Phosphorus Uptake and Balance in a Soyabean-Maize Rotation in the Moist Savanna of West Africa

Abstract

This study investigated the effect of maturity class on phosphorus (P) balance in a soyabean-maize rotation in the West African moist savanna.F our soyabean varieties of different maturity classes were grown with or without P fertilizer followed by a maize crop. Soyabean stover P content averaged 1.77 kg ha⁻¹ compared with 5.13 kg ha−1 in the grain. The late soyabean variety TGx1670-1F accumulated a significantly higher P in the grain (6.56 kg ha⁻¹), and stover (2.57 kg ha⁻¹) than the others. While P harvest index averaged 79%, P application increased grain P by 63-81% and stover P by 100% or more. When either soyabean grain or grain+stover was exported, P balance was negative and was not statistically different for varieties when no P was applied. At 30 or 60 kg P ha⁻¹, P balance was negative but significantly lower in TGx1670-1F compared with other varieties. In creasing P rate applied to soyabean significantly (p < 0.01) increased maize grain P by 35-66% in the second year. When P was exported only in soyabean grain, cumulative P balances after maize grain harvest (with no P or 30 kg ha⁻¹ applied previous year) were not significantly different for previous soyabean crops. At 60 kg ha⁻¹, however, P balance in previous TGx1670-1F plot was significantly lower than for other varieties. A further export of soyabean stover reduced P balance. Significant residual P effect was observed emphasizing the need to focus P fertilizer application in the cropping system rather than on the single crop. Also with more P in soyabean grain, a reduction in the extent of P depletion will be achieved by returning soyabean stover to the field after threshing.