Effect of conservation agriculture and nutrient management options on soil phosphorus fractions under maize-wheat cropping system

With increasing adoption of conservation agriculture (CA), understanding of the impact of tillage, and residue retention and nutrient management options on the transformation of soil phosphorus (P) will give a brief idea of the extent of bioavailability of the different fractions, as low P availability in soil limits crop production. Thus, transformation and bioavailability of P through sequential fractionation was studied (0–5 and 5–15 cm) in maize-wheat cropping system with treatments consisting of four levels of tillage and residue regime (TR) as main plots i.e. conventional tillage (CT-RR); conventional tillage with residue incorporation (CT+RI+GI), maize and wheat on permanent beds with residue retention (PB+RR) and maize, wheat and green gram on permanent beds with residue retention (PB+RR+GR), and three nutrient management (NM) options in sub-plots i.e. farmer's fertilizer practice (FFP); recommended dose of fertilizers (RDF) and site-specific nutrient management (SSNM) in a split-plot design with three replications. Results showed that PB+RR+GR resulted in highest soil microbial biomass P (SMBP), Olsen-P, labile and moderately labile-P content amongst TR systems at 0–5 and 5–15 cm depths. The TR systems influenced the HCl-P but not the residual-P and total-P. Complete CA significantly increased total organic P (TPo) by 6.28% in the top 5 cm layer. Among the NM options, highest SMBP, Olsen P and labile P were registered under SSNM. The mean distribution of P fractions was: residual-P (32.1%) > HCl-P (27.8%) > NaOH-Po (22.2%) > NaHCO₃-Po (9.06%) > NaOH-Pi (6.28%) > NaHCO₃-Pi (1.39%) > water soluble P (WSP) (1.11%). The WSP was positively correlated with NaHCO₃-Pi, NaHCO₃-Po, NaOH-Po and TPo in both soil layers. Olsen P and SMBP were also positively correlated with labile P and NaOH-Po. The study showed that nutrient applied through SSNM approach rather than blanket recommendation enhanced the labile and available P in soil under CA.