The potential of crop residue recycling for sustainable phosphorus management in non-flooded rice-lentil system in alkaline soil

Abstract Aerobic rice is gaining global recognition for its role in the conservation of water. However, its productivity is often constrained by several deficiencies in the soil-plant system. Particularly, in absence of flood-induced phosphorus (P) desorption, it is likely that P availability in aerobic soils would be reduced thus affecting the productivity. Presently, our understanding of soil P dynamics and its bioavailability in aerobic rice-based system(s) is limited, particularly in alkaline soils. In this study, the impact of sole fertilizer and integrated P management on soil P dynamics, biochemical and biophysical properties and crop yields in direct-seeded rice (DSR)-lentil rotation in alkaline soil was assessed to devise sustainable management option(s). Seven different P treatments in aerobic direct seeded rice-lentil system [subscript value (kg P ha−1)] i.e., P control (P[0−0]), three sole fertilizer-P treatments with variable rate application to component crops (P[22−22], P[33−11], P[11−33]), and three integrated treatments ([P11−11+ phosphate solubilizing bacteria (B)], [P16.5−5.5+ rice residue recycling (RR)+B], [P5.5−16.5+lentil residue recycling (LR)+B]) in aerobic direct seeded rice-lentil system along with a conventional flooded rice-lentil system with the recommended fertilizer-P rate (P[22−22]FR) were studied. Given the recommended sole fertilizer-P rate, the aerobic rice soil (P[22−22]) had lower available-P (8–10 %) compared to the flooded rice soil (P[22−22]FR). The rice residue recycling integrated treatment (P16.5−5.5+RR + B) increased soil available-P in both the rice (5–6 %) and lentil (12–13 %) crop season over the recommended sole fertilizer-P treatment (P[22−22]), and also increased the system productivity by 6–7 %. The higher NaHCO3-Pi (13 %) and dissolved non-reactive P (DNRP) (7%) in the treatment P16.5−5.5+RR + B over the treatment P[22−22] suggested a higher soil P mobilization potential of rice residue recycling integrated treatment. The effect of lentil residue recycling integrated treatment (P5.5−16.5+LR + B) and recommended sole fertilizer-P treatment P[22−22] was similar on soil P and crop yields, and would thus be an option when considering the reduction of P fertilizer use in aerobic rice. Soil aggregation, very-labile carbon, microbial biomass carbon, DNRP exhibited positive correlations with P bioavailability in the aerobic rice soil. Our results suggested that C-stabilization in aerobic rice soil is altered with P input, the lowest rate being recorded in the control treatment. Hence, the study concluded that reduced soil P availability could limit the productivity potential of aerobic rice-lentil system in alkaline soils, and integrated treatments involving in-situ crop residue recycling (rice in particular) and suboptimal fertilizer rate could improve soil P bioavailability, soil quality parameters, and crop yields, thus, recommended for sustainable management.