|Sustainable Agriculture and the Environment|
For the most part of human history, people have satisfied their food needs by hunting and gathering. Although the hunter-gatherers use of fire may have impacted the environment to a small degree, this is nothing compared to how subsequent farmers affected their ecological surroundings. Agriculture inevitably transforms the land, but in what ways it does so depends upon what type of agriculture, what system or model of agricultural production is employed.
Farmers continuously have to make choices about what to plant, how to plant, when to plant, and what to plant. Together, these decisions will influence what type of farming system the farmer in question establishes. Decisions that farmers make will depend on the 'sign of the times', natural, cultural and economic conditions will inevitably change as time passes by, and this inherent change will give rise to a continuous evolution of agricultural systems. Typically, such evolutionary changes involve the intensification of production systems. Geography very much influences the types of systems that evolve, and we will look at what types of systems are to be found in which geographical regions, and do such regional systems share any distinguishing features.
Agricultural production systems show a tremendous variation throughout the tropics. They are hardly ever stable, but are constantly changing. Obviously, the conscious choices made by farmers on how to fashion their mode of tilling, sowing, harvesting, etc as well as what inputs to use, influences the systems that eventually are established. What, then, are the factors influencing a farmer's choice of a particular system? The most important factors identified may be categorised into three major classes: the political/economic frame conditions, the household characteristics, and the natural resource base. The figure below depicts the factors influencing farmers' choice of production systems, and the relationship between farmers' choices and environmental effects.
Figure 1. Farmers' choice of production systems
1. The political/economic conditions are generally outside the control of farmers, and are determined by national and regional policies, international markets, and trade regulations. Conditions of particular importance are prices of inputs and outputs, markets, infrastructure, and land tenure systems. Farmers' decision making will also be influenced by the capacity of the extension service, and access to new technology through research. Political unrest and wars are events that strongly influence farmers' decision making. The more farmers are integrated into markets, the more the political /economic frame conditions are important. Peasants are typically less integrated into the market than commercial farmers.
2. The second major class of factors which influence farmers' decision making is the household characteristics. Labour and land availability, consumption needs and food preferences, capital assets, knowledge base (literacy/traditional knowledge), religion, off-farm income, and willingness to take risk are all important factors which will influence household decision making. Poor families with few capital assets (animals, etc.) will in general be less willing to take risk. Farmers with a good knowledge base can more easily take part in market activities, and can more effectively make use of extension services and new technologies.
3. The natural resource base is the third major class of factors which influence farmers' decision making. Some of these natural resources are outside the control of the farmer, such as climate and water for irrigation, whereas the farmer can to some extent control soil quality and farm genetic resources. Farmers need to consider the quality and quantity of these resources when decisions are made.
The household production objectives, together with an assessment of the political/economical frame conditions, the household characteristics, and natural resource base, will form the basis for households' decision making. Households differ with regard to production objectives. Poor households will, in general, be more subsistence-oriented, while better-off households will be more cash and profit-oriented. The interest to maintain the farm resources will also differ between households. The key decisions households make with regard to agricultural production is on what to produce, how to produce, and how much to produce. Different households make different decisions due to variation in household characteristics such as labour availability, access to capital, off-farm income, etc. The sum of decisions of all households will determine the amount of products offered on the market, and the relationship between supply and demand of products will, in a free market, determine the price of products. This is one of the feedback mechanisms shown in figure 1.
The decisions farmers make with regard to what to produce and what type of technology to use will have environmental consequences. The sum of all farmers' decisions will determine the quality of the future land resources. The choice of agricultural technology can, for example, determine the degree of soil erosion, water pollution, and carbon emission. There is a feedback mechanism between these processes and the quality of the natural resource base.
Agricultural production systems will change over time due to changes in the political/economic conditions, household characteristics, and the natural resource base. Decision makers can influence the development of tropical production systems through price policies, interest rates, land tenure legislation, extension, and research.
Figure 2 shows an example of such a gathering system from Mali that is still existing. In this case, harvesting is done by brushing the ground after ripe seeds of the Fonio (Panicum laetum) seed have fallen to the ground. The fonio is not sown, but regenerate each year by natural regeneration, and hence represents a gathering system, not an agricultural production system since the seeds are not planted manually. Gathering systems such as this, although rare, are not a thing of the past although one might be induced to believe so when reading about current modern agricultural practices.
