Residual effects of phosphorus and soyabean crop on maize in the Guinea savanna of West Africa.

摘要

Two seasons of cropping were carried out at three sites in the Guinea savanna to evaluate the residual effects of soyabean on maize. The experiment was laid out as a split-plot design in a randomized complete block with three replications. In the first season, four soyabean varieties with a fallow treatment (control) received phosphorus (P) applied as triple superphosphate (20% P) at the rates of 30 and 60 kg P ha-1. Maize was grown in these plots in the second season without fertilizer application. At all sites, regardless of the previous crop, total soil N remained low (<1.5 g kg-1). Available P was affected by the P rate in the previous year at all sites. From initial values ranging from 5.2-16.2 mg kg-1 in the first season, available P significantly (p<0.05) increased in the second season to 9.8-42.8 mg kg-1 when 30 or 60 kg P ha-1 was applied, compared to 7.7-18.6 mg kg-1 at no P application. Relative to no P application in the previous year, the application of 60 kg P ha-1 significantly increased total dry matter at 6 weeks after planting by 19%, total harvest dry matter by 28%, and grain yield by 37%.