"It was only when we stopped using fertilizer that we realized something bad was happening to our soils." Several small-scale Malawi farmers during a 1997 survey1."
Many of today's most pressing problems for rural people and their environments are related to the management of land and water resources. They include malnutrition, food insecurity, low standards of living, large-scale migration and sometimes violent competition for resources to satisfy basic needs. Environmental concerns include land degradation, destruction of terrestrial and aquatic habitats and loss of biodiversity.
The human population, which doubled in the last forty years, is expected to double again within the coming half century. The increase will occur mainly in poor countries with few resources and unstable conditions for production. Therefore, social and political repercussions will be proportionately greater.
While populations continue to increase, the availability of non-renewable resources per person will clearly decline. Another issue of increasing importance is the prevention of environmental contamination by minimising waste from production and marketing processes, and safe disposal or reuse of waste products.
The primary source of food for humans and animals is based upon plants. Except for carbon, which enters plants through the leaves, all the elements necessary for plant growth, human and animal nutrition are obtained from the soil via the plant root system: nitrogen, oxygen, phosphorus, potassium, calcium, etc.
Due to population concentration and pressure, these elements are drained from soils into city sewage and landfills. A crude calculation shows that the daily dietary requirements of phosphorus for a world population of 5.5 billion people annually requires about 1.4 kg of phosphorus from each hectare of the 1.5 billion hectares of cropland in the world. No soil, regardless of its initial mineral composition, can continue to have food products exported from it indefinitely without active support.
Many agricultural systems are found around the world, such as intensive cropping systems, shifting cultivation, agroforestry, etc. (Annex 1). In conventional agriculture, the soil is frequently regarded only as a substrate that provides physical support, water and nutrients to plants, and it is assumed that farmers must supplement all plant needs (such as nutrients, protection, water) with external inputs:
Some of these practices may be necessary, under specific conditions and appropriate planning, monitoring and management. However, some common practices may lead to serious problems for the human being and the environment (Table 1).
Common practices and consequences of conventional agriculture
Removal or burning of crop residues
Continuous ploughing and harrowing
Excessive use of fertilizers
Misuse of pesticides
Misuse of water
Loss of soil fertility and decreasing yields
Increased drought and flood risks
Food insecurity and health risks
Contamination of ground and surface water
Contamination and degradation of soils
Greenhouse gas release
Loss of biodiversity
In conventional agriculture, soil tillage is considered as one of the most important operations to create a favourable soil structure, prepare the seedbed and control weeds. But mechanical implements, particularly those drawn or driven by tractors (Plate 1), destroy the soil structure by reducing the aggregate size, and currently conventional tillage methods are a major cause of soil loss and desertification in many developing countries.
Continuous cultivation damages the vital but fragile ecosystem of soil flora and fauna, Bolivia. [R. Jones/FAO/19376]
Tillage-induced soil erosion in developing countries can entail soil losses exceeding 150 t/ha annually and soil erosion, accelerated by wind and water, is responsible for 40 percent of land degradation world-wide.
The increased mineralisation of soil organic matter resulting from continuous cultivation may bring short-term yield increases, but in the long term the soil life and the soil structure are damaged. Deep tillage is harmful to earthworms and other soil organisms. It can kill them outright, disrupt their burrows, lower soil moisture, and reduce the amount and availability of their food. Other inappropriate land management practices, such as the use of certain pesticides (for example aldicarb, carbaryl, carbofuran, benomyl, and most soil fumigants) and some inorganic fertilizers, especially ammonium sulphate, can also be harmful to soil life. All these practices result in declining soil life and organic matter which are important for oxygen, water and nutrient cycles, including moisture retention, water infiltration and plant nutrition.
The soil then becomes vulnerable to compaction, which in turn reduces water infiltration rate and storage capacity. One of the results is an increased water flow across bare soil inducing run-off and water-borne soil loss and further loss of potential productivity.
Continuing soil degradation is threatening food security and the livelihood of millions of farm households throughout the world. The main causes include not only intensive soil preparation by hoeing or ploughing, but also deforestation, the removal or burning of crop residues, poor rangeland management and inadequate crop rotations that do not maintain vegetative cover or allow appropriate restitution of organic matter and plant nutrients. These practices leave the soil exposed to climatic hazards such as wind, rain and sun.
Thus, the intensive and continued use of the plough has proven to be unsustainable in several climatic zones. Many farmers have been induced to reconsider ploughing and its effects. Conservation tillage systems were developed to protect the soil and reduce erosion. Economic pressures in some countries also led to the development of minimum or reduced tillage systems. A common feature of these systems is the elimination or the minimal use of the plough. Soil tillage may still be used to loosen the soil and to mix soil components, but chisel tines are preferred, leaving most of the crop residues on or close to the soil surface and not exposing the bare soil to wind and rain.