As population density increases, gathering will seldom suffice to feed all, and rural dwellers would often tend to take up agricultural activities and establish themselves as farmers. The first type of agriculture introduced is normally different forms of 'slash and burn' agriculture or fallow systems. Farmers burn the vegetation and cultivate the land for some years. The effect of burning is to add plant nutrients, increase soil pH, and reduce weed infestation. However, yields will decline during the first years of cultivation due to increased weed infestation and loss of soil fertility. When the yield becomes too low, the land is returned to fallow for a period of time before it once again is cleared and burned. This type of agriculture is found under low population densities and is still practised in parts of humid and sub-humid areas.
Fallow systems may subsequently develop into permanent agriculture. There is generally a strong relationship between farming intensity, population growth, and agricultural mechanisation. Fallow systems dominate when population density is low, whereas annual cultivation will only appear in more densely populated areas (see table).
Table 1) Relationship between farming system, intensity of farming and population density (Pingali et al., 1987)
The R-value is 100 if there is one cropping cycle per year
Agricultural intensification implies an increased frequency of cultivation. Other features of agricultural intensification are transition from hand-hoe to the plough, an increase in investment for destumping, terracing, use of manure, and a change from general use rights to specific land rights.
The following factors have been found to effect the shift from a fallow system to a more intensive system:
The cost of moving to new land will typically be lower for smallholders and peasants than for large scale farmers. Large scale/mechanistic farmers will clear the land completely for roots and stones, whereas small scale farmers normally do not destump the trees. Clearing the land of roots and stones will also make it more easy to introduce animal traction for ploughing. Animal traction is for this reason seldom practised in fallow systems. Moreover, large-scale farmers may have more easy access than peasants to purchased inputs useful for maintaining soil productivity. Fallow systems are therefore more attractive to smallholders and peasants than to larger-scale farmers.
Major agroecological zones of the tropics are arid, semi-arid, sub-humid, humid and highland areas. There is, in general, a strong relationship between agro-climatic conditions, population density, cropping systems, and livestock production (please see table 2). Animal grazing systems will also differ between arid, semi-arid, humid and highland areas.
Arid areas are characterised by low population density, and nomadic livestock systems are often practised A nomad is highly mobile, but does not necessarily return to the same base every year. This high level of mobility is needed, as there is a tremendous variability in rainfall across space and time. A nomad does not usually grow crops, as arid areas are often too dry for rainfed agriculture. However, agriculture and gardening may be practised in the proximity of an oasis.
The semiarid tropics is characterised by permanent agriculture, and livestock production is often a mix of transhumance and sedentary livestock production. The natural vegetation is various forms of savannahs. Agropastoralism is common under semiarid conditions. Agropastoralism comprises a range of adaptations from some minor annual planting of a cereal combined with a predominantly pastoral way of life, to a closely integrated system of crops and livestock on a permanently settled farm (mixed farming). Mixed cropping is important in semiarid tropics, sub-humid and highland areas. Cereal crops like pearl millet and sorghum are important crops. Cereals are ubiquitous crops in semiarid, subhumid and highland areas, because they can be easily stored and traded. Cereal systems, therefore, allow wealth accumulation and is for this reason one of the fundaments for old civilisations. Other important crops in semiarid tropics are grain legumes like e.g. cowpea and groundnut. Cereals combined with grain legumes constitute a diet of very good quality.
Soils in semiarid tropics are often poor in nitrogen and phosphorous. Farming in semiarid areas is characterised by relatively low response to inputs, high erosion rates, and erratic rainfall which often causes extreme variation in yield. In the Sahel, the livestock herders bring their animals to fields belonging to farmers after harvest. The animals feed on the crop residues and leave manure for the benefit of further crop production. The parasitic weed striga often causes problems in semiarid regions and problems are more severe in areas with low soil fertility. It is a very difficult weed to control because the seeds can remain dormant for many years in the soil, and because it attacks the most important crop species in the semiarid tropics. In addition, it a has a high ability to adapt to new resistant varieties. Various measures for controlling striga has been developed. Various types of traditional agroforestry systems is often practised in semiarid areas. One of these systems is pearl millet and the tree Acacia albida, which sheds its leaves in the dry season and fixes nitrogen, and thus is well adapted to the climatic conditions.
