Role of phosphate-solubilizing microbes in the enhancement of fertilizer value of rock phosphate through composting technology

Abstract

Preparation and use of enriched compost has become an important component of sustainable agriculture and received much interest in recent years as a means of alternative utilization of crop residues and low-grade minerals like rock phosphate (RP) by composting technology, thus reducing the ill effects of residue burning as well as improving the P content. The process has many advantages including sanitation, mass and bulk reduction, and decrease in carbon-to-nitrogen (C/N) ratio of crop residues. The performance of compost depends on the quality of the substrate. However, composts prepared from farm wastes have low nutrient content, particularly phosphorus (P) and potassium (K), and are considered poor suppliers of nutrients to crops. A possible means of improving the nutrient content, after prepare enriched compost by addition of low-grade RP and microbial techniques for RP solubilization. It will not only help farmers in supplying plant nutrients at a very low investment but also keep the environment pollution-free. The mineralization of insoluble forms of P present in RP by organic acids released during decomposition of organic matter is the major advantage of preparation of enriched compost. Organic acids released from the various organic materials used in the composting help in breaking down the RP faster during the composting period by pushing the dissolution reaction to the forward direction. The availability of P also increases due to inoculation with PSM, which are also known to produce organic acids. These acids are able to dissolve the mineral phosphate and make it available for the plant. The composting of organic wastes with RP has been demonstrated to be an effective method for producing end-products which are ensuring their maximum benefit foragriculture. Here, we emphasize pre-application techniques, especially the cocomposting of RP with various organic by-product materials that include crop residues. A range of laboratory incubations have demonstrated the underlying mechanisms involved with solubilization. The significance of microbial induced production of organic acids and acidity during composting is particularly important in this respect. Inoculation with Aspergillus awamori into the composting mass increased the content of total P (2.35%) as well as water-soluble P (0.05% P) and citrate-soluble P (0.85% P) significantly. While co-composting with RP offers a great potential that could be developed for use at the individual farm scale, the key controlling factors and underlying mechanisms are far from being fully understood. Studies on synchronization of nutrient mineralization and crop demand will provide information on the efficient use of RP-enriched compost in a more integrated manner with inorganic fertilizers for achieving sustainable higher crop productivity.