Rock Phosphate-enriched Pressmud Compost: Direct Effect in Pearl Millet (Pennisetum glaucum L.) and Residual Effect in Mustard (Brassica juncea) in a Typic Haplustept

Abstract

Rock phosphate-enriched pressmud compost (RPEPMC) was prepared by composting fresh pressmud and rock phosphate mixture in the ratio of 20:1 (w:w basis) in cylindrical plastic container with a composite microbial culture at 0.1% (w:w) level. A field experiment was conducted during rainy season (kharif) followed by winter (rabi) season of 2006-07 to evaluate the RPEPMC as partial substitute of fertilizer phosphorus (P) in terms of direct and residual P uptake and P use efficiency (PUE) by crops to study the changes in available P at 60 days after sowing (DAS) as well as after harvest of both the crops and various inorganic P fractions in soil after cropping. Results showed that pearl millet responded up to 26.1 kg ha-1 of P application. Application of diammonium phosphate (DAP) proved superior to RPEPMC with respect to grain and stover yield, P derived from P sources, total P uptake and PUE by pearl millet at 34.8 kg P ha-1 level. Among the various ratios of RPEPMC and DAP (3:1, 1:1 and 1:3) tried at 34.8 kg P ha-1 level, the 1:3 ratio showed best performance followed by 1:1 and 3:1 ratios. Phosphorus applied to pearl millet had considerable residual effect on succeeding mustard, the effect being more pronounced at higher levels of P application. The residual effect of P applied at 34.8 kg P ha-1 through RPEPMC and DAP produced 74.3 and 59.6% relative grain yield and 74.6 and 56.2% relative total P uptake, respectively at maturity against fresh application of 34.8 kg P ha-1 through DAP in mustard. The relative total P uptake by mustard at 34.8 kg P ha-1 through the three ratios was in the order of 3:1>1:1>1:3. Residual effect of RPEPMC and DAP in combination applied at 34.8 kg P ha-1 in a 3:1 ratio showed higher available P at 60 DAS as well as after harvest of mustard. Moreover, the application of RPEPMC in soils of medium available P status (Typic Haplustepts) in pearl millet-mustard sequence replaced about half to two-third of P requirement of crops from fertilizer with no appreciable change in soil P fertility.