Effect of Oxalic Acid on Increasing Soil Phosphorus Availability for Wheat

Most plants are able to increase soil phosphorus availability by exuding some compounds such as organic acids when they experience phosphorous deficiency. Considering this special ability of plants, the main purpose of the present research was to investigate if application of organic acids may increase P availability in soil. Therefore, a greenhouse experiment was conducted with five treatments of different combinations of mono-calcium phosphate and oxalic acid in a completely randomized design with three replications in a calcareous soil. Treatments were 68, 40.8, 27.2, 13.6, and 0 mg kg^-1 of phosphate fertilizer respectively combined with 1.6, 2.4, 3.2 and 4 mmol kg^-1 of oxalic acid in soil. Plants were harvested after two months. Then, shoot dry matter, P concentration and uptake of plant and soil P concentration were measured. The results showed that the range of oxalic acid concentration (1 to 4 mmol kg^-1 of soil) was effective for increasing phosphorus availability in soil. Applying oxalic acid instead of P fertilizer not only did not reduce plant dry matter, but also led to a significant increase in P uptake of plant. Moreover, phosphorous uptake efficiency of plant was increased by adding the oxalic acid to the soil. The results also showed that the combination of 27.2 mg kg^-1 of calcium phosphate (as 40 percent reduction in phosphorus fertilizer requirements of plants) and 2.4 mmol kg^-1 of oxalic acid was the best combination of acid and fertilizer among the other treatments for increasing the availability of phosphorus.