|Environmental Handbook Volume II: Agriculture, Mining/Energy, Trade/Industry (GTZ, 1995, 736 p.)|
|27. Plant production|
In agroecosystems, man becomes the dominant element in the ecosystem (anthropogenically oriented ecosystems). Agroecosystems differ in particular from natural ecosystems in that natural regulation processes take second place to control by man.
In the natural environment, plants form part of the ecosystem and play a key role in preserving it. Depending on the cropping method used, the nature, intensity and interaction of cultivation measures give rise to specific environmental impacts. These may cause a reduction in the diversity of species, disruption of the soil structure and pollution of the soil, water and air (pesticides, salts resulting from irrigation and fertilisation, nitrate etc.) Natural ecosystems with their wide variety of functions are replaced by artificial land-use systems poor in species.
Growing use of industrially produced inputs (fertilisers, pesticides, machines, energy) and inappropriate cultivation techniques lead to contamination of drinking water by fertilisers and pesticides, as well as causing soil erosion, desertification and genetic erosion.
2.1 Environmental impacts
Soil forms the basis for plant production and thus performs a vital function in guaranteeing human survival.
Soil conservation is essential if man's living environment is to be maintained in a healthy state and a sustained supply of high-quality foods is to be ensured.
Opportunities for changing the conditions prevailing on a particular site are limited. Cultivation measures must therefore be geared to the natural conditions under which the land is used.
Erosion - in other words the removal of soil by water and wind - is one of the most problematic consequences of agriculture, particularly in the tropics.
The actual extent of erosion depends on the type of crop and form of cropping. To minimise erosion, efforts should be made to ensure that there is ground cover all year round. In the case of monoculture and single cropping, the risk of erosion becomes greater the more slowly the young plants develop (e.g. maize, grain legumes), the lower the planting density is and the more comprehensive the weed control measures are. As annual crops such as cereals, tubers and grain legumes entail frequent tillage, they have an adverse effect on the soil structure and are thus conducive to erosion.
Perennial crops such as fruit trees generally prevent soil erosion once the stand is complete; they provide permanent shade, which has a positive effect on the soil structure.
A soil's erodibility depends among other things on its physical properties. Fine sand and abraded particles can be displaced most easily, whereas a high stone and clay content inhibits erosion. A high humus content stabilises the soil structure and increases the water storage capacity; both of these factors inhibit erosion.
The most important ways of controlling erosion are:
- adequate ground cover (intercropping, underseeding etc.);
- "storeyed" cultivation through integration of trees and shrubs;
- division of cropping areas into small units and creation of windbreaks at right angles to the direction of the prevailing wind;
- avoidance of overstocking and measures to prevent animals from grazing on newly sown areas (see environmental brief Livestock Farming).
Excessive mechanisation of tillage and harvesting can lead to compaction, plough sole formation and puddling, particularly in the case of tropical soils with a weak structure. This may have the adverse effect of reducing water infiltration and the air supply for the soil flora and fauna as well as for the crops. Mechanisation can also lead to changes in the division of labour between men and women.
Although frequent tillage generally has a stimulating effect on microbial activity and thus also on replenishment of the nutrient supply, it has disadvantages in the tropics:
- humus decomposition is excessively rapid on account of the
- the soil fauna are adversely affected and formation of new humus is thereby delayed.
Single cropping promotes the spread of pests on a large scale and tends to necessitate substantial use of pesticides. Introduction of pesticides into the soil has adverse effects on the soil fauna and flora.
Organic matter plays a major role in the dynamics of tropical soils. It stores water, provides a living environment for soil organisms, promotes structural stability, and both supplies and stores nutrients. It is above all in storing nutrients that organic matter performs an especially vital function, as tropical soils seldom contain high-quality nutrient-fixing clay minerals. Use of mineral fertilisers therefore depends on the proportion of organic matter in the soil. If the amount of fertiliser used is not in correct proportion to the organic matter, there is a danger of leaching and of the fertiliser passing into deeper soil layers. Use of too much fertiliser is thus ecologically undesirable and economically disadvantageous.
The risk of unbalanced nutrient depletion is greatest in the case of monoculture and single cropping, e.g. in the case of maize, cocoa, root crops and tubers. Where a number of plant species are grown in an intercropping or crop rotation system this risk becomes smaller, as differing nutrient requirements have to be met. As such forms of cropping incorporate plants with different root systems (shallow, deep) and nutrient requirements (high, low), competition for nutrients, water and light is substantially reduced.
The erosion referred to above can lead to eutrophication of bodies of water through the introduction of nutrients, e.g. liquid manure and nitrate, and to contamination with toxic pesticide residues.
The climate in multi-storeyed stands growing in an intercropping system is better i.e. more balanced, than that in stands of annual crops forming a monoculture or single cropping system. The wind velocity is lower and thus better for crops susceptible to the wind (e.g. bananas).
