SOIL NUTRIENT CHANGES WITH FERTILIZER TYPE IN CASSAVA-BASED CROPPING SYSTEM

The changes in soil nutrient status following the application of different fertilizer types were studied in field experiments involving maize-melon intercrop relayed into a cassava-soybean intercrop between 1995 and 1997. The soil at the experimental site was a Kanhaplic Haplustalf, which was under continuous cultivation with arable crops for seven years and fallow for four years. The effects of organic and inorganic fertilizers were investigated singly and in combination. The type of fertilizer had no significant effect on the soil pH, although, cropping significantly lowered the pH from 6.0 to 5.7. Cropping also significantly reduced the soil organic matter and total nitrogen (N). The soil organic matter (OM) and total N were most depleted with organic fertilizer application. Complementary application of organic and inorganic fertilizers limited the degree of depletion from 31.0 to 12.1 g kg−1 of OM and 1.8 to 0.6 g kg−1 total N. Soil available P was increased (60%) by inorganic fertilizer while the organic fertilizer increased it by 145% and the combined fertilizer by 186%. Exchangeable calcium (Ca) was depleted by about 12% with organic fertilizer application, 15% by inorganic fertilizer and about 19% with complementary application of organic and inorganic fertilizers. Exchangeable sodium (Na) was reduced from 0.43 to about 0.38 cmol kg−1 while magnesium (Mg) was increased from 0.5 to about 0.6 cmol kg−1.