Unit C5


Agriculture involves the planting of plants or the raising of animals on the land in order to produce something useful. It means making some effort to use the land or to manage it. It can be as simple as sticking a root in the ground in a forest clearing, or as elaborate as the giant machine ploughed, planted, sprayed and harvested fields of modern agro-industries.

Because we do something to the land in order to produce what we need, we take on the responsibility to manage the land and the plants and animals we put on it or leave on it. This is not the place for detailed instructions in agriculture or the economics of agriculture. Our aim is to show how the environment affects agriculture and how these influences can be used or managed to make agriculture more successful.

A renewable resource

Agriculture is often called a renewable resource because, if the land is used with care, it can continue to produce indefinitely. One of the most important roles of environmental management in agriculture is to make sure that it is truly renewable, and that the ability of the land to produce is not damaged by its use.

Agricultural development of the land often goes through stages, a first pioneering stage, then maturity, and all too often a decline. The pioneering stage is on land that is newly cleared from its natural state. The soil has generally been made fertile by the forest that was growing on it. Such virgin soil is easy to develop and will produce well without much effort. However, if care is not taken (and the need is often not seen until too late), the soil fertility will decline and much of the agricultural potential of the land will be lost, especially in the tropics where the process goes much faster. Such agriculture is like mining the land, it is used up and then abandoned. This occurs often when pioneering or colonizing peoples settle on the land. They lack local knowledge, and their early success only makes their ultimate failure more difficult.

The land and people that survive this pioneering stage may be able to develop a more mature form of agriculture adapted to the land and the environment, and much more sustainable. There are traditional agricultural areas that have been in use for hundreds of years. However, even in these areas there is the risk of a slow erosion of the top soil layer that will eventually mean a decline in productivity. The world has too many deserts and rocky hillsides that were once important agricultural areas, and the loss of agricultural land is worrying even the richest and most successful countries. Even where knowledge and experience have shown how to do sustainable agriculture, there may be economic pressures for short-term gain that prevent it.

Any damage to the ability of the land to produce is a threat to the future. At a time when populations are generally increasing and there are more and more mouths to feed, the destruction of the ability of the land to produce food can only lead eventually to famine and death.

Soils and agriculture

The soil often limits agricultural production. Only certain soils are rich enough and stable enough for regular cultivation. Other soils may be suitable for pasture or tree crops. Poor soils may have no agricultural potential, and any attempt to develop them would be a waste of time and effort. Some soils may lack certain minerals required by some crops, while others may have so much as to be poisonous to many plants.

Soils can sometimes be improved by adding fertilizers or other chemicals, or by putting in humus or other organic matter, but this is expensive and sometimes difficult to do on a large scale. It is easier to keep a soil good than to restore it once it has been damaged.

It is essential to pick crops that will grow well in your soil. Farmers used to do this by trial and error, but today an agricultural specialist or extension agent can help to choose the plants most suited to a particular soil. Even then some trials would be wise before making a major investment in planting a new crop.

Climate and weather

Each plant has temperatures at which it grows best, as well as high and low temperatures that will kill it, and these are different for each kind and variety of plant. Plants also have different needs for water which may change as they grow, and some can stand being dry or flooded better than others. It is thus the climate as expressed by the weather through the year that limits what can be grown on any particular soil.

In considering the effect of climate on crops, both average conditions and the occasional extreme are important. The closer conditions are to the ideal for a plant, the better it will grow. But only one day that is too hot or too cold may kill it. The extreme condition need not occur very often for it to be disastrous for agriculture. Cyclones, droughts, floods, and rare cold spells all can be important limits on agricultural development.

It is possible to change some aspects of the climate as they affect agriculture. Careful selection of the land can reduce the risk of wind damage or flooding. Rows of trees can be planted as wind-breaks to shelter crops. Proper drainage or the construction of rows or mounds can reduce the damage from flooding. Irrigation can provide water when natural rainfall is insufficient. The limitations then become economic rather than climatic.

Biological interactions

Almost all crop plants and domestic animals have been introduced from somewhere else, and are grown close together in large numbers. As with any large-scale introduction of an organism that does not naturally occur in a place, there is a risk of imbalances, and particularly of the rapid spread of pests or diseases.

When a crop is grown over large areas, any pest that takes a liking to it will find an abundant food supply, and will be able to multiply very rapidly. While it may be technically easier and more economic to plant large fields of the same thing, it will also be necessary to use more pesticides because the crop will be more vulnerable to attack.

The presence of certain pests and diseases in a country may limit its agricultural productivity, and the introduction of a new pest or disease from overseas can be a disaster for even a well-established agricultural programme.

