ABSTRACT
Phosphorus deficiency is a major constraint that limits food production in Nigeria, especially under acidic soil conditions. Presently, successful production of high nutrient requiring crops such as maize is only possible with the use of inorganic phosphate fertilizers which are very costly and often unavailable to the farmer. In an attempt to address this problem, field trials were conducted on two fields located at Samaru (11011'N,7038,E) and one field at Heipang (9Â38'N, 8Â53'E) to evaluate the response of various cover crops and maize to native and applied phosphate, and to evaluate the effects of these treatments on the performance and P nutrition of succeeding maize in rotation. The two locations selected for the trials had widely contrasting soil phosphate properties. Samaru soil, classified as Kanhaplic Haplustalf following the USDA soil taxonomy system, had low P sorption capacity with pH values of 5.5, available soil P concentration of between 6.04 to 9.86 and total P content of between 154 to 196 mg Kg"1. Heipang soil on the other hand, was classified as Typic plinthustult and had very high P fixing capacity with pH value of 5.4, available soil P concentration of 0.69, and total P content of 473 mg Kg"1. Results of the study at Samaru showed that among the cover crops evaluated, Crotalaria ochroleuca was the most P efficient in terms of total amount of above ground biomass per unit P taken up, while Phaseolus vulgaris (brown) and Clitoria ternatea were the least efficient. The yield of maize preceded by Lablab purpureus (white), Lablab v i purpureus (black), Chamaechsta rotundifolia, and Mucuna pruriens was increased by over 50% at Samaru in the first year after cover cropping. The positive effects of these cover crops on yield of succeeding maize did not manifest in the second. On Heipang soil, with high P sorption capacity, only Chamaecrista rotundifolia produced some significant improvement in the performance of succeeding maize in terms of height and stover yield. However, Chamaecrista rotundifolia, Zeamay intercropped with Chamaecrista rotundifolia, Mucuna pruriens (white), and Lablab purpureus (white) reduced the leaf Al concentration of succeeding maize by more than 38% at Heipang. Effects of Sokoto phosphate rock on maize yields and available soil P at Samaru started manifesting only in the third year of cropping when the soil P was sufficiently depleted (< 5.0 mg Kg"1) to force the dissolution of phosphate rock. At Heipang, on the other hand, where the available soil P was extremely low (< 1 mg Kg"1), the effect of Sokoto phosphate rock on maize yield manifested in both years of cropping. Optimum yield of maize at Samaru was obtained with the application of 30 Kg P ha*1 in form of single superphosphate., while at Heipang even the application of 60 Kg P ha'1 did not produce optimum yield. Application of 1.35 t CaO ha"1 to Heipang soil in 1997 significantly raised the soil pH value by about 0.2 and improved the total P uptake of maize grains but did not improve available soil P and grain yield.
