LONG-TERM EFFECT OF CASSAVA CULTIVATION ON SOIL PRODUCTIVITY

Cassava (Manihot esculenta Crantz) is usually grown by poor farmers in the tropics with a minimum of inputs. Continuous production under these conditions can lead to soil nutrient depletion. On sloping land, cassava cultivation can also cause severe erosion if the crop is not properly managed. This paper reviews the literature to show that cassava does extract large amounts of nutrients, especially potassium (K), from the soil. However, when nutrient extraction is calculated on the basis of per unit quantity dry-matter produced, cassava extracts much less N and P than, and similar amounts of K to, most other crops. Long-term fertility trials indicate that, without adequate K fertilization, cassava yields eventually decline due to K depletion, except in those soils containing large amounts of K-bearing minerals. While cassava production may result in severe erosion when grown on steep slopes, simple agronomic practices can usually maintain soil losses within acceptable levels. The effect of different cultivation practices on erosion and yield varies from location to location, and the most appropriate practices can be identified through simple erosion-control trials on farmers' fields. Thus, productivity of continuously grown cassava fields can be maintained through judicious use of fertilizers and soil management practices that control erosion.