Exploitation of Orange Peel for Fungal Solubilization of Rock Phosphate by Solid State Fermentation

Present investigation focused on solubilization of Mussoorie rock phosphate (MRP) and Udaipur rock phosphate (URP) by fermentative production of organic acids from orange peel (Citrus sinensis) by Aspergillus awamori (F18). Adopting solid state fermentation (SSF) technology, fungus could be cultivated successfully on the autoclaved peel–rock phosphate mixture. To optimize the P release from the rock phosphates, the effect of process variables, such as bed load (2.5 and 5.0 g orange peel 100 ml−1 flask), the inoculum concentration (10, 20 and 40 %), the moisture content [57, 75 and 100 % of the maximum water retention capacity (MWRC) of the dried substrate] and incubation period (6–24 days) was investigated. Highest soluble P content of 1393.7 µg g−1 substrate was obtained on 24th days of incubation in bed load of 5.0 g substrate, supplemented with URP at humidification pattern of 75 % MWRC and 20 % inoculum (v/w). The recorded increase in soluble P content was 57 %, compared to its 2.5 g bed load counterpart. Oxalic, citric, succinic and malic acid were detected in fermented extract of both MRP and URP. However, their release was affected by the moisture content. Application of fermented orange peel–rock phosphate mixture in soil–plant system improved the available P and phosphatase activity of wheat grown soil by >45 %, compared to conventional practices. Production of soluble P fertilizer using orange peel in SSF is an economical and environment friendly technology that can find application in possible reduction of chemical P input in soil.