Can the long-term impacts of zero tillage and residue retention increase soil legacy phosphorus availability under a maize–mustard system in an Inceptisol?

Context This study examines the legacy phosphorus (P) supply capacity of crops under a conservation agriculture (CA)-based maize (Zea mays L.)–mustard (Brassica juncea L.) system, particularly in Inceptisol soils of the hot semi-arid, sub-tropical north-western Indo-Gangetic Plains agro-ecoregion of India. Standard nutrient management protocols for CA remain a challenge due to the limited data on P dynamics in such systems. Aims To evaluate the effects of different tillage and residue management practices on soil legacy P availability and dynamics to improve nutrient management strategies in CA systems. Methods Soil samples were collected from a CA field experiment (2010–2011) at Pusa, New Delhi following a randomized block design after maize harvest from two depths (0–5 and 5–15 cm), with the following treatments: zero till maize (ZTMZ)−zero till mustard (ZTM), ZTMZ + Sesbania brown manuring (BM)–ZTM, ZTMZ with residue (+R)–ZTM(+R), ZTMZ(+R) + BM–ZTM(+R), ZTMZ–ZTM–zero till summer mungbean (ZTSMB), ZTMZ(+R)–ZTM(+R)–ZTSMB(+R), conventional till maize (CTMZ)–ZTM and CTMZ–conventional till mustard (CTM), with three replications. Various P fractions and adsorption parameters were analyzed using the Freundlich and Langmuir adsorption isotherms. Key results Compared to the conventional system (CTMZ–CTM), the ZTMZ(+R)–ZTM(+R)–ZTSMB(+R) treatment increased native soil available P by 81.3% at the 0–5 cm depth. Fractionation analysis showed that CA practices significantly enhanced water-soluble and NaHCO3-extractable P fractions. The highest P fraction was the HCl-P fraction, followed by the residual fraction. The CA treatments reduced P adsorption capacity, as indicated by lower adsorption affinity (a) and bonding energy (1/n) in the Freundlich isotherm, along with a decrease in maximum buffering capacity in the Langmuir isotherm. The ZTMZ(+R)–ZTM(+R)–ZTSMB(+R) facilitated greater P desorption, confirming its effectiveness in enhancing soil legacy P availability. Conclusions The results highlight the advantages of CA-based practices – particularly the ZTMZ(+R)–ZTM(+R)–ZTSMB(+R) – in improving soil P availability by boosting legacy P release and reducing P adsorption, ultimately leading to improved crop yields. Implications The study provides valuable insights for developing a sustainable and balanced nutrient management strategy under CA. The findings support the need for a precise and cost-effective P management protocol tailored to CA systems, ensuring long-term soil fertility and improved crop productivity.