ORGANIC RESIDUE MANAGEMENT, SOIL NUTRIENT CHANGES AND MAIZE YIELD IN A HUMID ULTISOL

A study was conducted on an Oxic Paleudult in South Western Nigeria to evaluate the effects of organic residue treatments after clearing a 3 year secondary fallow land on soil nutrients, maize yield and profita bility. Burning of the fallow residue in 1993 and crop residue in situ in 1994 led to significant increases in soil pH, total N, organic mat ter, available P, exchangeable Ca, Mg and K within one month in both f ertilized and unfertilized treatments. However, the increases were not sustained till harvest and in most cases the concentrations of the nu trients decreased significantly below the pretreatment levels. Increas es due to residue incorporation were small but more sustainable, while in bare unfertilized plots the nutrients decreased below the pre trea tment levels throughout the period of the experiment. Maize yields wer e significantly higher in residue incorporated and burnt plots than in the bare plots with or without fertilizer application in both years. The influence of fertilizer application was profound. However, residue incorporation without fertilizer produced 84% of the yield obtained i n bare fertilized plots in 1993 and as much as 104% in 1994. The highe st profit was obtained when fertilizer application was combined with r esidue incorporation.