalanced answer loses half the marks. Cash crops are on the syllabus as an impact of unsustainable agriculture, which tempts candidates to write only the harms — but the mark scheme has a benefits column, and the reason farmers switch is that the benefits are real.

Benefits

Palm oil earns considerably more per hectare than a staple crop, so farmers' incomes rise and rural poverty falls. Exports earn foreign currency for the national economy, which can pay for imported goods, infrastructure, health care and education. Processing, transport and port work create employment beyond the farm itself. Palm oil is also a high-yielding oil crop per hectare, so producing the same quantity of oil from an alternative would require more land.

Limitations

Land that grew food now grows an export crop, so the local food supply falls and prices rise; the people worst affected are those who buy food rather than grow it. Expanding plantations often means removing natural vegetation, so habitats and biodiversity are lost and soil is exposed to erosion. A large monoculture needs more fertiliser and pesticide, with the leaching and eutrophication risks that follow. And a farmer or country dependent on one export crop is exposed if its world price falls.

The judgement

Name who gains and who bears the cost, and over what timescale. The income is immediate and goes to the growers and exporters; the food-price rise falls on urban and landless households; the habitat and soil losses are long-term and fall on everyone. A defensible conclusion is that the policy can be justified if it is limited to land already cleared, if some land is reserved for food crops, and if the export income is used to keep food affordable — and is hard to justify if it means clearing forest and relying on a single commodity.

Source-led question · AO3

Figure 1 — how much fertiliser is the right amount?

2.2.3(i) puts inorganic NPK fertiliser on the list of strategies that raise yield, and 2.2.4(e) puts overuse of fertiliser on the list of things that damage the environment. Both are true, and this figure is where they meet. A farmer measured the grain yield of one field over several seasons at different nitrogen rates. Read it before you read the questions.

Figure 1. Grain yield against nitrogen fertiliser applied, one field, one crop. Constructed for practice, but the shape is the shape every real fertiliser trial produces: a steep rise, a flattening, a peak, then a fall.

Identifythe yield when no nitrogen fertiliser is applied.[1]

Describethe trend shown in Figure 1, quoting figures from both axes.[4]

Calculatethe extra yield gained from the fourth 40 kg of nitrogen (120 to 160) and from the fifth (160 to 200). Show your working.[2]

Explainwhy the yield falls above the optimum rate, and what happens to the nitrogen the crop does not take up.[5]

Evaluatewhether a farmer should apply the rate that gives the highest yield in Figure 1.[4]

Attempt all five before you open the mark scheme. The evaluate part is the one to spend time on — it needs a judgement, not a summary.

Source question 1 — identify

From Figure 1, which application rate gives the highest yield?

A 120 kg per hectare per year

B 160 kg per hectare per year

C 200 kg per hectare per year

D 240 kg per hectare per year

The curve reaches its highest point at 200 kg per hectare, where the yield is 8.7 t per hectare, and falls on both sides of it. Read the dashed lines down and across to the axes rather than judging by eye. At 160 kg the yield is already 8.5, only 0.2 below the peak, which is the point of the question: the last 40 kg buys very little.

Source question 2 — calculate

Yield rises from 3.0 t per hectare with no fertiliser to 8.7 t per hectare at the optimum rate. Calculate the percentage increase.

A 66 per cent

B 97 per cent

C 155 per cent

D 190 per cent

Change ÷ original × 100 = (8.7 − 3.0) ÷ 3.0 × 100 = 5.7 ÷ 3.0 × 100 = 190 per cent. The common error is dividing by the final value instead of the starting one, which gives 66 per cent; “increase” always means increase on what you started with. That figure is why inorganic fertiliser transformed food production: it very nearly trebles the yield of this field.

Model answer The five parts above, worked in full. [16]

Identify — read it off the axis

3.0 tonnes per hectare. That is the yield the soil gives on its own, from the nutrients already in it.

Describe the trend — three phases, and figures for each

Yield rises steeply at first, from 3.0 t per hectare with no fertiliser to 6.8 t at 80 kg per hectare. The rise then slows, reaching a maximum of 8.7 t at 200 kg. Above that rate the yield falls, down to 6.5 t at 320 kg. So the relationship is not proportional: each extra 40 kg adds less than the one before, and beyond the peak it does harm. The four marks are the rise, the flattening, the peak with its two coordinates, and the fall.

Calculate — the arithmetic that proves diminishing returns

120 to 160 kg: 8.5 − 7.9 = 0.6 t per hectare.
160 to 200 kg: 8.7 − 8.5 = 0.2 t per hectare.
The same 40 kg of nitrogen, and the same cost, buys three times as much grain the first time as the second. Earlier still, 40 to 80 kg gained 1.6 t. This is what diminishing returns means, and quoting two of these steps is worth more than the phrase on its own.

Explain the fall — the mechanism, then where the nitrogen goes

The crop can only take up so much nitrogen, so once its demand is met, something else limits growth — light, water, or another nutrient such as phosphate or potassium — and more nitrogen cannot raise the yield further. That accounts for the flattening. The fall above 200 kg has causes of its own: a high concentration of dissolved ions in the soil water makes it harder for roots to take up water, so the crop can wilt in dry weather; and a heavily nitrogen-fed cereal puts its growth into soft leafy tissue and a tall weak stem, which is more easily flattened by wind and rain and more readily attacked by pests and disease.
The nitrogen the crop does not take up stays as nitrate ions dissolved in the soil water, and nitrate is very soluble, so rain washes it down through the soil and into groundwater, streams and lakes — this is leaching. In the water it acts as a fertiliser for algae, which is nutrient enrichment, and the sequence that follows is eutrophication: algae multiply and form a surface bloom, the bloom blocks light so the plants beneath it die, bacteria decompose the dead material and use up the dissolved oxygen in doing so, and fish and other aquatic animals suffocate. So the fertiliser above the optimum is paid for twice, once at the farm gate and once in the river.

