Manipulation of Localised Nutrient Placement to Enhance Synergistic Effects of Nitrogen and Phosphorus for Rice 

Abstract Background: Point application of fertiliser containing only immobile phosphorus (P) at a site distant from crop roots may limit plant P capture and grain yield. We investigated whether a localised application of P together with nitrogen (N) could offset this limitation in rice (Oryza sativa L.). We postulated that N in this combined fertiliser would stimulate root proliferation, thereby promoting uptake of P. Results: We conducted a pot experiment using three localised nutrient supply treatments (N-only, P-only, and combined N and P) applied at sites near (3 cm) and distant (10 cm) from rice seedlings. We also tested the effects of homogeneous NP supply. Grain yields were similar between the homogeneous NP supply and localised N-only supply, regardless of placement distance. P-only supply with 10 cm placement reduced grain yield by 30%. Root length density was considerably greater around the placement site in the localised N-only treatment compared to the P-only at both placement distances. Hence, localised combined N and P supply offset reductions in yield and nutrient uptake realised under the P-only supply with 10 cm placement. Root mass density and root/shoot dry weight ratio were greater under the localised N-only supply than in the NP combination with 3 cm placement. Hence, localised combined N and P supply with 3 cm placement enhanced grain yield (by 33%) than the N-only supply. Conclusion: The synergistic effects of localised fertilisation with N and P can be maximised through precise manipulation of specific placement distances for favourable root architecture and high crop yield.