Air pollution caused as a result of plant production stems primarily from chemical plant protection measures. Evaporation of ammonia during application of solid or liquid manure has hitherto been of only minor significance. Under tropical conditions (high temperatures, low soil sorption capacity), up to 80% of the total nitrogen may evaporate.
Pollution of the air and atmosphere is caused by waste gases resulting from use of machinery, slash-and-burn techniques and burning-off of crop residues, as well as by discharge of gases such as methane and nitrous oxide by swamp rice and large herds of cattle. These factors play a part in the greenhouse effect.
The risk of both the loss of species and a change in the balance of species increases in proportion to the intensity of plant production activities. Controlled shifting cultivation - observing the necessary fallow periods - encroaches least on the natural environment in terms of area if only level areas are cleared on a selective basis. This helps not only to preserve the forests, particularly the rainforests and their resources, but also to protect forest-dwellers, who often possess know-how about things such as plants with potential pharmacological uses and the ecological interrelationships within their living environment.
Systematic cultivation of crops and the related mechanical and chemical forms of weed control cause wild plants to be largely displaced, leading to a reduction in the number of species.
In regions subject to periodic droughts, large-scale cultivation of certain woody plants in a monoculture system substantially increases the fire risk. In addition to nutrient and leaching losses, this can also result in unwanted destruction of grass and tree species not resistant to fire.
Displacement and destruction of plants leads to a reduction in biological diversity. Extensive use of rainforests also substantially reduces the variety of animal species, e.g. in the case of primates and birds.
Natural ecosystems are adversely affected not only by land being required for plant production but also by being broken up (e.g. by traffic routes), which can result in a loss of stability.
Use of land for plant production generally leads to the loss of forest, dry, wet and aquatic biotopes and causes the landscape to take on a uniform nature, e.g. as a consequence of land clearance, drainage, levelling and irrigation.
By comparison with the natural vegetation, plant production destroys habitats and reduces regional diversity. Standardisation of products for the market and breeding to obtain specific traits (e.g. yield, shape, colour) play a part in the loss of local varieties (genetic erosion).
2.2 Protective measures
2.2.1 General conditions
Plant production is influenced to a particularly large extent by general conditions; these may relate not only to climate but also to national (e.g. land ownership situation) or international (economic relations) factors.
Many climatic and vegetation zones are highly sensitive to interference by man, whose activities generally destroy the vegetation, as in the following cases:
- clearance of the tropical rainforest in the Amazon basin for
the purpose of obtaining high-grade timber
- slash-and-burn land clearance by arable farmers in Nigeria's tree-studded savannah, where the transition to permanent cultivation no longer allows the land the opportunity to regenerate
- overgrazing in the Sahel zone as a result of overstocking with large numbers of livestock which remove the already sparse vegetation.
The consequences are disastrous, not only in the humid tropics but also in places which receive less rainfall. As there are virtually no plants left to provide ground cover, the soil undergoes changes within the space of a few years; a key role is played here by the increased decomposition of organic matter in the soil and the fact that the introduction of new organic matter is reduced to a minimum.
Within the existing world economic order, the terms of trade for the countries concerned have steadily deteriorated. It is above all these countries which have been hit by the increased cost of energy and finished products. International agricultural policy likewise does nothing to ensure balanced promotion of plant production.
Rapid population growth means that farms are becoming increasingly small and the land is thus being used more and more intensively. Farms in Latin America today already have an average size of only 2.7 hectares; those in Africa on average cover 1.3 hectares, while the corresponding figure for Asia is less than one hectare. What is more, 10% of persons deriving their living from agriculture in Africa, 25% of those in the Middle East and 30% of those in Latin America own no land at all. Two thirds of those who do possess land own only a tiny area and cannot afford capital-intensive technical inputs such as pesticides, herbicides and mineral fertilisers.
As land becomes increasingly scarce, farming systems undergo a transition from shifting cultivation to semi-permanent and eventually permanent arable farming. This process has already been largely completed in Asia, while in much of Africa and Latin America it is still under way. The changeover to permanent arable farming means that there are no longer any fallow periods (forest, bush, pasture) which allow the soil to regenerate; soil fertility declines and eventually remains at a fairly low level permitting only substantially smaller yields. The shortage of land also necessitates use of areas such as slopes at risk from erosion and thus contributes to environmental degradation.
The relative importance of the crops grown also changes. In the humid and semi-humid tropics the cultivation of yams, sorghum, and maize declines in significance, while crops such as cassava and sweet potatoes become more important. The last-mentioned crops produce relatively good yields even on poor sites, but at the same time cause the soil to become exhausted more quickly.