Evaluate — weigh it, then commit

For applying 200 kg: it is the highest yield the field can give, 8.7 t against 3.0 t unfertilised, and more food from the same hectare means less land needs to be cleared elsewhere.
Against: the last 40 kg gains only 0.2 t, so the fertiliser may cost more than the extra grain is worth; the surplus nitrate is the fraction most likely to leach; and the margin for error is small, since the curve turns over immediately after the peak and a slightly heavy application loses yield.
Judgement: no — a rate near 160 kg is the better choice, because it gives 8.5 t, within 0.2 t of the maximum, for 20 per cent less fertiliser and less leaching. What the judgement depends on is the price of fertiliser against the price of grain, and how close the field is to a watercourse. Splitting the dose across the season, testing the soil first, and using organic fertiliser for part of it would all reduce the loss further.

Rise, flatten, peak at 200 kg → 8.7 t, then fall. Above the optimum: another factor limits growth, and the surplus nitrate leaches → nutrient enrichment → eutrophication.

Checkpoint 2.2

Answer, then read the explanation even when you were right.

Your Score 0 / 23

Question 1

A farm keeps sheep and also grows wheat on the same land holding. This is best described as

A arable farming, because a cereal crop is being grown for sale

B mixed farming, because both crops and livestock are produced

C pastoral farming, because livestock are kept on the same land

D monoculture, because the whole holding is worked as one unit

Mixed farming is the term for crops and livestock together, and it has the practical advantage that manure fertilises the crops while residues feed the animals. Arable alone means crops and pastoral alone means livestock, so each of those describes only half of what the farm does. Monoculture means one crop species over a large area, which is the opposite of what is described.

Question 2

What does intensive agriculture mean?

A farming a very large area of land with low inputs per hectare

B high inputs per unit area to get a high yield from little land

C producing food only for the farmer's own family to eat

D growing one crop species repeatedly on the same land

Intensive is about inputs relative to area: labour, fertiliser, machinery, water or feed concentrated on a small area to raise yield per hectare. A describes extensive farming, which is the opposite. C is subsistence farming and D is monoculture — both real terms from the same objective, and both classified on a different axis from intensity.

Question 3

Which definition of sustainable food production matches the syllabus wording?

A producing enough food now by methods that keep the land productive

B reducing the quantity of food that is grown so that soils can recover

C growing food close to the towns and cities in which it will be eaten

D producing food without using any manufactured chemical inputs at all

The definition has two halves: sufficient food for the present generation, and methods that let future generations grow food from the same land. D describes organic farming, which is one approach rather than the definition. B drops the “sufficient food” half entirely, which is the commonest error here. C describes urban farming, a strategy from 2.2.3.

Question 4

Why does crop rotation reduce the need for pesticides?

A pests of one crop cannot build up when their host is absent

B rotated crops release chemicals that are toxic to insect pests

C the soil is left bare for a year, which kills the pests in it

D rotation raises the soil pH to a level pests cannot tolerate

Most pests and pathogens are specific to one crop, so changing the crop breaks their life cycle and stops populations accumulating in the soil year after year. B invents a chemical defence that rotation does not provide. C describes leaving land bare, which is not what rotation means and would cause erosion. D invents a pH effect.

Question 5

Why does drip irrigation use less water than flooding a field?

A the water is recycled back to the tank after passing the roots

B plants absorb water faster when it arrives through narrow pipes

C water goes to each plant, so little evaporates or drains away

D it is only ever used at night, when evaporation is much lower

Delivering water to the base of each plant means almost none is lost from bare ground between plants or evaporated from a flooded surface, and the soil is not saturated, which also reduces salinisation. A invents a recycling loop. B invents a change in the plant. D names a real way of reducing evaporation, but it is not what makes drip irrigation efficient.

Question 6

Which is a genuine limitation of using genetically modified crops?

A seed costs more and pests can evolve resistance to the trait

B modified crops always give lower yields than unmodified ones

C genetic modification cannot produce drought-tolerant varieties

D modified plants are unable to reproduce or to be grown at all

Cost of seed, dependence on a supplier, evolved resistance in pests and concerns about non-target organisms and gene transfer are the honest limitations. B contradicts the purpose of the technology, since higher yield is usually the point. C is false, as drought tolerance is one of the traits named. D is simply not true of modified crops as a class.

Question 7

Which is the main advantage of organic fertiliser over inorganic NPK fertiliser?

A it supplies a higher concentration of nutrients per kilogram

B its nutrients reach the roots faster after it has been applied

C it supplies the exact ratio of ions that the crop is short of

D it adds organic matter, improving soil structure and retention

Organic fertiliser feeds the soil as well as the crop: it improves structure, water retention and soil organisms, and releases nutrients slowly so less is leached. The other three are all genuine advantages of inorganic fertiliser, which is more concentrated, faster acting and precisely formulated — which is exactly why farmers use it.

