Influence of Temperature and Time on Nutrient Release Patterns of Osmocote Plusâ ¢, Nutricoteâ ¢, and Polyonâ ¢ Controlled-Release Fertilizers
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The objective of the second set of experiments was to determine the effects of temperature on short-term nutrient release. In Expt. 4, 14 g of each PCF was maintained at 40&176;C until ~33% of the NO3-N content in Osmocote Plusâ ¢ was expended. Each fertilizer was then placed in a sand column and leached with distilled water at ~100 mL/h. Columns were then incrementally subjected to a simulated diurnal container temperature change from 20&176;C to 40&176;C and back to 20&176;C over a period of 20 h. Leachate was collected hourly and measured for soluble salts and NO3-N and NH4-N concentrations. For all fertilizers, nutrient release increased and decreased with the respective increase and decrease in temperature. Nutrient release patterns of the three fertilizers were significantly different, with Osmocote Plusâ ¢ showing the greatest overall change in nutrient release between 20&176;C and 40&176;C and Nutricoteâ ¢ the least. In Expt. 5, PCFs were placed in flasks of distilled water in constant temperature baths. Initially, fertilizers were held at 40&176;C for three days and then at temperatures of 22, 28, 34, or 40&176;C for two weeks. Fertilizer solutions were poured off after the first and second weeks. Only solutions from the second week were analyzed for soluble salts and NO3-N, NH4-N, P, and K concentrations. For Osmocote Plusâ ¢ and Polyonâ ¢, there was a 29% to 86% (depending on the nutrient measured) mean increase in nutrient release between 22&176;C and 40&176;C, whereas for Nutricoteâ ¢ there was a 345% to 364% (depending on the nutrient measured) mean increase. The overall mean increases in nutrient release in Expt. 4 were between 1032% and 4023%, whereas the mean increases in Expt. 5 were between 29% and 364%. In summary, the second set of experiments found that PCF nutrient release was highly sensitive to diurnal temperature changes.
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