Box 1: Principles of conservation agriculture
The goal of conservation agriculture is to maintain and improve crop yields and resilience against drought and other hazards, while at the same time protecting and stimulating the biological functioning of the soil.
Two essential features of conservation agriculture (Box 2) are no-tillage and the maintenance of a cover (live or dead vegetal material) on the soil surface. Crops are seeded or planted through this cover with special equipment. However, although no-tillage is an essential feature of conservation agriculture, the use of no-tillage by itself does not qualify for conservation agriculture. As long as a farmer ploughs for at least one crop within the rotation or does not maintain a permanent soil cover, he does not practise conservation agriculture.
The soil cover also inhibits the germination of many weed seeds, minimising weed competition with the crop. In the first few years, however, herbicide may still need to be applied, making a location-specific knowledge of weeds and herbicide application important. Conservation agriculture also involves planning crop sequences over several seasons, to minimise the build-up of pests or diseases and to optimise plant nutrient use by synergy between different crop types and by alternating shallow-rooting crops with deep-rooting ones. The continuous use of the cropland is allowed.
Sustainable intensification of crop production is possible in currently unimproved or degraded areas. Empirical evidence has been accumulating that low (but not necessarily zero-) input agriculture can be highly productive, provided farmers participate fully in all stages of technology development and extension. This evidence indicates that the productivity of agricultural and pastoral lands is a function of human capacity and ingenuity as much as of biological and physical processes.
This has led to what is called "conservation agriculture" (Box 1). Three criteria, which are interrelated, distinguish conservation agriculture from a conventional agricultural system: reduced or zero tillage, permanent soil cover and crop rotation. The biomass produced in the system is kept on the soil surface rather than incorporated and serves as a physical protection of the soil and as substrate for the soil fauna. In this way mineralisation is reduced and soil organic matter is built up and maintained. Mechanical tillage is avoided in order to maintain the existing interactions between soil flora and fauna, which are necessary to liberate plant nutrients. A varied crop rotation is important to avoid pest and disease problems and improve soil conditions.
Key features of conservation agriculture systems are listed in Box 2.
Box 2: Key features of conservation agriculture systems
A growing number of experiences of the benefits of conservation agriculture in both mechanised and non-mechanised agriculture, on tens of millions of hectares of small and large farms in both temperate and tropical zones, suggest that further significant improvements in conservation-effective agriculture are indeed possible. These will be acceptable to farmers if they are cost-effective in the short term.
The conservation agriculture systems discussed in this report have proven to be effective in exploiting the natural resources upon which they are based without degrading them, and in some cases allowing their restoration. Each case brings out the interactions and complementarity that exist between sound scientific and practical knowledge, market factors, social and political contexts, and public policies and investments. The cases discussed are examples of the wide range of circumstances found in Latin America (Plate 2) and Africa. All are of rainfed farming and cover a range of low-income and lower-middle income countries with contrasting physical and economic conditions. The set of cases covers only small-scale farm operations. Some have developed in response to macroeconomic and market changes, often changes in physical and social infrastructure have been important, but in all cases a necessary condition for change has been that the underlying physical, chemical, and biological systems have been understood and respected by the farmers.
Soybean grown under conservation agriculture in Brazil
Conservation agriculture has evolved from the zero tillage technique. Zero tillage or no-tillage system is based on the use of crop residues or mulch as a surface cover, and the improvement of the natural cycles in the soil. With time, soil life takes over the functions of traditional soil tillage, loosening the soil and mixing the soil components. But in addition to that the increased biological soil activity creates a stable soil structure through accumulation of organic matter.
The pioneers started to practise zero tillage as a form of conservation tillage on their farms in the early sixties and seventies in the USA and Brazil respectively. Initial adoption was slow, but since the mid-1980s its spread has been rapid, especially in the Americas and Australia. (Table 2).
Conservation agriculture based on zero tillage has proven especially useful for maintaining and building up soil organic matter and improving soil fertility, primarily through reducing soil disturbance, conservation of the soil structure and stimulating soil biota. Information on the soil ecosystem is provided in Annex 2.
Total area - in hectares - under no-tillage in different countries in the seventies, eighties and in1999/2000 (Derpsch, 1999 modified by Benites)
Japan, Malaysia, Sri Lanka
2 200 000
4 800 000
19 750 000
4 080 000
8 640 000
13 470 000
9 250 000
1 Evans et al., 1999