been utilized within the region have also been inadequate and have resulted in low crop quality and productivity.

Typology of cropping systems. Climatic variations, types of cultivated crops, cultural practices, farmers’ production objectives and other biotic and abiotic factors have contributed to a number of farming systems found in SSA (Dixon et al., 2001). Cropping systems in SSA are classified according to a number of specific features, such as water supply, type of rotation, cropping pattern and animal activities, degree of commercialization and tools used for cultivation (Ruthenberg, 1980).

Classification according to water supply. In classification according to water supply, two main types of farming are distinguished, namely irrigated farming and rain-fed farming. Most of the farming in SSA is rain-fed, although limited irrigation farming is practiced for a few crops such as rice and some horticultural crops. Most rice production in SSA, both upland and swamp rice, has been rain-fed. Other crops grown under rain-fed farming include cotton, cassava, sorghum, groundnuts, soybeans, sesame, yams, maize, bananas and plantains. An important part of crop production in SSA occurs on wetlands in valley bottoms and lowlands where water is captured without artificial irrigation.

Classification according to type of rotation. Various natural fallow systems are practiced in SSA, whereby cultivation alternates with an uncultivated fallow and may take the following forms: Forest fallows comprised of woody vegetation and closed canopies, in which trees are ecologically dominant; bush fallows comprised of thick vegetation in which shrubs are ecologically dominant; savanna fallows comprised of a mixture of fire-resistant trees and grasses; and grass fallows, comprised of grasses without woody vegetation.

Classification according to cropping pattern. There are two main types of cropping patterns, mixed cropping and monocropping. Mixed cropping with different crops grown at the same time in a given field is common in SSA with differences in technique. Mixed cropping appears to be the more effective way of reducing the risks of hunger and ensuring food security as it has the advantage of crop diversification (Ruthenberg, 1980). The common mixed cropping found in SSA are legumes/cereals, coffee/fiber crops, legumes/fiber crops.

          Monocropping is practiced mainly in commercial farming and has the advantage of increased yield of particular crops. For instance, increased cowpea production has been obtained over the years due to a change from the traditional intercropping system to monocrops of cowpea and strip cropping involving two rows of cereals and four rows of
cowpea (Singh and Ajeigbe, 2002). This improved intercropping system minimizes shading from the cereals crops and maximizes gains from limited application of fertilizer and agrochemicals.

Classification according to degree of commercialization. Three broad classifications are used: subsistence farming;

partly commercialized farming; and commercialized farming. In SSA, 70% of agricultural production is subsistence farming and little commercialized farming occurs.

Classification according to implements used for cultivation. The three main classifications are: hoe-farming; farming with ploughs and animal traction; and farming with ploughs and tractors. Most of the subsistence farming in SSA is done by hoe-farming, but in some cases ploughs and animal traction are used as well. Commercial farming is done by ploughs and tractors.

Examples of Major Food and Cash Crops in SSA

Groundnut. Groundnut (Arachis hypogaea L.) is important both as an earner of foreign exchange as well as a source of good quality food. Groundnut is a leguminous oil crop, of high nutritional value, containing about 25% protein and 40 to 45% oil (Harkness, 1970). It is the most important source of vegetable oil and fat in SSA. Groundnut is thus a vital source of energy and contributes to dietary protein available for the control of various protein-deficiency diseases in the region. It is consumed in various forms in SSA including groundnut oil, roasted groundnut, oiled or raw groundnut and as ground or paste. Groundnut production in the SSA before the 1960s was low due to farmers growing the crop with minimum inputs using traditional local groundnut varieties as a component of mixed cropping systems. This trend continued in the region until the 1960s when, due to improved crop management practices and increase in harvested acreage, groundnut production increased to export levels. Groundnut production in SSA increased in the 1960s up to 1970. While world groundnut production continued to increase from the 1970s to the 1980s, SSA had a 17% decrease in production, with eastern and southern Africa being the main contributors to this loss due to changes in harvested area (-13%) and yield (-5%) (Fletcher et al., 1992). This trend has continued to the present.

          The decline in production in SSA has been due to nonadoption of improved groundnut varieties, untimely and inappropriate use of farm inputs, low plant population and poor crop husbandry (Schilling and Misari, 1992). Decline in groundnut production can also be linked to low world market price because of substitution by soybean and sunflower oil. Other factors include unfavorable climatic conditions characterized by frequent droughts, high temperature and a decline in soil productivity due to continuous cultivation. Increases in grain yield have resulted from the use of pest resistant and high-yielding varieties and appropriate cultural and pest control measures.

Maize. Maize (Zea mays L.) is one of the most important staple foods in SSA. It is also one of the cheapest sources of energy readily available to poor people and rural dwellers in SSA. The grain contains 79% carbohydrate, 9% protein and 4% fat (NRC, 1979). Maize is also in high demand for livestock feed and for production of alcohol in the brewing industry. It serves as a raw material in textile and paper industries.