N-15-aided field experiments on evaluation of different methods of application of new slow-release nitrogen fertilizer for rice

A series of experiments with flooded rice were carried out at Fukuoka site to compare the efficiency of a single deep application of briquette urea (BU), a slow release fertilizer, with that of broadcasted and incorporated conventional urea fertilizer with 2 top dressings, to compare the response curve for BU and conventional urea application practice, and to observe the influence of different geometrical placement patterns of BU on growth and N-utilization by rice. 15N-labelled fertilizers were used in this study which supplements the INPUTS (Increasing Productivity Under Tight Supplies) Project. Broadcasted and incorporated urea with 2 top dressings was inferior to deep basal application of briquette urea in respect of N uptake and grain yield of rice in the paddy soil. 46 and 69 Kg N/ha from BU as basal deep placement were equivalent to 69 and 92 Kg N/ha, respectively, from urea fertilizer applied as split broadcasting in respect of grain yield. Geometric pattern of placement as 1 placement/2 hills was superior to lower or higher number of placements of BU in respect of grain yield and N absorption by rice in this soil. At the optimum rate of N applied (60 - 90 Kg N/ha) the observed recovery of fertilizer N was 59% when briquette urea was applied in placement pattern of 1 placement/2 hills. With increased number of placements, namely, 1 placement/1 hill and decreased number of placements, namely, 1 placement/4 hills, recoveries of fertilizer N of 47.4% and 46.8%, respectively, were obtained. In comparison, the recovery of fertilizer N from split application method of conventional urea was only 14%