Question 8

What is pest resurgence?

A a pest population becoming immune to a particular pesticide

B a pest spreading into a new country on imported plant material

C a pest moving from a wild plant onto a nearby cultivated crop

D a pest rebounding strongly after its predators have been killed

Resurgence is caused by the pesticide killing the pest's natural predators as well as the pest, so nothing holds the population back when it recovers. A defines resistance, which is the neighbouring term and the one most often confused with it. B and C describe ways a pest arrives, not why its numbers rebound.

Question 9

In eutrophication, what is the immediate cause of fish dying?

A nitrate ions in the water are directly poisonous to the fish

B the algal bloom blocks light so the fish cannot find their food

C decomposers respiring use up the dissolved oxygen in the water

D the water becomes too acidic for fish eggs to develop in it

The final step of the chain is oxygen: algae and plants die, decomposers multiply and respire aerobically, and the dissolved oxygen falls until fish suffocate. A assumes a direct toxicity that is not the mechanism here. B correctly notes that light is blocked, but that kills the plants below, not the fish. D imports acidification, which belongs to a different pollution topic.

Question 10

Why does irrigation in a hot dry region often lead to salinisation?

A fertilisers applied with the water react to form solid salts

B irrigation water dissolves the salt out of the rock beneath

C water evaporates and leaves its dissolved salts in the topsoil

D crops release salts from their roots into the surrounding soil

Irrigation water carries dissolved salts; the water evaporates in the heat and the salts stay behind, building up in the topsoil year after year until crops can no longer take up water. B reverses the direction, since salt is arriving from the water, not the bedrock. A and D invent processes that do not occur.

Question 11

Which statement about monoculture would an examiner credit in a balanced answer?

A it has no advantages, which is why it is on the syllabus list

B it lowers costs per tonne but reduces biodiversity on the farm

C it raises biodiversity because one crop supports many species

D it needs less fertiliser because only one crop is being grown

This kind of farm can be sown, treated and harvested with one set of machinery at one time, so costs per tonne fall and food is cheaper — and it supports fewer species and needs more of the same fertiliser and pesticide. A is the one-sided answer that caps marks. C reverses the biodiversity effect. D reverses the fertiliser effect, since one crop removes the same ions repeatedly.

Question 12

Which is the strongest argument for biological rather than chemical pest control on a long-established plantation?

A it eliminates the pest species completely within a single season

B the control organism can never become a problem in a new area

C it acts more quickly than a pesticide during a sudden outbreak

D it is specific, leaves no residues and sustains itself

Specificity, absence of residues and self-sustaining action are the real strengths, and they suit a long-term programme rather than an emergency. A overstates it: biological control reduces a pest rather than eliminating it. C reverses the comparison, since chemicals are the fast option. B denies the main risk of the method, which is exactly why introductions are researched first.

Question 13

A farmer plants alternating rows of maize and beans in the same field in the same season. This is best described as

A crop rotation, because a different crop follows each year

B intercropping, because two crops share the field in rows

C mixed cropping, because the crops are not planted in rows

D monoculture, because one field is worked as a single unit

These three are the most easily confused terms in the topic, so fix them apart now. Intercropping is two or more crops grown together in the same field at the same time in a definite arrangement — alternating rows or strips, as here. Mixed cropping is also two crops together at the same time, but scattered through the field with no set pattern. Crop rotation is different: only one crop at a time, and it is the sequence from one season to the next that changes. Monoculture is one crop over a large area, the opposite of all three. Maize and beans are the classic pairing because the beans are a legume and restore nitrogen the maize has used.

Question 14

Hydroponics is one of the controlled environments named in 2.2.3(e). How does it raise yield?

A the roots sit in nutrient solution, so supply is exact

B the plants are grown in a deeper, richer layer of topsoil

C the crop carries an inserted gene for resistance to drought

D manure is dug into the soil before each planting season

Hydroponics grows plants with their roots in a nutrient solution rather than in soil, so the grower sets exactly which ions the crop receives and how much water it gets, and no nutrient is lost to leaching or locked up by the soil. In a greenhouse, temperature, humidity and carbon dioxide can be controlled as well, and aeroponics goes further by misting the roots in air. B misses the point, since hydroponics uses no soil at all. C describes a genetically modified organism, which is 2.2.3(d). D is organic fertiliser, 2.2.3(j).

Question 15

Managed grazing means moving livestock between fields on a planned cycle rather than leaving them in one. Why does this produce more food from the same area of pasture?

A the animals are kept indoors, so they lose much less heat

B more animals are kept in each field for the whole year

C each field is ploughed yearly and resown with new grass

D grass in the rested fields regrows before it is grazed

This is 2.2.3(f), livestock rotation. While the herd is in one field the others are resting, so their grass regrows to full height before the animals return, and the pasture is never eaten faster than it grows back. That keeps a continuous cover of vegetation on the soil, which is also the direct opposite of overgrazing — the cause of bare soil in 2.3.1. B is overgrazing, which produces less rather than more. A and C describe different systems altogether and neither is what rotation means.

Question 16

A city government encourages vegetables to be grown on rooftops and on unused plots inside the city. Which is a genuine advantage of this urban farming?

