Micronutrient Availability as Affected by the Long-Term Application of Phosphorus Fertilizer and Organic Amendments

Micronutrient availability is important to crop production and can be affected by long-term application of P and organic amendments. This study was conducted to determine the effects of the long-term application of different sources and rates of P application on extractable [DTPA-sorbitol (diethylenetriamine-pentaacetic acid and sorbitol] micronutrients. Soil extractable and total micronutrients (B, Cu, Fe, Mn, Mo, and Zn), pH, and organic matter content were determined from sites across Oklahoma that had received long-term applications of beef manure, swine effluent, biosolids, or commercial fertilizer. Three continuous inorganic P experiments that had been conducted for 36 to 39 yr and three organic P experiments that had been conducted for 11 to 12 yr were evaluated. The long-term application of inorganic P had little effect on micronutrient availability. However, long-term application of biosolids significantly (p < 0.05) increased extractable Cu, Fe, Mo, and Zn in soil, while long-term application of beef manure significantly increased all the micronutrients evaluated. Similarly, the long-term application of swine effluent significantly increased extractable B, Cu, Mo, and Zn in soil. The addition of micronutrients from organic amendments increased micronutrient availability, while long-term inorganic P application had little effect. The result of our study indicates organic amendments make an ideal fertilizer source for areas with micronutrient deficiencies.