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.

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