Zambia's agriculture is predominantly rainfed. The major crops grown in the country are maize, sunflower, soybeans, groundnuts, sorghum, cotton, beans, bambara groundnuts, cowpea, sugarcane, finger millet, bulrush millet, rice, sweet potato, cassava, tobacco, and wheat. The main tools for land clearing in Zambia are the machete, hoe, and fire. Cultivation methods are mainly based on use of the manual hoe. Livestock raising is also an important traditional practice in the Southern, Eastern, and Western, and parts of the Central provinces of Zambia, where animal draft power is common. Tractors are mainly used by commercial farmers.
A form of slash-and-burn agriculture and adaptations to it are practiced. In the slash-and-burn chitemene system, tree offshoots from an area 12 times the size of the area to be cropped and the tree limbs and branches are heaped in a circular area in the middle of the field and burned. The ash from the burned wood acts as an ameliorator of soil acidity and supplier of nutrients, mostly P and K. Nitrogen, C, and S are lost in the combustion. The area is used for 3 to 5 years to produce millet and sorghum mixed with legumes and cassava. It is then left fallow for 15 to 20 years to regenerate before it is cropped again (Chidumayo and Chidumayo, 1984).
In Zambia, inversion tillage is the conventional practice, especially for resource-poor farmers. Although inversion tillage has its benefits, it is a major contributor to SOM/SOC loss. This is because the soil is turned over, exposing the SOM to high temperatures and erosive agents that bring the (mostly infertile) subsoil to the surface. Because of high temperatures, SOM is oxidized quickly and lost. This leads to a host of soil quality problems, such as structure destruction, crusting, hard setting, poor transmission properties, and loss of plant nutrients.
Conservation tillage in Zambia started as early as the 1930s (Environmental Conservation Association of Zambia, 1998). A traditional form, known as galauza, is practiced in the Eastern province. At the end of the dry season, the farmers scrape all dry plant residues off the soil and arrange them in a line along old ridges by hand hoeing. Crop residues are placed in the furrows between the previous season's ridges. The old ridge soil is turned over to cover the residues and to form new ridges in the position where the old furrows were located in the past season. Some farmers burn residues before the soil is turned over on them, in which case the beneficial effects of galuza are probably negated, and SOM and SOC are lost.
An adaptation to the chitemene system, due to diminishing woodlands, is the grass-mound fundikila system, where grass is buried in mounds and left to decompose at the end of the rainy season. The mounds are spread open at the beginning of the next rains, and beans, maize, groundnuts, cucurbits, cowpeas, and millet are planted. The land under this system is cropped for about 8 years before it is abandoned for another 8 to 10 years to regenerate.
The chitemene system was able to support 2.8 people per km-2 30 years ago. It now supports 12 to 15 people km-2 (Chidumayo, 1987). The fundikila, which supported 10 people km-2 30 years ago, now supports 20 to 30 people km-2. These systems are breaking down under population pressure, and intervention is needed to rebuild soil fertility.
In the central plateau of the Southern and Eastern provinces, continuous cultivation, improper use of inorganic fertilizers, poor crop residue management, and generally poor land husbandry practices have caused acidity, as well as declines in soil fertility and SOM. Since the best land is already taken, farmers who are under survival pressures must continue farming on the same land.
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