Phosphorus Release by Low Molecular Weight Organic Acids from Low-Grade Indian Rock Phosphate

Low molecular weight organic acids (LMWOAs) are naturally occurred in soil, particularly in the rhizosphere due to microbial metabolites and secretion of root exudates. Various functional groups present in LMWOAs can play an effective role in phosphorus dissolution. In this study, potentiality of LMWOAs for phosphorous release from low-grade Indian rock phosphates (RPs) collected from Udaipur, Jhabua and Purulia was investigated under laboratory conditions. The characteristic of P release and the factors influencing P release from selected low-grade RPs by using seven LMWOAs along with two inorganic acids were also investigated. The amount of P release from RPs with different acids at various concentrations and equilibrium pH as well as the different factors of P release was also compared. Results showed that the average amounts of P released by all the organic acids from the three RPs increased with the concentration of organic acids. The amount of P release by the organic acids from the RPs followed the order, i.e. oxalic acid>citric acid>tartaric acid>formic acid>malic acid>succinic acid>acetic acid. A negative correlation was observed between P released from RPs and an equilibrium solution pH. The average amounts P released from all sources of RP ranged from 12 to 81 mmol P kg(-1) by acetic acid and citric acid respectively. In addition, the nature of RPs, RP/acid solution ratio, leaching time and temperature significantly influenced the P release from RPs by organic acids. Thus, the LMWOAs could be a potential amendment for improving bio availability of P from RP.