A much larger areas can be cultivated than in the countryside

B rainfall is higher over a city, so less irrigation is needed

C food is grown near those who eat it, so transport falls

D city soil is naturally deeper and richer than farmland soil

Urban farming, 2.2.3(g), grows food inside the city on rooftops, balconies, walls and vacant land. Its real advantages are the short distance to the consumer, so less fuel is used in transport and less food spoils on the way; the use of land that was producing nothing; and a supply of fresh food to people who may live a long way from a farm. A is false — the area available is small, which is the main limitation. B and D are simply not true of cities, and urban soil is often contaminated, which is a second limitation worth knowing.

Question 17

What does agroforestry mean?

A growing trees on the same land as crops or livestock

B clearing forest so that a larger area can be cultivated

C growing a single species of tree over a large plantation

D planting trees only along the borders between countries

Agroforestry, 2.2.3(h), deliberately combines trees with crops or animals on the same land instead of separating them. The trees give shade and shelter, their roots hold the soil and reach water deeper than the crop can, their fallen leaves return organic matter, and they yield fruit, fodder or timber as a second income. It is also a wind break, so it appears again in 2.3.3(d). B is deforestation, C is a tree monoculture, and D describes nothing on this syllabus.

Question 18

About a third of the food produced in the world is never eaten. Why is that treated as an environmental problem and not only an economic one?

A wasted food is burned, which releases sulfur dioxide gas

B it lowers the price that farmers receive for their crop

C shops then import more of their food from other countries

D the land, water and fertiliser used to grow it are lost

This is 2.2.4(a). Every tonne of food that is thrown away also throws away everything that went into growing it: the land that was cleared and cultivated, the water used to irrigate it, the fertiliser and pesticide applied to it and the fuel burned by the machinery. So more land is farmed, and more intensively, than the population actually needs — which is why reducing waste is counted as a strategy for feeding people as well as a saving. B is a real economic effect but not an environmental one. A and C are not generally true.

Question 19

Farmers in a region replace their maize with cotton grown for export. What is the most likely impact on local people?

A soil erosion stops, because cotton binds the soil better

B less food is grown locally, so food prices tend to rise

C the growing season lengthens, so two harvests are possible

D fertiliser use falls, so less nitrate reaches the river

Cotton is one of the four cash crops named in 2.2.4(b), with coffee, soya beans and palm oil. The land is still farmed, but what it produces is sold abroad rather than eaten locally, so the local food supply falls and its price rises — and the households hit hardest are those who buy food rather than grow it. Note the balance the examiner wants: the farmers switch because cotton earns more, and that income is real. A, C and D each claim an improvement that does not follow from changing which crop is grown; a cash crop is usually grown more intensively, not less.

Question 20

An orchard is sprayed heavily with insecticide through the flowering season. Why can this reduce the yield of fruit?

A the chemical is taken up by the roots and blocks the stomata

B the trees absorb it, and it makes their leaves grow larger

C it washes into rivers, where it makes the algae grow fast

D pollinating insects are killed, so fewer flowers set fruit

Insecticides are not selective about which insects they kill, so bees and other pollinators die alongside the pests. Without pollination the flowers are not fertilised and no fruit forms, so spraying to protect the crop can be the thing that costs it — this is 2.2.4(d), and it sits beside pesticide resistance and pest resurgence in the same objective. C describes eutrophication, which follows fertiliser rather than insecticide. A and B invent mechanisms that do not happen.

Question 21

Growing the same crop on the same land year after year, with nothing added back, exhausts the soil because

A the pH rises steadily until the soil is strongly alkaline

B soil particles are broken down into much smaller particles

C the crop returns more organic matter than the soil can hold

D the same mineral ions are removed each year, not replaced

2.2.4(f) names two things that are exhausted: the inorganic ions and the organic content. One crop species takes up the same ions in the same proportions every year, so those particular nutrients run down while others are left; and harvesting the whole plant removes the residues that would have decomposed into organic matter, so soil structure and water retention decline as well. The two fixes are on the syllabus already — crop rotation in 2.2.3(a) and organic fertiliser in 2.2.3(j). C states the opposite of what happens, and A and B are not effects of cropping.

2.3 Soil Erosion ▼

▶ Watch: Soil Erosion, Terracing, Wind Breaks and Desertification

Links only, opening on YouTube in a new tab. This is the thinnest of the three lists and you should know that before you use it. Five videos, none of them made for 0680: three are general science, one is from a US soil-conservation agency and one is AQA GCSE Geography, which is a different syllabus with a different scope. Between them they cover erosion, terracing, contour ploughing, wind breaks and desertification. They do not cover bunds, addition of organic matter, mass movement, silting of rivers or displacement of people — four of those are named impacts or strategies you can be asked about directly, so take them from the tables above, not from here.

Why this sub-topic is the one to get right

Soil erosion is where 2.1 and 2.2 arrive. It has the cleanest cause-impact-strategy chain on the whole syllabus, and Cambridge examines it as a chain: a question will give you a photograph or a description of a hillside, ask you to identify the causes, then the consequences, then what could be done. If you can hold the chain, you can answer almost any version of it.

Start from one fact that makes everything else make sense. Topsoil is the thin upper layer that holds the organic matter and most of the nutrients, and it forms at a rate of a few millimetres per century. A single storm can remove what took hundreds of years to build. That is why soil erosion is treated as a permanent loss rather than a temporary problem, and saying so is very often the evaluation mark.

