🎯 Context

You have spent three lessons underground. You know what a soil is made of, why its texture decides how much water and how many nutrients a plant can actually reach, and what it takes to keep soil on a slope rather than in a river.

Now come up to the surface. Something is growing on almost every soil worth farming, and in every case somebody decided what. That decision looks completely different on the plain below Geneva Airport, on the mountains of northern Sweden, and on a forested hillside in north-east India.

Those differences are not random, and they are not simply a matter of how rich the country is. They follow from the soil and the climate underneath, and from the market, the machinery, the law and the culture on top. This lesson is about all of it: how much land there actually is, why it carries such different kinds of farming, and who gets left out when decisions about land are made.

https://www.youtube.com/watch?v=SsCYEemoGlM

Phase 1: There is only so much of it

5.2.1 Land is a finite resource, and the human population continues to increase and require feeding.

About 70% of ice-free land is used for agriculture and forestry. Not all soils or land are suitable for arable crops; some land is too steep, some soils are too nutrient-poor. These are often used for livestock production.

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Finite, and most of it is not good enough

Start with the number that frames the whole of this sub-unit. About 70% of the world's ice-free land is already used for agriculture and forestry. The population that has to eat from it keeps rising. The land does not.

That is what finite means here, and the real limit is tighter than the total, because land is not interchangeable. Ground is only useful for crops if the climate gives a long enough growing season, the slope is gentle enough to work, and the soil holds enough water and enough nutrients to carry a crop, which is exactly what you spent last lesson on. Fail any one of those and you cannot plough it.

Land that fails is marginal land. Too steep, too high, too cold, too dry, too thin, too poor. Marginal land is not wasted land: grass grows on a great deal of it, and animals eat grass. So the usual answer to marginal land is livestock. Cattle, sheep and goats convert vegetation that humans cannot digest into milk and meat, on ground that would never carry a crop.

Switzerland is the clearest example you will ever stand in. In 2024 the country farmed 1,040,512 hectares. Only 38% of that was under arable crops. 58% was natural meadow and pasture, because most of Switzerland is too steep, too high or too cold for anything else. This country is not short of farmers. It is short of flat, low, fertile ground.

Task

State three physical reasons why an area of land might be unsuitable for arable crops.
Explain why the total area of farmland is a poor guide to how much food a country can grow.
Marginal land yields far less food per hectare than good arable land. Suggest why it is farmed at all.

Local example: the fields Switzerland is not allowed to build on

Switzerland decided some time ago that its best soil was too important to leave to chance. Since 1992 a federal plan has protected surfaces d'assolement, the crop rotation areas: the flat, deep, workable soils with the highest yield potential.

The plan sets a floor. At least 438,460 hectares must be safeguarded across the country, and every canton carries a share of it. The cantons currently safeguard 445,680 hectares, about 11% of the national territory and 31% of all farmland. The margin above the legal floor is 7,220 hectares, roughly 1.6%.

The figure is not arbitrary. It is calculated from a food supply of 2,340 calories per person per day in a serious shortage, which works out at about 506 m² of protected cropland per person.

Bring it closer. The canton of Geneva must guarantee 8,400 hectares at all times. Its current inventory, approved on 1 November 2023, holds 8,457 hectares. Fifty-seven hectares of slack, in a canton under permanent pressure to build.

Why a law rather than good intentions? Because of the rate you met last lesson. Swiss soils form at roughly one centimetre per century. Tarmac takes an afternoon. Built land does not come back, so the plan treats the best soil as a stock that can be spent but never replaced.

Sources: Federal Office for Spatial Development (ARE), statistics on crop rotation areas; Canton of Geneva, inventaire des surfaces d'assolement.

Task

Explain why building on crop rotation areas is treated as a permanent loss rather than a temporary one.
Geneva holds 57 hectares above its legal minimum. Suggest what that means for a canton deciding whether to approve a large new development.

Phase 2: Why farming looks different from place to place

5.2.4 Agriculture systems across the world vary considerably due to the different nature of the soils and climates.

Soils in different biomes have very different potentials for crop types and productivity.

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Two things set the limits, and the farmer chooses inside them

Two things decide what can be farmed anywhere on Earth: the soil and the climate. Everything else is a choice made within those limits.

The soil side is last lesson's work. Texture decides how much rain is held where roots can reach it and how much drains straight past, and how well nutrients are held rather than leached away. The amount of organic matter decides much of the rest.

The climate side comes down to temperature and water. Temperature sets the growing season, the number of days warm enough for a crop to develop and ripen. Water decides whether a crop can be rain-fed or has to be irrigated.

Put the two together and the global pattern follows.

Tundra: a very short growing season, cold soils, often waterlogged, so decomposition is slow and organic matter accumulates. Almost nothing arable will ripen.
Tropical rainforest: enormous plant growth, but warm moist conditions make decomposition just as fast, so very little organic matter builds up in the soil. Most of the nutrients are in the trees, not underneath them.
Temperate western Europe: moderate temperatures, several months of growing season, rain spread through the year, soils with a decent organic matter content. This combination gives the most reliable cropland in the world.

You do not need a continent to see it. The Geneva plain grows wheat, rapeseed and sunflower. Climb into the Jura or the Alps and it is grass all the way up, because the season shortens, the slopes steepen and the soils thin out.

So: the soil and the climate set what is possible. The farmer chooses within that. The next phase is about the choosing.

Task

Explain why a deep, fertile soil is still of limited use for crops if the growing season is short.
A rainforest is one of the most productive ecosystems on Earth, yet the soil under it holds little organic matter. Explain why, and suggest what that means for farming the land once the forest is cleared.

🎯 Context

Phase 1: There is only so much of it

Finite, and most of it is not good enough

State three physical reasons why an area of land might be unsuitable for arable crops.

Explain why the total area of farmland is a poor guide to how much food a country can grow.

Marginal land yields far less food per hectare than good arable land. Suggest why it is farmed at all.

Local example: the fields Switzerland is not allowed to build on

Explain why building on crop rotation areas is treated as a permanent loss rather than a temporary one.

Geneva holds 57 hectares above its legal minimum. Suggest what that means for a canton deciding whether to approve a large new development.

Phase 2: Why farming looks different from place to place

Two things set the limits, and the farmer chooses inside them

Explain why a deep, fertile soil is still of limited use for crops if the growing season is short.

A rainforest is one of the most productive ecosystems on Earth, yet the soil under it holds little organic matter. Explain why, and suggest what that means for farming the land once the forest is cleared.