Temperature dependence of nitrogen release rates from coated urea fertilizers having low temperature range

Abstract

Coated urea fertilizers, which can release nitrogen during various periods, are commonly employed in paddy rice cultivation because they enable topdressing omission. A mathematical model based on the Arrhenius equation that estimates the release over time was already established for paddy rice cultivation and was employed for estimating the amount of released nitrogen. The values of the parameters used in the model have been obtained for the temperature range (e.g. 15°C–35°C) that suits rice cultivation. In recent years, coated urea fertilizers have been employed in other crops but their suitability for this model in winter cropping at low temperatures has not been extensively studied. Therefore, when nitrogen releases of the 20 coated urea of polyolefin-based resin were investigated in the temperature range of 5°C–40°C, which is a wide temperature range including the low temperatures, it fitted the model well, and the parameters of the release rate precisely followed the Arrhenius equation. In addition, the activation energies of the parameters exhibiting the temperature dependence became almost constant for all brands. It would mean that the values of the activation energies became accurate by using data obtained in a wide temperature range including the low temperatures. Besides, two other parameters, release curve shape and release rate, also revealed a certain relationship with the release type of the coated urea fertilizer and the number of days required for 80% release in standard temperature (25°C) . This indicates that the model is also applicable to winter crops where temperatures are low. In addition, the regularity seen in the parameters suggests the validity of the model, and it is also expected that the estimation of the parameter values for the release estimation of various coated urea fertilizers become easy by using the regularity.