Genotypic Variation in Grain P Loading across Diverse Rice Growing Environments and Implications for Field P Balances

Elke Vandamme, Matthias Wissuwa, Terry Rose, Ibnou Dieng, Khady N. Drame, Mamadou Fofana, Kalimuthu Senthilkumar, Ramaiah Venuprasad, Demba Jallow, Zacharie Segda, Lalith Suriyagoda, Dinarathna Sirisena, Yoichiro Kato, Kazuki Saito

More than 60% of phosphorus (P) taken up by rice (Oryza spp.) is accumulated in the grains at harvest and hence exported from fields, leading to a continuous removal of P. If P removed from fields is not replaced by P inputs then soil P stocks decline, with consequences for subsequent crops. Breeding rice genotypes with a low concentration of P in the grains could be a strategy to reduce maintenance fertilizer needs and slow soil P depletion in low input systems. This study aimed to assess variation in grain P concentrations among rice genotypes across diverse environments and evaluate the implications for field P balances at various grain yield levels. Multi-location screening experiments were conducted at different sites across Africa and Asia and yield components and grain P concentrations were determined at harvest. Genotypic variation in grain P concentration was evaluated while considering differences in P supply and grain yield using cluster analysis to group environments and boundary line analysis to determine minimum grain P concentrations at various yield levels. Average grain P concentrations across genotypes varied almost 3-fold among environments, from 1.4 to 3.9 mg g(-1). Minimum grain P concentrations associated with grain yields of 150, 300, and 500 g m(-2) varied between 1.2 and 1.7, 1.3 and 1.8, and 1.7 and 2.2 mg g(-1) among genotypes respectively. Two genotypes, Santhi Sufaid and DJ123, were identified as potential donors for breeding for low grain P concentration. Improvements in P balances that could be achieved by exploiting this genotypic variation are in the range of less than 0.10 g P m(-2) (1 kg P ha(-1)) in low yielding systems, and 0.15-0.50 g P m(-2) (1.5-5.0 kg P ha(-1)) in higher yielding systems. Improved crop management and alternative breeding approaches may be required to achieve larger reductions in grain P concentrations in rice.