There can also be the problem of aggressive weeds or shrubs that can smother gardens and crowd out more useful plants in pastures, and that may be very difficult and expensive to control.

Since island ecosystems are vulnerable to introductions and lack many natural controls that would keep pests from getting out of hand, island farmers must be particularly careful in choosing what they grow and how they grow it, and in avoiding accidental introductions. This is why countries have plant quarantine restrictions to keep dangerous pests and diseases from coming into their country.

Choice of varieties or races

Each individual plant or animal is a little bit different from others even of the same kind, and it is these differences that lead to the many varieties or races that a farmer can choose from. Each variety will do best under some conditions and less well under others. No one variety will be best everywhere.

The conditions for agriculture on an island are very different from place to place, even over short distances. These microclimates depend on the shape of the land, the altitude, the direction of the prevailing winds, whether it is the wet or dry side of the island, the distance from the sea, the surrounding vegetation, and other things. It is therefore necessary to choose the varieties that do best under your particular conditions.

This principle was well known in traditional agriculture, when many varieties were grown even by the same village. Some were adapted to different soils or fields, or even to different parts of the same garden. Some did best under good conditions, while others would survive and produce even in a bad year. Those that did not taste as good might better resist a cyclone or drought, or an attack by a pest or disease. New varieties were sometimes exchanged on inter-island voyages, or they might be discovered growing in the forest or in an abandoned field. A wise farmer compares the performance of all his plants, and selects the biggest and strongest or most resistant for use in the next planting. In this way the planting stock is constantly improved.

Today, agricultural specialists and plant breeders can cross different varieties to produce a particular set of characteristics such as resistance to disease, good response to fertilizer, good quality for marketing, etc. Such varieties are well adapted to commercial agricultural production. However, even the most highly-recommended varieties need to be tested for their suitability to local conditions. They also can be more vulnerable to unfavourable conditions, where a mixed planting of different varieties or crops would give a greater chance of at least some success.

Small scale trial planting can help to show the most appropriate varieties for local conditions. Since the weather can be very different from year to year, it may take several years of trials before a final choice is made. This takes time, but it is the essential foundation on which a stable and productive agriculture can be built.

Many agricultural projects have failed because the wrong varieties were selected, or because some pest or disease could not be controlled, or because the soil or climate were not well suited to the crop. Successful agriculture requires careful attention to all these ecological and environmental factors.


The raising of animals such as beef cattle, dairy cows, horses, sheep or goats in pastures adds an additional complication to agriculture through the animals that feed on the plants. It is necessary to manage both the productivity of the plants in the pasture and the effects of the animals on the plants.

Plant growth in a pasture varies with the season, and there may be little or no growth during the dry season. The amount of food produced determines the carrying capacity of the pasture. The number of animals should not be more than the growth of the plants is able to feed over a full year, without the plants being all eaten up. If there are too many animals, they will graze the plants down to the roots, killing them or slowing their growth. Some plants (usually those most preferred by the animals) may disappear from the pasture. Only plants that the animals do not like to eat will increase, and these may take over the pasture replacing the good plants. As the soil is exposed by overgrazing, it is easily eroded, reducing the productivity of the pasture even more. If the pasture is too badly damaged, it may never recover.

The plants are the first to show signs of overgrazing; the kinds of plants will change, there will be fewer of them, and they will cover less of the soil. Only unwanted plants will increase. Next comes the signs of erosion: bare ground, gullies, and tufts of grass on pedestals of higher soil surrounded by lower more eroded soil. The productivity of the pasture as shown by the number of animals that can live on it may only decline after the real damage has been done.

While it may seem easiest to let the animals roam freely over a large area looking for whatever food is available, this may lead to damage of the most preferred areas. Stream banks and areas around water are particularly vulnerable. It may be better to use smaller areas of pasture, perhaps improved by fertilizing and by planting desirable species, with more frequent rotations between pasture areas.

Livestock may also contribute to soil damage by compacting the ground with their hooves, and by creating trails where gullies may start to form. Sloping ground is particularly vulnerable to erosion started by the frequent passage of animals. In woodland and savanna areas where trees are present, livestock may eat all the tree seedlings, and thus prevent the normal replacement of the trees.

Commercial and subsistence agriculture

Traditional agriculture was almost entirely subsistence agriculture, in which food crops were raised to be eaten locally. Today most agricultural development projects are for commercial agriculture, where the produce is sold to earn money. Such cash crops are becoming increasingly important in rural agriculture.

Commercial agriculture pays best if it is done on a large scale. It often requires the use of machines which are expensive to buy and difficult to maintain. It almost always means using fertilizers and pesticides which cost money and may cause health or environmental problems if they are not used with care. The commercial market requires uniform varieties which may be more vulnerable to an agricultural disaster. All of this means a higher investment which may be difficult or beyond the reach of a small farmer, as well as a greater risk of environmental damage.

