Organic materials with high P and low C:P ratio improve P availability for lowland rice in highly weathered soils: Pot and incubation experiments

Abstract

Background Phosphorus (P) deficiency remains a serious problem for lowland rice cultivation in Sub‐Saharan Africa. Locally available organic materials (OM) are potential amendment resources, but they vary widely in nutrient composition. How different OM affect P availability and rice production under different soil types remains poorly understood. Aims We aimed to determine soil responses to OM application varying in carbon (C) and P contents on P uptake, rice production, and P availability. Methods A pot experiment with eight different soils from lowland rice fields amended with four different farmer‐produced OM at an equal dose of 7.5 g kg–1 soil; and an incubation experiment with six soils amended with cellulose and two OM applied at the same C dose were conducted. Results An OM associated with high P and low C:P ratio increased shoot biomass and P uptake of rice in all soils by two‐ and threefold, respectively, compared to the control treatment. Low P saturation in soils (low P:Fe in oxalate extract) produced greater OM effects. Shoot biomass and P uptake decreased significantly in one soil with a high P saturation following application of the other three OM. Although increased soil P solubilization was observed with the addition of fresh C, OM effects on P availability were mostly attributed to their direct P supply. Conclusion OM with high P and low C:P ratio is effective in improving P availability for rice in P‐deficient lowland rice soils.