Patcharee Saenjan, Wuttichai Juntarasombut, and Chana Saisompan

pp. 795 - 806

Abstract

In order to increase rice yields (RY) while reducing methane gas emissions (ME), several strategies
for methane mitigation were compared in a trial during the second rice growing season of 2003. A split plot
design was used, consisting of 2 water management (WM) treatments in main plots: 1) continuous flooding
and 2) intermittent drainage (by letting water evapotranspirate or drain away so as to maintain the soil
moisture content approximately at field capacity) during a part of the maximum tillering and flowering
stages; and five introgen (N) fertilizer treatments in sub plots: 1) no top-dressing of ferlilizers, 2) top-dressing of ammonium fulfate (AS, 21% N) at 15 kg per rai, 3) AS at 30 kg per rai, 4) urea (46%N) at 7 kg per rai
and 5) urea at 14 kg per rai. All plots received 16-16-8 at the rate of 20 kg per rai as a basal application.
Results indicate that WM had no significant effect on RY, but that intermittent flooding resulted in significantly less methane emission than continuous flooding. Top-dressing of N fertilizers had significant effect on both RY and ME. Top-dressing of urea at the rate of 14 kg per rai resulted in the highest RY, 912 kg per rai,
followed by top-dressing of AS at 30 kg per rai, which produced a yield of 874 kg per rai. Application of 30 kg
per rai of AS was more effective in decreasing in both total methane emission (TME) and methane emission
per unit grain yield (MPG) than the application of 14 kg per rai of urea. However, the highest benefit of 1,920
baht per rai and the highest income-cost ratio (I/C) of 2.11 were obtained by top-dressing of 14 kg per rai
of urea. The next best treatment was the application of AS at the rate of 30 kg per rai which resulted in a
benefit of 1,727 baht per rai, and I/C of 1.98. It was concluded that a basal application of 16-16-8 at the
rate of 20 kg per rai, followed by to-dressing with eith AS at 30 kg per rai or urea at 14 kg per rai (both
equivalent to approximately 6 kg N per rai) and intermittent drainage to maintain soil moisture at field
capacity could provide significantly higher RY, higher economic returns and lower methane emissions as
compared to continuous flooding and with no or litter N fertilization.