EFFECT OF SEEDING RATE AND NITROGEN MANAGEMENT UNDER TWO DIFFERENT WATER REGIMES ON GRAIN YIELD, WATER PRODUCTIVITY AND PROFITABILITY OF RICE PRODUCTION

The objective of this study is to quantify the impact of new irrigation method (alternate wetting and drying: AWD) on grain yield, water productivity and economic efficiency under different seeding rates and nitrogen application methods in comparison with the conventional water management, continuous flooding (CF). The experiment was laid out in 2006 wet season and 2007 dry season at CLRRI, following a randomized completed block design with four replications and six treatments in combination of three seeding rates and methods (row seeding at 70 kg ha -1 (P1), broadcast at 70 kg ha -1 (P2) and broadcast at 120 kg ha -1 (P3) and two nitrogen management methods [Current SSNM recommendation (N1) and Alternative nitrogen management (N2)]. The two water regimes were physically separated in the plots to ensure that seepage of water did not interfere together. Grain yields were varied from 2.68 to 2.76 tons ha -1 in 2006 wet season (WS) and from 5.81 to 5.98 tons ha -1 in 2007 dry season (DS) at AWD, while higher grain yields attained at CF. It got the grain yields from 2.75 to 2.90 tons ha -1 and from 6.03 to 6.10 tons ha -1 , respectively. The differences in grain yield were statistically significant only in 2007 DS. Although the higher grain yields of CF, the AWD reduced the irrigation water inputs compared to those. It reduced 33.3% of irrigation water input in 2006 WS and 28.6% in 2007 DS. Water productivity of AWD was also increased compared to CF. It got 1.4 kg m -3 and 0.9 kg m -3 in 06 WS and 1.6 kg m -3 and 1.2 kg m -3 in 07 DS, respectively. The net benefit of AWD water use attained higher value than CF of 154 thousand VND ha -1 in 06 WS and 1.02 million VND ha -1 in 07 DS. The difference of profit between two seeding rates 70 and 120 kg ha -1 was 208 thousand VND ha -1 in 06 WS and 285 thousand VND ha -1 in 07 DS. The difference of net benefit between two nitrogen management methods was 118 thousand VND ha -1 and 248 thousand VND ha -1 in 06 WS and 07 DS, respectively.