The single sentence that unlocks the whole sub-topic

Soil is lost when it is left bare, and it is held when it is covered. Every cause in 2.3.1 is a way of exposing soil; every strategy in 2.3.3 either puts a cover back on it, slows the water moving over it, or slows the wind moving across it. If you forget a specific item in the exam, work back from that sentence and you will construct a creditable answer.

2.3.1 The causes of soil erosion

Cause	How it exposes or removes the soil
(a) Unsustainable agricultural practices	Ploughing up and down a slope creates channels that run water straight downhill. Overcultivation without rest or added organic matter breaks down soil structure so the particles no longer hold together. Removing crop residues instead of returning them leaves the surface bare between harvests. Heavy machinery compacts the soil so rain cannot soak in and runs off the surface instead.
(b) Deforestation	Tree roots bind the soil together and the canopy intercepts the rain, so drops reach the ground gently and some water evaporates before it lands. Remove the trees and rain strikes bare soil at full force, dislodging particles, while there are no roots left to hold what remains. Deforested slopes are where erosion is fastest and most visible.
(c) Farming on steep slopes	Water runs faster downhill on a steep slope, and faster water carries more and larger particles. Gravity also moves loosened soil directly. The steeper the slope, the more soil a given rainfall removes.
(d) Bare soil	Soil with no vegetation cover has nothing to intercept the rain, nothing to bind it and nothing to slow the wind across it. Land is left bare between crops, after overgrazing, after burning, or during preparation for planting — and it is precisely in those gaps that most erosion happens.
(e) Wind and water erosion	These are the two agents that actually do the removing. Water: raindrops dislodge particles on impact, and surface run-off carries them away, first as a thin sheet and then in channels that grow deeper as more water is funnelled into them. (Geography names those channels rills while they are small and gullies once they are deep. That classification is background here — 0680 asks only for wind and water as the two agents.) Wind: dry, loose, fine particles with no vegetation to slow the air are lifted and blown away, which is why erosion by wind is worst on dry, bare, flat land.

2.3.2 The impacts of soil erosion

Impact	The mechanism
(a) Silting of rivers	Eroded soil is carried into rivers, where it settles as sediment. The river bed rises, so the channel holds less water and floods more readily; reservoirs behind dams fill with silt and lose capacity; irrigation channels and harbours must be dredged; and suspended sediment blocks light and smothers the habitats of river organisms.
(b) Desertification	Where topsoil is lost and vegetation cannot re-establish, land in dry regions gradually becomes desert-like: less soil holds less water, so fewer plants grow, so less soil is held and more is lost. It is a self-reinforcing loop, which is why it is so difficult to reverse once it starts.
(c) Mass movement: landslides, rockslides and mudslides	Without roots binding it and with water saturating it, a slope loses stability and a large volume of material moves downhill at once. This can destroy homes, roads and farmland and cause loss of life, and it happens most where slopes have been deforested or cut into. The three names are just the material that moves and the way it moves: a landslide is soil and loose material sliding down a slope as a mass; a rockslide is the same movement in rock that has broken away from a cliff or a cut face; a mudslide is soil so saturated by heavy rain that it flows rather than slides. One clause each is enough — the objective asks for mass movement as an impact, not for the geology of it.
(d) Loss of habitats and biodiversity	Soil is a habitat in itself, for bacteria, fungi, insects and earthworms; losing it removes them and the plants that depend on them. Silt washed downstream also damages river and coastal habitats, so the loss is not confined to the field it came from.
(e) Reduction in crop yield	The topsoil carried away is the layer holding the organic matter and most of the nutrients, and the remaining subsoil holds less water and has poorer structure. Yields fall, and the farmer must spend more on fertiliser and irrigation to get less.
(f) Malnutrition and famine	Where people depend on the food they grow, falling yields mean less food and less income to buy any. Persistent shortage causes malnutrition, and a harvest failure on already degraded land can cause famine. This is the point at which an environmental problem becomes a human one.
(g) Displacement of people	When land can no longer support the people farming it, they move — usually to cities, sometimes across borders. That puts pressure on housing, water and services where they arrive, and the land they leave often degrades further with nobody managing it.

Chain the impacts, do not list them

An answer that reads “topsoil is lost, so yields fall, so farmers have less food and less income, so malnutrition rises and people move away” scores far better than four separate bullet points, because each “so” is the link the mark scheme is looking for. The same trick works upstream: “soil is washed into the river, so the bed rises, so the channel holds less water, so flooding is more frequent.”

2.3.3 Strategies to reduce soil erosion

The syllabus gives each strategy together with the reason it works — that is unusually generous, and it means the mechanism is examinable. Learn each strategy with its mechanism attached.

Blue arrows show surface run-off; grey arrows show wind. On the untreated slope nothing interrupts the flow.

