Phosphorus management strategies to increase lowland rice yields in sub-Saharan Africa: A review

Abstract

Phosphorus (P) deficiency is one of the major yield-limiting factors for lowland rice production in sub-Saharan Africa (SSA). Therefore, improved P management could be an effective strategy to increase lowland rice yields in SSA. The study reviews on historical and recent efforts for improving P management for lowland rice production in SSA together with their limitations and prospects for future research. Special focuses are on following three aspects: (1) suitable soil tests to assess the indigenous soil P supply and the yield response to P application in lowlands; (2) organic inputs and localized P application to the nursery bed (nursery P) and to the seedling roots at transplanting (P-dipping); (3) the interaction between P application and climate-induced stresses via its impact on phenological development. For the first aspect, we demonstrate the importance of considering the P adsorption and desorption kinetics in SSA soils, where large amounts of insoluble P complexes are bound to iron and aluminum oxides while these insoluble P pools are solubilized under submerged soil culture. We propose using the oxalate-extractable P, which extracts insoluble P pools bound to amorphous iron-oxide minerals, as a reliable test for measuring the indigenous soil P supply for lowland rice production. With respect to the second aspect, the efficient use of organic inputs—an important nutrient resource for smallholder farmers in SSA—can be reconsidered not only as a source of P but also as a substance to accelerate the chemical reaction and P solubilization in soils for lowland rice production. Several studies have demonstrated significant effects of nursery P and P-dipping to increase rice yields and agronomic P use efficiency (AE P ) as the yield gain per unit of P applied. Excess yield gains with a micro-dosing nursery P may have a risk of P mining from soils. The P-dipping retains the P input-output balance and achieves a consistently high AE P at 74–152 kg kg −1 . The third aspect has received little attention in the previous studies, although recent observations indicate that P management affects rice yields via its impact on phenological development. The time to heading under P deficiency can extend beyond three weeks, which allows plants to accumulate more biomass production while increasing the risk of biotic and abiotic stresses at the reproductive and ripening stages. Further attention should be paid to changes in phenological development and their interactions with climate-induced stress to develop improved P management practices in SSA. • Improved P management strategies can increase rice yield in sub-Saharan Africa. • Organic amendment increases effectively available P in soils and rice growth. • Localized P at nursery and transplanting stages increases rice yields with high AE P . • Improved P management should take into account the effect of P on rice phenology.