Fermentative production of soluble phosphorus fertilizer using paddy straw: an alternate to biomass burning

Abstract

To mitigate environmental impacts caused by illegal burning of paddy straw or stubble in the open fields, an alternate and economical technology for microbial degradation of lignocellulosic biomass and production of soluble phosphorus fertilizer was explored. Low-grade Mussoorie rock phosphate and Udaipur rock phosphate supplemented paddy straw was exploited as solid-state fermentation medium for the fungal-mediated release of soluble phosphorus by phosphate dissolving and cellulase producing strains of Aspergillus niger (ITCC 6719) and Aspergillus awamori (F18). Optimization of process parameters revealed that elemental composition of rock phosphate and its dose are important to affect the per cent yield of soluble phosphorus. Addition of ammonium sulphate or ammonium nitrate or urea to rock phosphate supplemented paddy straw inhibited the release of soluble phosphorus. Contrarily, adding 10% wheat bran (w/w) into paddy straw-rock phosphate mixture and its subsequent fungal inoculation at 10% (v/w) resulted in maximum solubilization (37–38%) of rock phosphate on 21st day of incubation. The fermented extract of this mixture also recorded the highest cellulase activity titre (76.32 IU ml−1) after 3 weeks of fermentation. Soil–plant interaction studies with wheat crop revealed that application of this fermented mixture to soil not only improved the plant biomass but also increased the soil available phosphorus content by ~ twofold, compared to treatments receiving recommended chemical phosphorus. Bio-processing of rock phosphate using wheat bran-amended paddy straw as fermentation substrate can provide an economical and alternate soluble fertilizer for enhanced crop phosphorus nutrition.