The Response of GRDB 15 to Increasing Levels of Slow-Release and Conventional Nitrogen Fertilizer Application

A field experiment was undertaken during the first crop of 2018 at the Rice Research Station located at Burma, Mahaicony latitude 6.49o and longitude -57.76o to look at the response of GRDB 15 to different sources and levels of nitrogen on growth, yield, nutrient uptake and soil chemical residue. The soil type was Litchfield clay having 197, 27 and 299 kg ha-1 of N, P and K with pH of 4.9 and soluble salts 270 ppm. The experiment was carried out in a randomized complete block design with three replications using variety GRDB 15. Treatments applied were 50, 75 and 100 kg N ha-1 in the form of urea and control release nitrogen fertilizer with 0 kg N ha-1as control. Results obtained showed that regular urea recorded higher growth, grain yield. Grain yield increased with increasing levels of nitrogen from both sources. For obtaining equivalent grain yield, 25 kg N ha-1 more of control release fertilizer needed to be added. Nitrogen uptake in both straw and grain increased with increasing levels of nitrogen for both sources of fertilizer. Control release nitrogen fertilizer had more residual soil nitrogen as compared to urea and it increased with increasing levels of nitrogen. At similar nitrogen levels, urea applications realized higher net returns as compared to control released nitrogen fertilizer. This is mainly due to higher grain yield for urea treatments and lower cost of fertilizer. The current GRDB recommendation for nitrogen application (75 to 100 kg N ha-1) in the form of urea still holds.