Fertilizer–use efficiency of amended urea materials in flooded rice

summary In a field experiment on a typic hapludoll in 1983 and 1984, deep placement of urea supergranules at 40 and 80 kg N/ha proved to be the best N source, of five tested, for grain production, but at 120 kg N/ha it was similar to neem-cake-coated urea. The results showed that deep placement of urea supergranules can save fertilizer use by 60% compared with prilled urea to obtain the same yield. Shellac-coated urea and dicyandiamide-coated urea was more effective than prilled urea in 1984. Differences in dry-matter production and grain yield were directly related to N uptake by the plants. On average, apparent recovery of applied N increased from 35% for prilled urea to 55, 52·5,46·5 and 37·5% for urea supergranules, neem-cake-coated urea, shellac-coated urea and dicyandiamide-coated urea, respectively.