Fertility and productivity index rating of some soils conditioned by climate and topography

In the humid tropics, well-drained soils with abundant loose iron concretions, soils with very little weatherable minerals left and of poor chemical status due to the abundance of low activity clays, pose serious limitations to agricultural productivity. Accurate and reliable soil productivity information is needed in the form of crop yield estimates and productivity indices. We investigated the productive potential of some acrisols and plinthosols by computing productivity indices (PI) and estimating yields of four test crops, namely cowpea, groundnut, maize and soybean. PI was based on physico-chemical parameters expected to regulate air-water relations, have a role in determining the mechanical resistance to crop roots and the volume of soil, and, contribute to the fertility status of the soils. Very low Pls in the order 7.2x10-5, 9.6x10-5 and 8.32x10-4 were observed for Nyankpala, Changnayili and Kpelesawgu series respectively. Based on the inherently low fertility status of these soils, maize, planted as a sole crop or in rotation with groundnut is the sustainable cropping system for the soils. A return of crop residue to the soil is envisaged as a long term practice to maintain adequate levels of organic matter. (author)