Farmyard manure improves phosphorus use efficiency in weathered P deficient soil

Crop production is limited by low soil fertility in sub-Saharan Africa (SSA), particularly by P deficiency due to strong fixation by Fe and Al oxyhydroxides. Organic amendments are known to increase P availability in fertilizer and in such soils by different mechanisms. This study investigated the effect of adding farmyard manure (FYM) versus mineral triple super phosphate (TSP) fertilizer on P availability in different cropping systems. Field experiments were conducted in three succeeding summer seasons to compare two different upland cropping systems: a Bambara (Vigna subterranea)-rice rotation and a rice-rice system on a highly P deficient Ferralsol. Nine treatments including sole TSP at 0, 10, 20, 30 kg P ha(-1) year(-1), and sole FYM at 0, 10, 20, 30 kg P ha(-1) year(-1) (i.e. 100% FYM substitution), and combined FYM and TSP (FYM + TSP) at 20, 30 kg P ha(-1) year(-1) (i.e. 50% and 67% FYM substitution, respectively) were applied. Results showed that FYM treatments increased Bambara and rice grain yields compared to TSP treatment alone particularly in year three. Phosphorus uptake efficiency was higher in FYM treatments combined or not with TSP in year three of the experiment. The notable response to FYM was associated with increased agronomic efficiency resulting from additional C originating from the FYM with a low initial soil C content, (around 2%), and the effect of liming that reduced soil P sorption thereby improving P availability from FYM. Partial (67%) substitution of TSP by FYM increased grain yields of Bambara by 1.67 Mg ha(-1) and of rice by 1.01 Mg ha(-1) compared to TSP alone in year three at the highest P rate (30 kg P ha(-1)). The effect of FYM could be linked to inputs of C and nutrients from added FYM and to the indirect effect on soil physico-chemical properties including soil pH, soil moisture, soil biological activity, low P capacity sorption. This study confirms that application of FYM can help minimize rates of TSP applied in smallholder farms in SSA.