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Field trials on controlled release fertilizers (CRF) and a nitrification inhibitor (NI) were conducted in order to show their potential to increase N use efficiency (NUE) and to conserve air and water quality. For this purpose, flood irrigated barley grown on a clay soil (Colorado, USA), center-pivot irrigated potato grown in a sandy field (Colorado, USA), and corn grown on a loamy soil at a large scale lysimeter (Fukushima, Japan) were selected. NI (dicyandiamide) and CRF (polyolefin coated urea) were capable of reducing N2O emissions from urea applied to the barley field by 81 % and 35 %, respectively. Total N fertilizer losses averaged 15 and 10 % in the NI and urea treatments, respectively. On the other hand, those from the CRF treatment averaged only 1.9 %, indicating that CRF showed the highest potential to increase N use efficiency. The trials in the potato field demonstrated that CRF could markedly increase NUE and tuber yields. A single basal application of CRF at planting (N rate, 112 kg ha−1) produced tuber yields comparable with those of traditional fertilizer applications (112 kg N ha−1)by basal dressing, 90 kg N ha−1 by topdressing and 67 kg N ha−1 by 8 fertilizations). The urea and CRF plots in the corn fields showed similar N2O emission patterns, having two high emission periods following the basal and topdressed N applications in the urea plots and the enhanced N release from a short linear formulation and a long sigmoidal formulation in the CRF plots, respectively. However, the total N2O emission value of the CRF plots was almost one third of that of the urea plots. The plant recovery of CRF N was almost two times of that of urea N. Finally, the authors discussed that contributions of CRF and NI to conserve air and water quality are basically due to maximizing NUE and reducing the N fertilization rate.
Shoji et al. (Mon,) studied this question.