World’s Soil Resources

N P K
Country
1982-84 2000 1982-84 2000 1982-84 2000
(kg ha -1 yr -1 )
Benin
-1
4
-1
6
-1
-2 -9
-1
1
Botswana 0 -2 1 0 0 -2
Cameroon -20 -21 -2 -2
-1
2
-1
3
Ethiopia -41 -47 -6 -7 -26 -32
Ghana -30 -35 -3 -4
-1
7 -20
Kenya -42 -46 -3
-1
-29 -36
Malawi -68 -67
-1
0
-1
0 -44 -48
Mali -8
-1
1
-1
-2 -7
-1
0
Nigeria -34 -37 -4 -4 -24 -31
Rwanda -54 -60 -9
-1
1 -47 -61
Senegal
-1
2
-1
6 -2 -2
-1
0
-1
4
United Republic of Tanzania -27 -32 -4 -5
-1
8 -21
Zimbabwe -31 -27 -2 2 -22 -26
Table 9.3 Estimated nutrient balance in some SSA countries in 1982-84 and forecasts for 2000. Surce: Stoorvogel and Smaling, 1990;
Roy et al., 2003.
More nitrogen and potassium than phosphorus get depleted from African soils. Nitrogen and potassium
losses primarily arise from leaching and soil erosion. These soil problems result mainly from continuous
cropping of cereals without rotation with legumes, inappropriate soil conservation practices, and inadequate
amounts of fertilizer use. Among West African countries, Guinea Bissau and Nigeria experience the highest
annual losses of nitrogen and potassium. Nitrogen loss in East Africa is highest in Burundi, Ethiopia, Malawi,
Rwanda, and Uganda, and phosphorus loss is highest in Burundi, Malawi, and Rwanda (IFPRI, 1999).
Responses to nutrient decline
The negative nutrient balances clearly indicate that not enough nutrients are being applied in most areas
(Bationo et al., 2012). Annual application of nutrients in SSA averages about 10 kg of NPK per ha. Fertilizer tends
to be used mostly on cash and plantation crops because of the higher profitability of fertilizer application in
the production of cash crops. Food crops receive less fertilizer because of unfavourable crop/fertilizer price
ratios and financial constraints faced by farmers. In addition, food crops are only partly commercialized.
To maintain current average levels of crop production without depleting soil nutrients, Africa as a whole
(including North Africa) would require approximately 11.7 million metric tonnes of NPK each year, roughly
three times more than the continent currently uses (3.6 million metric tonnes) (Henao and Baanante, 1999).
Of this quantity, Sub-Saharan Africa would need by far the largest proportion (76 percent) because the current
average level of fertilizer use is so low. Total nutrient requirements per ha per year range from Botswana’s
24.5 kg ha -1 NPK (a figure 350 percent above current usage) to Reunion’s 437.3 kg ha -1 NPK (about 20 NPK per
ha less than the country consumes). Burkina Faso would have to increase its NPK consumption more than 11
times to maintain crop production levels without depleting nutrients and Swaziland would have to double
its consumption. Estimated average use for SSA as a whole would have to increase about 4 times to meet
nutrient needs at the current level of production. Generally, more nitrogen is required than potassium, and
more potassium than phosphorus.
Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes
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in Africa South of the Sahara