Strategy	How it works (the syllabus gives these reasons, so use its words)
(a) Terracing	Reduces movement of soil and surface run-off. A long slope is cut into a series of level steps, each with a lip. Water reaching a step stops and soaks in rather than running on, so it never builds up the speed needed to carry soil, and any soil that does move is caught on the step below. Terracing makes steep land farmable at all, but it is very labour-intensive to build and must be maintained, or a collapsed terrace concentrates the water instead.
(b) Contour ploughing	Reduces surface run-off. The field is ploughed along the contours — across the slope rather than up and down it — so each furrow lies horizontally and acts as a small barrier holding water back and letting it infiltrate. Ploughing up and down does the opposite: every furrow becomes a channel guiding water straight downhill. It costs nothing extra beyond driving in a different direction, which makes it one of the highest-value strategies on the list.
(c) Bunds	Reduces surface run-off, reduces wind speed and wind erosion. Bunds are low banks or walls of earth or stone built across a slope or around a field. They trap water behind them so it soaks in rather than running off, and they trap soil that is already moving. Standing above the surface, they also break the wind at ground level. They are cheap, can be built from local material, and are widely used in dry regions.
(d) Wind breaks	Protects crops, reduces wind speed and wind erosion. Rows of trees or hedges planted across the prevailing wind slow the air before it reaches the field, so it can no longer lift dry soil particles, and the crop itself is not damaged or dried out by strong wind. The trees also provide shade, habitat and sometimes fruit or timber. They occupy some land and compete with the crop at the field edge.
(e) Maintaining vegetation cover	Roots bind the soil, and the vegetation reduces surface run-off and absorbs water. Keeping something growing — a cover crop between harvests, grass strips, or simply not clearing the land — means the leaves intercept the rain so it does not strike bare soil, the roots hold the particles together, and the plants take up water so less runs off. It is the single most effective thing a farmer can do, and it is the direct answer to cause (d), bare soil.
(f) Addition of organic matter	Improves soil structure. Manure, compost, mulch and returned crop residues bind fine particles into larger crumbs that are heavier and harder to wash or blow away, and that leave larger pore spaces so water soaks in instead of running off. Organic matter also holds water like a sponge and feeds the soil organisms whose activity maintains the structure. It works slowly and needs to be repeated.

Which strategy for which problem

Water on a slope → terracing, contour ploughing, bunds. Wind on flat dry land → wind breaks, bunds. Bare soil anywhere → maintain vegetation cover, add organic matter. Bunds appear in two of the three because the syllabus credits them for both water and wind — which makes them a safe answer when you are not sure which agent a question is describing.

Worked example A hillside was cleared of forest and planted with maize, ploughed up and down the slope. After three years, deep channels have formed, the river below runs brown after rain, and yields have halved. Explain the causes of the erosion and suggest three strategies to reduce it. [8]

Causes — take them from the description, one at a time

Deforestation: the tree roots that bound the soil have gone and the canopy that intercepted the rain has gone, so raindrops now hit bare soil at full force and dislodge particles. Farming on a steep slope: water runs faster downhill, and faster water carries more soil. Ploughing up and down the slope: every furrow acts as a channel directing run-off straight downhill, which is why the channels (rills and gullies) have formed. Bare soil: a maize field is exposed for part of the year between harvest and the next crop, with nothing intercepting the rain.

Link the observations to the impacts

The brown river is the eroded topsoil being carried away and will lead to silting, raising the river bed and increasing flood risk downstream. The halved yield is because the topsoil that held the organic matter and most of the nutrients has gone, leaving subsoil that holds less water and fewer ions.

Three strategies, each with its mechanism

Contour ploughing: plough across the slope so each furrow lies along the contour and acts as a barrier, reducing surface run-off. It costs nothing but a change of direction, so it is the first thing to do. Terracing: cut the slope into level steps so water stops and soaks in and soil cannot travel far — effective on steep ground, though labour-intensive to build. Maintaining vegetation cover: plant a cover crop between maize crops, or grass strips along the contours, so roots bind the soil, leaves intercept the rain and the plants absorb water, reducing run-off.

A sentence that lifts the answer

Add the timescale: the topsoil already lost took centuries to form and will not be replaced within the farmer's lifetime, so these strategies protect what is left rather than restoring what has gone. Adding organic matter would help rebuild structure in the remaining soil.

Causes: deforestation, steep slope, ploughing up and down, bare soil. Strategies: contour ploughing, terracing, vegetation cover — each with the reason the syllabus gives.

Source-led question · AO3

Figure 2 and Table 2 — the same rain on four different fields

A farm on a hillside above a river is divided into four fields. Soil loss was measured on each of them over one year. The map shows where the fields are, how steep each one is and how the ground is covered; the table gives the measurements. Two of the fields are on identical slopes, which is the comparison the data is built around.

Figure 2. Schematic map of the farm; a plan view, so the slope is given as a figure rather than drawn. Constructed for practice.

Field	Slope gradient	Ground cover	Soil loss / tonnes per hectare per year
Field P	3°	crop, soil bare between the rows	4
Field Q	8°	crop, soil bare between the rows	18
Field R	15°	crop, soil bare between the rows	42
Field S	15°	terraced, with a cover crop	9

Table 2. Measured soil loss for each field over one year.

Statethe soil loss from field Q.[1]

Describethe relationship between slope gradient and soil loss for the three bare fields P, Q and R, using figures.[3]

Calculatehow many times greater the soil loss from field R is than from field P.[2]

Explainwhy field S loses so much less soil than field R, although the two are on the same gradient.[4]

Suggesttwo strategies the farmer could use on field Q, and explain what each would achieve. Then state one impact the farm is having on the river.[5]

Write all five out first. The describe part is the one where marks are usually lost, because the figures get left out of it.

Source question 1 — identify

Using Figure 2 and Table 2, which field is on the steepest slope with soil left bare between the rows?