In many countries, both intensification of agriculture and the industrialisation process are having increasingly adverse impacts on the environment. Waterlogging, salinisation and sedimentation cause the irrigated cropping areas - often created at considerable expense - to lose their fertility after only a few years, which gives a rise to a considerable drop in yield. Traces of persistent pesticides are being increasingly found in bodies of surface water and groundwater reservoirs. The past decade has seen a sharp rise in the number of people suffering pesticide poisoning, while at the same time there has been an enormous increase in the number of pest species resistant to the commonly used pesticides.
The factors described here are generally to be found wherever efforts are being made to raise yields through targeted, conventional modernisation of agriculture. However, such problems are not simply consequences of large-scale agricultural projects, but also arise as the cumulative result of numerous activities on the part of smallholders.
As the actual environmental costs have little or no impact from the farm management viewpoint, there is no incentive to take measures aimed at conserving natural resources or producing sustained improvements in efficiency. Land law, taxation policy and subsidisation policy, along with ascertainment of the external costs involved in production and consumption, are areas which the state must tackle in the interest of promoting environmentally oriented plant production.
There are certain concepts, such as that of ecodevelopment, which are based on the necessary integrated approaches. Tried and tested measures such as integrated plant protection, ecofarming and others point the way towards sustainable development.
Ecofarming aims to achieve a high sustained level of productivity on the site in question under "low external input" conditions and at the same time to preserve or recreate a balanced ecosystem.
This applies in particular in densely populated regions with smallholder-based farming structures and under economic conditions which largely preclude use of external inputs (e.g. mineral fertilisers), for in many cases such inputs are economically non-viable, unaffordable or unavailable on account of supply shortages. Intensification of agriculture must therefore be based on more productive use of scarce goods (nutrients, water, energy) and underutilised idle resources (e.g. labour, individual initiative).
The demand for stability and sustainability stems from the obligation of each generation to pass on to future generations an environment that remains capable of guaranteeing the fundamentals of human existence. The demand for productivity coupled with stability is often seen as a conflict of objectives between irreconcilable short-term and long-term (and frequently also between microeconomic and macroeconomic) viewpoints; in most cases it is the short-term microeconomic considerations that prevail. Ecofarming must endeavour to achieve both objectives to an equal extent.
Ecofarming, or "site-appropriate agriculture" as it is also known, involves treating both regions used for agriculture and individual farms as ecological systems. However, the concept of "site" must not be restricted to natural conditions (soil, climate).
Consideration must also be given to economic development (price-cost ratios, incomes), farm-specific conditions (access to factors of production) and the internal forces influencing a farm's operations (self-sufficiency, risk minimisation, preservation of soil fertility). Last but not least, it is essential that man, together with his culture, needs, taboos and habits, be viewed as a component of the ecological system and not as an outsider.
This integrated approach requires a certain degree of geographical differentiation. Agriculture in many countries is affected by a growing shortage of raw materials and energy and by the accompanying rise in prices. This is particularly true of countries which are in debt and possess little foreign exchange. It is thus these countries above all which must develop forms of agriculture that permit a high degree of self-sufficiency (within a self-contained system) and decentralisation (as well as self-regulation) at national and regional level and within individual farms.
The major elements of ecofarming are as follows:
- creation of appropriate vegetation
· inclusion of trees and shrubs in arable farming
· creation of erosion-protection strips parallel to the incline on slopes and planting of hedges to divide a farm into numerous small fields
· afforestation on the poorest and most degraded soils
- intercropping, alternating with intensive fallow
- organic manuring
- integrated livestock husbandry
- improved mechanisation
- supplementary use of mineral fertiliser
- integrated plant protection and selective weed control
The elements listed above are given in order of precedence. As it is impossible to introduce the entire package of measures immediately, this form of classification indicates which measures must be given top priority for the purpose of preserving, increasing and stabilising soil productivity.
The following key areas of activity and options in the plant production sector should be combined with one another according to the nature of the site:
- farm planning and organisation (information systems, economic
thresholds, soil investigations, climatic data)
- design of cropping system (single cropping, intercropping etc.)
- variety and seed selection (resistance, quality, quantity)
· minimum tillage
· direct drilling
- cultivation and land use (crop rotation, sustainable cropping
- plant nutrition (fertilising)
- plant protection
To sum up, it can be said that environmentally sound, site-appropriate agriculture aims
- to guarantee that plant production is geared to natural
conditions, i.e. site-appropriate;
- to preserve the soil structure, the biological processes taking place in the soil and the soil's fertility;
- to prevent erosion damage;
- to prevent contamination of groundwater and bodies of surface water;
- to prevent adverse impacts on biotopes adjacent to agricultural land as a result of the introduction of substances or other consequences of cultivation measures;
- to preserve typical landscape features;
- to take account of the requirements of nature conservation and protection of species, particularly as regards preservation of ecologically valuable biotopes, within the scope of overall consideration of the environment;
- to make livestock husbandry an integral component of environmentally sound agriculture.