Recycling of silicon-rich agro-wastes by their combined application with phosphate solubilizing microbe to solubilize the native soil phosphorus in a sub-tropical Alfisol.

It is imperative to find suitable strategies to utilize the native soil phosphorus (P), as natural rock phosphate deposits are at a verge of depletion. We explored two such cost-effective and eco-friendly strategies for native soil P solubilization: silicon (Si)-rich agro-wastes (as Si source) and phosphate solubilizing microorganism (PSM). An incubation study was conducted in a sub-tropical Alfisol for 90 days at 25 °C under field capacity moisture. A factorial completely randomized design with 3 factors, namely: Si sources (three levels: sugarcane bagasse ash, rice husk ash, and corn cob ash), PSM (two levels: without PSM, and with PSM); and Si doses [three levels: no Si (Si), 125 (Si) and 250 (Si) mg Si kg soil] was followed. The PSM increased solution P and soluble Si level by ∼22.2 and 1.88%, respectively, over no PSM; whereas, Si and Si increased solution P by ∼60.4 and 77.1%, as well as soluble Si by ∼41.5 and 55.5%, respectively, over Si. Also, interaction of PSM × Si doses was found significant (P<0.05). Activities of soil enzymes (dehydrogenase, acid phosphatase) and microbial biomass P also increased significantly both with PSM and Si application. Overall, PSM solubilized ∼4.18 mg kg of inorganic P and mineralized ∼5.92 mg kg of organic P; whereas, Si and Si solubilized ∼3.85 and 5.72 mg kg of inorganic P, and mineralized ∼4.15 and 5.37 mg kg of organic P, respectively. Path analysis revealed that inorganic P majorly contributed to total P solubilization; whereas, soluble and loosely bound, iron bound and aluminium bound P significantly influenced the inorganic P solubilization. Thus, utilization of such wastes as Si sources will not only complement the costly P fertilizers, but also address the waste disposal issue in a sustainable manner.