Subsistence agriculture is usually based on traditional methods which have proven themselves over hundreds of years. It uses many varieties of trees and plants, usually mixed together in the same garden but with roots at different levels to make full use of the soil while protecting it from erosion. It is done on a small scale making good use of the space available, and is thus better balanced with the environment. It fits local social and cultural patterns, and as traditionally practised usually provided a healthy and balanced if not very varied diet. However, it can present environmental problems if the population is increasing and too much pressure is being put on the land.

What is worse is that too often cash crops are replacing local food crops in rural agriculture. The cash crop requires an important investment, so the best land is used for it; food plants are put on whatever land is left. The first priority for labour is maintaining the cash crop, so less time is available for growing food, and the planting calendar may be changed to less desirable times to avoid conflicting with the requirements of the cash crop. Since less food can be produced under these conditions, the money earned with the cash crop goes to buy imported food. This is often less nutritious than fresh local foods even if it tastes good. Health problems like bad teeth and growing too fat, and sicknesses like diabetes, high blood pressure and heart attacks have become big problems in island countries for people who have changed from traditional to imported food. Children suffer particularly from eating too much sugar, rice, corn pops and soft drinks, and not enough vegetables and protein; they do not grow well and they are often sick.

This does not mean that commercial agriculture is necessarily bad. What is important is that a community must balance its desire for money with the need to provide proper food for its people and to be more self-sufficient. There is no reason why both cannot be done together with some careful planning.

Strategies for agriculture

The differences between modern commercial and traditional subsistence agriculture also illustrate two different strategies which can lead to conflict or failure in an agricultural project if they are not well understood.

A western agriculturalist tries to produce as much as he can. He selects the highest yielding variety and fertilizes it well; he fights off weeds, pests and diseases with the latest chemicals; machines let him plant and harvest quickly and efficiently. If the harvest is good, he covers his costs and makes a tidy profit. If there is a disaster, he requests compensation, or borrows against the next year's harvest and starts again.

Traditional agriculture evolved under different conditions. The first priority was to be sure to always have something to eat. At a time when food aid did not exist, it was essential to minimize the risk of complete failure which meant starvation. A high producing variety might be planted, but so would hardier plants able to resist bad conditions. Traditional agriculturalists are slow to try anything new, because that will increase their risks.

While it is in the long-term interest of all agriculture to preserve the productivity of the land, the short-term interests may be different. The commercial farmer must keep his or her costs down on order to make money, and environmental measures may increase costs or reduce the yield. It is natural to want to put off such measures for some other time if they do not seem too pressing. For the traditional farmer, environmental protection reduces the risk of failure, especially where the risk is greatest from a storm, flood or other catastrophe. Then it is worth while to invest in protective measures, even if it is several years before they show their value.

There may also be a difference between the needs of the individual, for whom the first priority might be to make money for a traditional wedding or to buy a radio-cassette, and the environmental needs of the group or community, for whom preserving the productivity of the land is the best assurance for the future.

Both strategies, of producing as much as possible and of reducing the risk of complete failure, have their place. It is for each community or each individual farmer to find the balance or combination between the two that fits their goals and the alternatives (or lack of alternatives) available to them. A good discussion and conscious decision on these strategies is particularly important where expatriate or western-trained agricultural advisers are working with subsistence farmers. Both the economic and environmental dimensions of these strategies need to be well understood.

It should be clear from the above that sustainable agriculture depends on good environmental management. In practice this is never easy because agricultural systems are very complicated, many environmental factors are unpredictable and cannot be controlled, and there is much we still do not know. However, with an understanding of the principles, confidence in local knowledge, a certain caution, plenty of common sense, and a willingness to work hard, the chances of success are reasonably good.


Why is environmental management important for agriculture?

Is agriculture a renewable resource? What does that mean?

What is the difference between agriculture on newly cleared land and that on land that has been used for many years?

Why are soils important for crops?

What is the role of the weather and climate in agriculture?

What can be done to reduce the influence of climate?

How do biological interactions affect agriculture? (Give specific examples)

How do you select the best varieties for local use?

What does overgrazing do to the land?

How can you tell if pasture is overgrazed?

What is the difference between commercial and subsistence agriculture?

Why have cash crops sometimes led to health problems?

What are the differences in strategy between modern commercial and traditional subsistence farmers?

Instructions for trainers in the use of this unit

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UN System-Wide Earthwatch Coordination, UNEP, Geneva
Updated 7 April 1998