Changes of phosphorus fractions in saline soil amended with municipal solid waste compost and mineral fertilizers in a mustard-pearl millet cropping system

Salinity affects phosphorus (P) fractionation and its availability in soil and thereby crop growth as well as yields. Therefore understanding of P transformation and availability in soil with use of different sources of P is crucial to adopt appropriate P management practices for improving productivity of saline soils. A field experiment comprising of four treatments replicated thrice was conducted for three consecutive years during 2012-15. Treatments consisted of control (Ct), recommended dose of N-P-K fertilizers at 60-30-30 kg ha(-1) (RDF-100%), municipal solid waste compost at 16 Mg ha(-1) (MSWC-16) and MSWC at 8 Mg ha(-1) + RDF-50% (MSWC-8 + RDF-50%) laid out in randomized complete block design. Among different phosphorous fractions across the years; saloid-P (S-P), iron-P (Fe-P), calcium-P (Ca-P) and occluded-P (Occ-P) increased markedly after 2012-13 with continuous increase in subsequent years in all treatments compared to Ct. However, MSWC-8 + RDF-50% produced significant increase in all P fractions, including Olsen-P, total-P (Pt) and inorganic-P (Pi), except S-P as compared to RDF-100%. Whereas, all P fractions progressively declined in Ct from 2012-13 to 2015, indicating continuous removal by mustard (Brassica juncea) and pearl millet (Pennisetumglaucum). MSWC-8 + RDF-50% also recorded 16 and 22% higher organic-P (Po) and alkaline phosphatase activity (ALPA), respectively during 2015 over 2012-13 in corresponding treatment. Soil organic carbon (SOC) increased with RDF-100% over Ct across the years as well as within year; however, the highest SOC (5.7 g kg(-1)) was observed with MSWC-8 + RDF-50%. Mean soil salinity (electrical conductivity; EC) decreased by 38 and 25% with MSWC-8 + RDF50% and MSWC-16, respectively relative to Ct (4.8 dSm(-1)). Relatively better P availability and lower soil EC with MSWC-8 + RDF-50% and resulted significantly higher mean (of three year) grain yield of mustard (2.38 Mg ha(-1)) and pearl millet (2.44 Mg ha(-1)) over RDF-100%. Nevertheless, RDF-100% produced 11 and 15% higher mean grain yield of mustard and pearl millet, respectively than Ct. MSWC-8 + RDF-50% also resulted in higher P uptake by grain of both crops as compared to RDF-100%. Our results highlighted that integrated use of organic amendment (MSWC-8) and mineral fertilizers (RDF-50%) is beneficial option for improving P availability and crop yields under saline conditions.