Conservation agriculture increases phosphorus pools and stock in the top 30 cm of soil: A three‐year study on a subtropical legume–rice rotation

Abstract The adoption of conservation agriculture (CA) practices is likely to alter soil phosphorus (P) pools and availability leading to changes in P fertilizer use and management. However, the impacts of CA practices on soil P fractions and their distribution in the soil profile under rice‐based systems is not well‐understood. This study examined the effect of two crop establishment practices (strip planting, SP and conventional tillage, CT) and two crop residue levels (high residue, HR‐ 40% of above ground biomass and low residue, LR‐ 15%) on P fractions in the soil profile under a lentil–mungbean–rice sequence. After three consecutive years of CA practice, covering nine crops, composite soil samples were collected at 0–5, 5–15, 15–30, 30–45 and 45–60 cm depths and analysed for solution P, NaHCO 3 ‐extracted inorganic (NaHCO 3 Pi) and organic (NaHCO 3 Po) P, NaOH‐extracted inorganic (NaOH Pi) and organic (NaOH Po) P, stable P, residue P, total P, soil organic carbon (SOC) and total nitrogen (N). The inorganic P (solution P, NaHCO 3 Pi, NaOH Pi and stable P) comprised 53–59% while the organic P (NaHCO 3 Po and NaOH Po) comprised only 6%–13% of total P. However, CA practices increased SOC with the corresponding increase in soil organic P fractions. HR increased solution P, NaOH Po, stable P, residue P, total P, as well as SOC contents along with the stocks of total carbon (C), N, and P at up to 15 cm while increasing NaHCO 3 Pi, NaOH Pi and TN at up to 30 cm depth compared with the LR. Likewise, SP increased the inorganic P fractions (NaHCO 3 Pi and NaOH Pi) at 0–30 cm depth over the CT while P fractions in the deeper soil layers were similar to each other. In conclusion, the increase in soil P pools at up to 15–30 cm depths especially because of increased crop residue retention should allow for a decrease in P fertilizer inputs in intensive rice‐based systems.