Sub-humid areas probably have the best conditions for agriculture, and population density is for this reason high. More plant species are grown in these areas, and cropping systems are often more complex. Maize and rice are major crops in sub-humid areas. Tuber crops like cassava and sweet potatoes are more frequently found in this region as well, as compared to the more arid zones. Different crops are often combined on the same piece of land in mixed cropping systems, which are often associated with subsistence production. Intensification of mixed cropping is difficult due to problems with mechanising the production, and applying the correct amount of inputs. Crop rotation systems can provide many of the same benefits as mixed cropping systems. Livestock production is mainly sedentary in sub-humid areas.
The natural vegetation in humid tropical areas is in most cases lush rainforest. Most of the plant nutrients are absorbed in the vegetation, and not in the soil. Soils in the humid tropics are often leached, resulting in acid soils with problems of aluminium toxicity. Major crops in the humid tropics are maize, tuber crops , rice , plantains, and tree crops such as oil palm. Local peoples in such areas have developed three different production systems that, in the traditional form, have proved to be sustainable: (1) Shifting cultivation, (2) Permanent home gardens, and (3) Lowland rice production on submerged soil.
1. In shifting cultivation, the vegetation is cleared by felling of trees, burning, and planting of crops for a short period, most often only for one year. After harvesting the planted crops, the land is left for natural regeneration and quickly forms secondary forest (see above).
2. The permanent home gardens are structured as multistorey cropping systems. They replace natural forests with unsubsidised nutrient cycling and may function well if most of harvested production is for subsistence and when the waste is returned to the cropped land. In home garden multistorey systems this is frequently the case. The home garden receives all household waste and may also serve as field latrine or site for shifting latrines. In this way, nutrients are returned to the land from which they are taken.
3. There exist several forms of lowland rice production. Traditional wet-rice cultivation exploits natural flooding during summer rains (monsoon climate). Local varieties are normally sensitive to the day length (photoperiod). In that way growth, flowering and seed maturation is timed according to the season of normal flooding. That system is classified as “rainfed lowland”. We also have deep water or flood-prone rice systems; from a half to several metres of inundation (also season dependent). That cultivation system is found in river basins mainly in South and Southeast Asia, but also along the Niger River in West Africa. The modern intensive form of rice cultivation is called “irrigated rice” and assumes a water management that can assure optimal flooding (about 5 cm) throughout the growing season(s), often long enough to allow double cropping. With year-round continuous submersion more than two crops is possible. In the Mekong Delta in Vietnam, some farmers manage 7 crops of rice in a two-year period. Such cultivation requires day length-neutral (non-photoperiodic) varieties to allow normal crop development independent of the season. Hybrid rice has been developed. Yields are higher, but it requires farmers to change seeds every year.
Livestock density is low in humid areas due to prevalence of livestock pests, particularly in Africa. Trypanosomiasis, which is transmitted by the tsetse fly, is a major threat to livestock in the forest fallow and bush fallow systems. The reason is that the tsetse fly is shade-loving, and can only survive under forest bush cover. Pest and diseases often cause serious losses in humid areas. Storage of agricultural products is another serious problem in the humid tropics.
Most highland areas have a high population density. Important crops are wheat, maize and barley in addition to grain legumes. Coffee and tea are important cash crops in humid highland areas. More livestock is found in the highlands and mixed cropping is practices, and animal traction is more widely used. Nomadic livestock systems are found in the highlands of Central Asia.
Table 2. Characteristics of major agroecological zones in sub-Saharan Africa (Powell and Williams 1993):
This lecture shows that there is a tremendous variation in the type of agricultural production system practised in the tropics. It has been shown that farmers make their decision based on political /economic frame conditions, household characteristics, and the natural resource base. These factors, together with household production objectives, form the basis for household decision making. Households decide on what to produce, how to produce, and how much to produce. These choices will have environmental consequences, and will determine the quantities and quality of the products offered on the market.
Questions for Reflection
What are the features of agricultural intensification?
Why is it difficult to introduce improved agricultural practices in areas with low R-values?
McCalla, Alex F. 'Agriculture and Food Needs to 2025' The article is taken from
the book 'International Agricultural Development' (1998) edited by Carl
K. Eicher and John M. Staatz, Johns Hopkins University.Press.
McCalla, Alex F. 'Agriculture and Food Needs to 2025'
The article is taken from the book 'International Agricultural Development' (1998) edited by Carl K. Eicher and John M. Staatz, Johns Hopkins University.Press.
You are now ready to go on to Lecture 2, on Soil Fertility Management.