In areas with more than rains per year, the yields are more limited by the low supply of plant nutrients than by rainfall. Phosphorous is the most deficient element, but nitrogen deficiency also reduces yields. The nitrogen input does not produce any effect in case of phosphorus deficiency. Phosphorus is important at the beginning of the season particularly for root development. All crops can benefit from better soil fertility.  

Without fertilizer input in the 300 mm to 600 mm rainfall range, millet yield is only about 300 kg/ha. It is possible to harvest up to 2500 kg/ha of millet with a good management of soil fertility.

Long-term trials have shown the benefits of combining mineral fertilizer and organic fertilizer (Bationo and Buerkert 2001). At the same time it is important to reduce losses of plant nutrients through minimising soil erosion and leaching (Aune et al.1999). It is recommended to use all the organic fertilizer available and in addition to use a small amount of mineral fertiliser (microfertilisation). However, the quantity of organic fertilizers available per farmer is often very low because the organic fertilizer is used for other purposes. The use of mineral fertilizers may increase the amount of organic fertilizers available for increased yield.

Several methods can be combined in order to increase soil fertility. These methods are described below:

Organic fertilizer

Microdose

Cereals and cowpea intercropping

Mulching

Rock phosphate input

Regeneration of degraded lands

More information on soil fertility management:
http://www.fao.org/docrep/W7304F/w7304f0b.htm#TopOfPage

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