Improved fertilizer and water management practices for irrigated and rainfed lowland rice

Deep placement of urea supergranules (USG) gave the highest panicle number per unit area, dry matter, total N uptake, grain yield and N fertilizer and water use efficiencies regardless of water regime during the vegetative stress. Researchers' split of prilled urea (PU), with the initial dose broadcast and incorporated into mud, and sulfur-coated urea performed comparably well while farmers' split of PU performed the least. Addition of the nitrification inhibitor dicyandiamide to PU did not increase N uptake. In one experiment, researchers' split was found superior to farmers' split in all aspects of crop growth, except for N content where the latter performed better. Although, total N uptake at harvest was the same for the two N treatments, researchers' split produced significantly higher grain yields than did farmers' split regardless of water regime. With any N treatment, plots not irrigated for about 3-4 weeks during the vegetative stage gave yields equal to or higher than those of continuously flooded plots. This was due to higher N mineralization in stressed plots which consequently increased water use efficiency. Alternate wetting and drying cycles increased N losses due to sequential nitrification and denitrification. In another experiment, deep-placed USG was compared with researchers' split under varying degrees of moisture deficit. Deep placement of USG gave consistently higher yields than did researchers' split under all water regimes, especially under continuous flooding. Although high N uptake was noted in highly stressed (35 stress day) and in moderately stressed plots (21 and 28 days stress), severe water deficit prolonged crop maturity which coincided with low solar radiation during the reproductive stage, and thus may have substantially reduced yield. Results showed that use of improved fertilizer technology and proper water management practices may increase N fertilizer and water use efficiency. Mild moisture deficit at the vegetative stage was not detrimental to rice but harmful during the reproductive stage.