SUBSOIL PRODUCTIVITY OF AN ULTISOL IN NIGERIA AS AFFECTED BY ORGANIC WASTES AND INORGANIC FERTILIZER AMENDMENTS

Abstract

In a greenhouse study using maize as the indicator crop, I assessed the comparative effectiveness of various organic wastes and inorganic fertilizers on improving the subsoil productivity of an Ultisol in southeastern Nigeria. The organic wastes used, at the rates of 0 and 5%, were poultry manure, rice husk, sawdust, and compost manure. The fertilizer treatments were none and complete NPKMg applied at the rates of 60 ppm N, 15 ppm P, 60 ppm K, and 20 ppm Mg. The yields on subsoil were compared with those on the unamended topsoil, as well as those on the corresponding topsoil treatments. Without any amendments the topsoil outyielded the subsoil by 21%. Application of complete fertilizer also resulted in 29% higher yield on the topsoil than the subsoil. Organic wastes application produced higher yield responses on the subsoil than on the topsoil. Poultry manure addition resulted in the highest dry matter yields on the subsoils, outperforming compost manure by 60%, rice husk + NPKMg by 72%, rice husk alone by 78%, sawdust + NPKMg by 90%, and sawdust alone by 93%. With the exception of sawdust all the other amendments proved better than complete N, P, K, and Mg at the rates used. This is a reflection of the amount of nutrients supplied by the respective materials. Nutrient uptake also reflected the nutrient content of the organic wastes. The uptake of N and P varied inversely as the C:N and C:P ratios of the organic wastes. Higher doses of inorganic fertilizers than the rates used may be required to achieve yields comparable to those obtained on subsoils amended with either poultry manure, compost manure, or rice husk. © Williams & Wilkins 1985. All Rights Reserved.