JWSS - Journal of Water and Soil Science

Organic acids play an important role in improving the bioavailability of soil nutrients. The objectives of this study were to determine the effect of oxalic acid on the release of soluble, exchangeable and non-exchangeable forms of K from micaceous minerals and potassium feldspars, and also to investigate the trend of K release by time. A laboratory study was carried out using a completely randomized design with two replicates. Biotite, phlogopite, muscovite, Zanjan and Yazd K-feldspars (< 50 &mu;m size) were treated with 0, 10 and 100 mM of oxalic acid solutions for a period of 5 hours and 20, 60 and 90 days. The amount of K was determined by flame photometer. The results indicated that most amount of soluble, exchangeable and no-exchangeable K was released by 100 mM of oxalic acid. The maximum soluble K (0.86 gKg-1) was released from phlogopite, and the maximum exchangeable and non-exchangeable K (1.5 and 29.6 gKg-1, respectively) were released from biotite. Muscovite with 0.19, 0.34 and 1.41 gKg-1 of soluble, exchangeable and non-exchangeable K, respectively, had the lowest release of K among the studied minerals. The kinetics K release from minerals consisted of two phases. The first phase was relatively rapid and then it had a slow rate until the end of the experiment. Given that the applied concentration of organic acid was high, potassium release during the experiment period did not reach the steady state. Therefore, a longer period of release experiment is suggested.