Burundi and Malawi also experienced rates of nutrient depletion above 100 kilograms of NPK per hectare per year. About 86 percent of African countries show annual nutrient deficits greater than 30 kilograms of NPK per hectare per year. More countries fall into the high depletion range than the medium range. Nutrient imbalances are highest where fertilizer use is particularly low and nutrient loss, mainly from soil erosion, is high. The low gains in nutrients, inherently low mineral stocks in these soils, and the harsh climate of the interior plains and plateaus aggravate the consequences of nutrient depletion.
Forfeited yields cause additional financial losses.
Most crop yields in Africa did not change substantially between 1981 and 1995, remaining close to the average obtained by smallholders with rainfed land and moderate to low soil fertility. 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. Guinea Bissau and Nigeria experience the highest annual losses of nitrogen and potassium in West Africa.