Fertilizer efficiency of two types of coated urea in a pasture

In a 3-year experiment, we compared the fertilizer efficiency of sigmoidal releasing-type coated urea (CUS) and linear releasing-type coated urea (CUL) to that of readily available urea (RU). CUS and CUL were applied once in April, whereas RU was applied once in June and again in August. Nitrogen (N) release from CUS started from June to July and most of the N was released before August. The rate of N release in CUL plots was nearly constant between April and August. Herbage yield (HY) and N uptake between July and September increased stably in CUS plots in 2006 and 2008 and in CUL plots in 2008. HY and N uptake in RU plots increased at all sampling times after fertilizer application except in September in 2007. The HY and N uptake trend in 2007 differed to that in 2006 and 2008, due to unusually high temperature and low precipitation in the summer. The stability of seasonal herbage productivity was evaluated using F-tests for equality of variances of HY from May to September. Variances in CUS and CUL plots were not significantly different from those in RU plots. The annual and 3-year HY and N uptake in CUS and CUL plots were higher than those in RU plots. The annual mean N recovery rate was high in CUS (0.74–1.22) and CUL plots (0.84–1.27), as compared to that in RU plots (0.63–0.91). The 3-year mean recovery rate was estimated to be almost ‘1’ in CUS and CUL plots. This indicates that nearly all the N supplied by the fertilizer was taken up by herbage in the CUS and CUL plots. The superiority between CUS and CUL in terms of maximizing HY and N uptake was not clear; however, single application of CUS or CUL was more efficient for the herbage productivity than split application of RU.