Sustainable phosphorus management option for non-flooded rice-lentil system in alkaline soil of Indo-Gangetic plain

Abstract

Aerobic rice cultivation has gained recognition for resource conservation and ecosystem services. However, aerobic/partially-aerobic rice productivity is often constrained by several deficiencies in soil-plant system including phosphorus (P), because of reduced soil P dissolution and crop P acquisition. The study aimed to design sustainable P management option(s) for non-flooded rice [system of rice intensification (SRI)]-lentil system in an alkaline Fluvisol by evaluating the effect of system-based sole fertilizer-P and integrated P management treatments on crop yields, soil P dynamics, P pools, soil biophysical and biochemical attributes. The treatments consisted of one control and three variable seasonal distribution sole fertilizer-P treatments [subscript value (kg P ha−1)] in non-flooded rice (SRI)-lentil (L) rotation ([SRI0-L0], [SRI22-L22], [SRI33-L11], [SRI11-L33]), three integrated P management treatments ([SRI11-L11+phosphate solubilizing bacteria (PSB)], SRI16.5-L5.5+rice residue incorporation (RR)+PSB, SRI5.5-L16.5+lentil residue incorporation (LR)+PSB)]. Besides this, a conventional flooded rice-lentil system with the recommended sole fertilizer-P rate ([PTR22-L22]) as a treatment was evaluated to compare soil P dynamics in flooded versus non-flooded rice ecologies. Soil P availability was significantly reduced (7–8%) in the non-flooded rice compared to the flooded rice ecology. The integrated treatment involving suboptimal fertilizer-P rate (22 kg P ha−1y−1), rice residue recycling, and PSB increased soil P availability in rice (5-6%) and lentil (9-10%) seasons as well as system productivity by 8.3% over the recommended sole fertilizer-P treatment ([SRI22-L22], 44 kg P ha−1y−1). The rice residue recycling integrated treatment increased NaHCO3-Pi (11%) and dissolved non-reactive P (6%) over the recommended sole fertilizer-P treatment. The positive effects of the lentil residue recycling integrated treatment on soil P availability and crop yields were relatively lower than the rice residue recycling integrated treatment possibly because of the lower residue C-input. Correlation results indicate that microbial biomass carbon, soil aggregation and labile organic carbon have a positive influence on P availability in this alkaline soil. The significant positive correlation between the active C-pool and total dissolved non-reactive P suggested that oxidisable C input could improve bioavailable P forms. Results indicated the role of balanced P fertilization in C-stabilization, which had the lowest in the P control treatment. The study with one soil type suggested that in-situ crop residue recycling integrated P management (rice residue in particular) could be a sustainable option for improving P bioavailability, nutrient cycling, and productivity of non-flooded rice-legume system in tropical alkaline soil, but, for the validation of the results, more studies with diverse soil properties are warranted.