A field P, on the gentlest ground, closest to the river

B field Q, on the middle part of the hillside, above P

C field R, on the upper part of the hillside, next to S

D field S, which is terraced and carries a cover crop

Field R: the map gives it a slope of 15°, the steepest on the farm, and the key shows it as bare between the rows. S is on the same 15° slope but the key shows it terraced with a cover crop, which is what makes the pair worth comparing. P at 3° and Q at 8° are bare too, but on gentler ground. This is an identify part with two conditions in it — check both against the source before you answer.

Source question 2 — calculate

Fields R and S lie on the same 15° slope. Calculate the percentage reduction in soil loss on S compared with R.

A 21 per cent

B 33 per cent

C 79 per cent

D 367 per cent

(42 − 9) ÷ 42 × 100 = 33 ÷ 42 × 100 = 78.6 per cent, so about 79 per cent. Divide by R, because R is the value being reduced from. 33 per cent is the loss expressed as tonnes rather than as a proportion, and 367 per cent is the answer you get from dividing by S instead — a percentage reduction can never be more than 100.

Model answer The five parts above, worked in full. [15]

State — with its unit

18 tonnes per hectare per year.

Describe the relationship — direction, rate, figures

For the three fields with bare soil, soil loss increases as the slope gets steeper, and it increases faster than the gradient does: from 4 t per hectare at 3° to 18 at 8° and 42 at 15°. The gradient increases five-fold from P to R while soil loss increases about ten-fold, so the relationship is not a straight line. Field S does not fit the pattern, and that is because its ground cover is different rather than its slope.

Calculate — a ratio, not a percentage

42 ÷ 4 = 10.5 times greater. Read the command word: this one asks “how many times”, so it wants a ratio and not a percentage change, and writing 950 per cent here would be answering a different question.

Explain the difference — both features of field S, each with its mechanism

Field S is terraced: the slope has been cut into level steps, so water reaching a step stops and soaks in instead of running on, and it never builds up the speed needed to carry soil. Any soil that does move is caught by the step below. Field S also carries a cover crop: the leaves intercept the rain so drops do not strike bare soil at full force and dislodge particles, the roots bind the soil together, and the plants take up water so less of it runs off the surface. Field R has neither, so on the same 15° gradient it loses 42 t per hectare against S's 9 — a reduction of about 79 per cent. The pair is the whole argument of 2.3.3 in two rows of a table: the gradient is fixed, so what changed the answer was the management.

Suggest — apply it to a field you have not been told about

Contour ploughing: plough across the slope rather than up and down it, so each furrow lies along the contour and acts as a small barrier that holds water back and lets it soak in, reducing surface run-off. It costs nothing but a change of direction, so on a 8° slope it is the first thing to try. Maintaining vegetation cover, by planting a cover crop between harvests or leaving grass strips along the contours, so roots bind the soil, leaves intercept the rain and the plants absorb water. Bunds would also be creditable: low earth banks across the slope trap both water and the soil already moving.
The impact on the river: the soil washed off these fields is carried into it and settles as sediment, which is silting. The river bed rises, so the channel holds less water and floods more readily; suspended sediment also blocks light and smothers the habitats of river organisms. Field P is the field next to the river, so what leaves it arrives fastest.

The sentence that lifts the answer

Put a timescale on it. Topsoil forms at a few millimetres per century, so the 42 tonnes per hectare leaving field R each year is not being replaced within the farmer's lifetime. Strategies protect what is left; they do not restore what has gone.

Steeper and bare → more loss, and faster than in proportion. Same gradient, different management → 79 per cent less loss. Downstream, the missing soil turns up as silt.

Checkpoint 2.3

Answer, then read the explanation even when you were right.

Your Score 0 / 14

Question 1

Why does removing trees from a hillside increase soil erosion?

A the soil becomes far too acidic once the leaf litter is removed

B roots no longer bind the soil and rain is no longer intercepted

C the slope of the hillside becomes steeper once trees are cleared

D tree stumps left in place channel the water into deeper gullies

Trees do two jobs at once — roots hold the particles together and the canopy takes the force out of the rain — and clearing them removes both. A imports a pH change that does not follow. C describes something that clearing does not do, since the gradient is unchanged. D invents a mechanism; stumps and their remaining roots actually hold soil for a time.

Question 2

Why is ploughing up and down a slope worse than ploughing along the contours?

A each furrow becomes a channel guiding run-off straight downhill

B it turns the soil to a greater depth and so buries the topsoil

C it takes longer, so the soil is left exposed for more of the year

D it compacts the soil more heavily under the weight of the tractor

The direction of the furrows decides where the water goes: along the contour they hold it back, up and down they conduct it away and it accelerates. C invents a difference in time. B invents a difference in depth. D names a real problem with machinery, but compaction does not depend on which way the tractor is driven.

Question 3

How does terracing reduce soil erosion?

A it raises the pH of the soil so that crops can grow more strongly

B it drains water off the hillside faster before it can carry soil

C level steps stop the water, so it soaks in instead of running on

D it shelters the crop from wind arriving across the open hillside

Terraces break a long slope into level steps, so run-off is halted, infiltrates, and never gains the speed needed to carry soil. B is the opposite of the mechanism: the aim is to slow water down, not to move it off faster. A invents a pH effect. D describes a wind break, which is a different strategy for a different agent.

Question 4

Which strategy is credited by the syllabus with reducing both surface run-off and wind erosion?

