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Rainfed agriculture and cropping systems on Vertisols in Sudan

M.A. Mahmoud

Agricultural Research Corporation
Shambat, PO Box 125, Khartoum North, Sudan


Abstract


Abstract

Of Sudan's total cropped land area of about 7.4 million ha, some 4.1 million ha (more than 55%) are Vertisols. Only about 825 000 ha of Vertisols are under irrigation; rainfed agriculture on Vertisols thus occupies some 45% (3.3 million ha) of the country's total cropped area. This rainfed area is farmed by traditional methods (about 900 000 ha) or mechanised systems (about 2.4 million ha). In both sectors, sorghum and sesame are virtually the only crops, occupying about 2.8 million and 400 000 ha, respectively.

The predominance of sorghum cropping by mechanised cultivation methods is presenting severe problems. Virtual monocropping with sorghum causes rapid decline in soil fertility and serious infestation with sorghum-associated weeds, especially striga. The use of the disc harrow as the only tillage implement working the soil to the same shallow depth year after year is producing a hard soil layer. And delaying sowing until late July/early August (a consequence of relying on the secondary tillage operation to destroy germinated weeds, and hence save on the cost of weeding) on Vertisols is wasteful of available moisture, forces farmers to use low crop densities, and results in machinery being used under unfavourable conditions.

Ways to cope with these problems are suggested, such as adopting a crop rotation system in which sorghum occupies not more than half the land, and the area devoted to sesame is increased; making use of herbicides to permit early sowing; deep ploughing the land every 2-3 years, preferably with a chisel plough; and replacing the tall sorghum cultivars with dwarf types, which can be grown at higher densities and hence provide higher yields.


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