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Title: Macro- and micro-nutrient release characteristics of three polymer-coated fertilizers: Theory and measurements

Author
item ADAMS, CURTIS - Utah State University
item Frantz, Jonathan
item BUGBEE, BRUCE - Utah State University

Submitted to: Journal of Plant Nutrition and Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2013
Publication Date: 3/1/2013
Citation: Adams, C., Frantz, J., Bugbee, B. 2013. Macro- and micro-nutrient release characteristics of three polymer-coated fertilizers: Theory and measurements. Journal of Plant Nutrition and Soil Science. 176(1):76-88.

Interpretive Summary: n spite of much research, there persists a poor understanding of how fertilizer is released from slow-release fertilizers, also known as polymer-coated fertilizers (PCF). In this report, we extend current conceptual models that describe release mechanisms and expand upon them by describing the critical effects of moisture and temperature on release of all essential nutrients of three commercially available PCF types: Polyon®, Nutricote®, and Osmocote®, each with two time-frame release formulations. We quantified nutrient release at weekly intervals for nearly a year in a range of temperatures from 5 to 40ºC. We did these both in water and chemically inert sand, which allowed for quantification without complicating effects from chemically active soils or soilless media. Contrary to several published reports, our results indicate that there is no significant difference in nutrient release rates in water and a moist, solid, inert substrate. This means that release rates determined in water, a much simpler system to manage, can be used to model nutrient concentrations in more chemically and physically complex substrates if the soils are characterized for their own, separate properties. Across all PCF, temperature most influenced nitrogen, potassium, boron, copper, and zinc, while the least affected were phosphorus, magnesium, and iron. We also found differences among the coating technologies or brands. Osmocote fertilizers released faster than specified at both high and low temperatures. Nutricote had relatively steady release rates over time and a nonlinear response to temperature. Polyon released more slowly than specified but were highly uniform. Together, these data allow for improved predictions of fertilizer availability in different substrates, and allow users to anticipate when leaching events may release specific nutrients and when plants may require further fertilizer management.

Technical Abstract: In spite of several published studies we have an incomplete understanding of the ion release mechanisms and characteristics of primary polymer-coated fertilizer (PCF) technologies. Here we extend current conceptual models describing release mechanisms and describe the critical effects of substrate moisture and temperature on macro- and micro-nutrient release of three PCF types: Polyon®, Nutricote®, and Osmocote®. Nutrient release was quantified at weekly intervals for up to 300 days from 5 to 40ºC in water and chemically inert sand, substrates that allowed release quantification without confounding effects of ion sorption/desorption. At least two release timeframe formulations of each PCF type were studied and all products had similar nutrient concentrations to allow isolation of the effect of coating technology. Contrary to several studies, our data and model indicate that there is no significant difference in nutrient release rates in water and a moist, solid substrate. This means that release rates determined in water can be used to model bio-available nutrient concentrations in moist soil or soilless media where sorption/desorption properties alter concentrations after release. Across all PCF, the nutrients most affected by temperature were typically N, K, B, Cu and Zn, while the least affected were P, Mg and Fe. We also found consistent differences among the coating technologies. Osmocote fertilizers released faster than specified at both high and low temperatures. Nutricote had relatively steady release rates over time and a nonlinear response to temperature. Polyon released more slowly than specified but replicate samples were highly uniform.