A contour ploughing, which follows the contours across the slope

B bunds, which are low banks built across a slope or field edge

C terracing, which cuts the hillside into a series of level steps

D adding organic matter, which binds particles into larger crumbs

The syllabus attaches three reasons to bunds: they reduce surface run-off, reduce wind speed and reduce wind erosion, because a raised bank blocks both moving water and moving air. Contour ploughing and terracing are both credited for run-off only. Adding organic matter improves structure, which helps against both agents indirectly, but that is not the reason the syllabus gives.

Question 5

Why does maintaining vegetation cover reduce soil erosion?

A roots bind the soil, and the plants absorb water and slow run-off

B the plants take up the eroded soil particles through their own roots

C vegetation raises the temperature of the soil so it dries faster

D the crop uses up all the rainfall so no water reaches the ground

Three mechanisms combine: roots physically hold the particles, leaves intercept the rain so drops do not strike bare soil, and the plants absorb water so less runs off. B describes something roots do not do. C would make wind erosion worse, not better. D overstates absorption into an impossibility.

Question 6

A river downstream of eroding farmland floods more often than it used to. What is the most likely reason?

A more rain now falls on the catchment than fell there previously

B silt has raised the river bed, so the channel holds less water

C the eroded soil has made the river water too acidic to absorb

D the soil upstream now absorbs and holds far more water than before

Silting raises the bed, reduces the capacity of the channel, and so the river overtops its banks at a lower flow than before. (Run-off from bare soil arriving faster is a second valid reason.) A changes the rainfall, which the question does not. C invents an acidity effect. D reverses what erosion does to infiltration.

Question 7

Why is the loss of topsoil treated as a permanent loss rather than a temporary one?

A topsoil that has been eroded cannot be transported by any river

B fertiliser can never restore any of the nutrients that were lost

C soil forms far more slowly than erosion is able to remove it

D the subsoil beneath is completely unable to support plant life

It is a mismatch of rates, exactly like the definition of a finite resource in Topic 1: soil forms far more slowly than it is removed. A is false, since transport by rivers is how it is carried away. B overstates it, because fertiliser does replace nutrients — what it cannot replace is the organic matter and structure. D is too absolute, since subsoil supports poorer growth rather than none.

Question 8

Which conditions make wind erosion most likely?

A a wet clay soil on a steep slope that is covered with growing crops

B a moist loam soil sheltered by hedgerows on all four sides

C a damp soil bound by tree roots after heavy overnight rain

D a dry and bare soil of fine loose particles on flat open land

Wind lifts particles that are dry, fine, loose and unprotected, and open flat land lets the wind reach full speed across the surface. The other three each contain at least one feature that prevents it: moisture makes particles stick together, roots bind them, and hedgerows and crops slow the wind before it reaches the soil.

Question 9

How does adding organic matter reduce soil erosion?

A it improves structure, binding particles into crumbs that resist

B it kills the soil organisms that loosen the particles by burrowing

C it adds weight so that the soil is too heavy for wind to lift it

D it makes the soil surface waterproof so that no rain enters it

Organic matter binds fine particles into larger, more stable crumbs, which are harder to detach and which leave larger pores so water infiltrates instead of running off. D would make run-off worse by preventing infiltration. B reverses the role of soil organisms, whose activity builds structure. C confuses structure with sheer mass, and organic matter is light.

Question 10

Which sequence correctly links a cause of soil erosion to its social impact?

A overgrazing raises soil fertility, so more people move onto the land

B silting of rivers improves irrigation, so farmers abandon their fields

C terracing exposes the topsoil, so malnutrition becomes more common

D overgrazing bares the soil, yields fall, and people are displaced

The chain runs cause to impact to consequence for people: grass is eaten faster than it regrows, the ground is left bare, topsoil is lost, yields fall, and eventually the land cannot support those farming it. A reverses the effect of overgrazing on fertility. C calls a protective strategy a cause. B pairs a real impact with a benefit and a conclusion that do not follow from it.

Question 11

Question 5 asked which strategy is credited with reducing both surface run-off and wind erosion. Which strategy is credited with protecting the crop and reducing wind speed, but not with reducing surface run-off?

A wind breaks, rows of trees planted across the wind

B bunds, low banks of earth built across the slope

C terracing, cutting a slope into a set of level steps

D contour ploughing, driving across the slope not down

Read the syllabus wording for the two side by side. Wind breaks, 2.3.3(d): protects crops, reduces wind speed and wind erosion — three things, and run-off is not one of them, because a row of trees does not lie across the path of water moving over the ground. Bunds, 2.3.3(c): reduces surface run-off, reduces wind speed and wind erosion — a bund is a physical bank across the slope, so it stops water as well as wind, which is what makes it the safe answer when a question does not say which agent is at work. Terracing and contour ploughing are water only.

Question 12

Why is desertification described as a self-reinforcing process?

A deserts spread outwards at a fixed rate once they have begun

B rainfall in a region drops as soon as its topsoil is eroded

C farmers move away, so the land is left to recover by itself

D less soil holds less water, so fewer plants grow and bind it

This is the loop in 2.3.2(b), and being able to state it as a loop is what separates a good answer from a list. Topsoil is lost, so the soil that remains holds less water; less water means fewer plants can grow; fewer plants means fewer roots binding the soil and less cover intercepting the rain, so still more soil is lost. Each turn of the cycle makes the next turn worse, which is why land is far easier to protect than to restore. A is a description with no mechanism in it. B reverses cause and effect. C is the opposite of what happens, since abandoned degraded land usually erodes further.