Residual Effects of Contrasting Organic Residues on Maize Growth and Phosphorus Accumulation over Four Cropping Cycles in Savanna Soils

Management options to improve phosphorus (P) availability in the West African savanna include the application of organic residues, separately or with inorganic fertilizers. The quality and quantity of organic resources affect their contribution to nutrient availability. The quality of residues influences decomposition and nutrient release in the short term but its importance in the long term is unclear. A greenhouse study with six different soils assessed the residual effect of contrasting organic residues (maize stover, farmyard manure, Senna siamea, Mucuna pruriens, Leucaena leucocephala, Gliricidia sepium, Pueraria phaseoloides, and Lablab purpureus) and triple superphosphate (TSP) on maize growth during four cropping cycles of 7 weeks. For the first cropping, the average shoot dry matter yield (DMY), 14 g pot–1 obtained with residues of carbon to phosphorus (C:P) ratio ≤200, was similar to the TSP treatment and higher than the yield obtained with maize stover (C:P ratio = 396). From the second cropping, the shoot DMY of the maize stover treatment (15 g pot–1) was higher than those of the other treatments. Both high- and low-quality residues had similar effects on the cumulative DMY. Cumulative shoot P accumulation in the maize stover treatment (53 mg pot–1) was significantly higher than in the control (30 mg pot–1) and similar to those from high-quality residue treatments. Significant interaction (P < 0.05) between soil and organic resource for DMY occurred only during the first two croppings. This indicates that the effects of soil type and residue quality on nutrient availability dwindle with time.