Excessive application of N fertilizer to rice results in water and atmospheric pollution including greenhouse gas (GHG) emissions. Therefore, N fertilizer management needs to be optimized taking into account grain yield, global warming potential (GWP, Mg CO2 eq. ha(-1)) and GHG intensity (GHGI, kg CO2 eq. kg(-1) grain). However, the tradeoffs between the effects of N rate on rice grain yield, GWP and GHGI have not been adequately evaluated. Therefore, field experiments to determine the effect of N rate (as urea) on yield, GWP and GHGI were conducted in a typical flooded, transplanted rice paddy in a temperate environment. Methane (CH4) and nitrous oxide (N2O) emission rates were determined throughout the entire year (both during growing and fallow seasons) over two years. Rice grain yield showed a quadratic response to N rate, and the maximum yield (6.7-6.8 t ha(-1)) was achieved at 112-119 kg N ha(-1), 50% higher than the yield of the control (0 kg N ha(-1)). Increasing N rate increased the seasonal N2O flux by 4.56-7.11 g N2O kg(-1) N, but N2O flux contributed less than 7% of the total GWP. The GWP was mainly determined by the CH4 flux, which showed a relatively flat quadratic response to N rate, peaking at 124-138 kg N ha(-1). Thus, GWP also showed a quadratic response to N rate, peaking at 122-130 kg N ha(-1). The GHGI decreased as N rate increased and was the lowest (1.10-1.28 kg CO2-eq. kg(-1 )grain yield) at 104-112 kg N ha(-1), approximately 20% lower than GHGI in the 0 N treatment. In conclusion, the N rate for maximum yield was similar to the N rate for minimum GHGI, mainly because of the small effect of N rate on CH4 emissions and the low magnitude of N2O emissions. Thus, GHGI was largely driven by grain yield, so the N rate for maximum grain yield was similar to the N rate for maximum GHGI. Proper N fertilization is essential in rice farming systems to increase crop productivity and reduce the global warming impact (GWP and GHGI).
1.Western Sydney Univ, Hwakesbury Inst Environm, Penrith, NSW 2751, Australia 2.Gyeongsang Natl Univ, Inst Agr & Life Sci, Jinju 660701, South Korea 3.Cent Mindanao Univ, Coll Agr, Dept Soil Sci, Maramag, Philippines 4.Gyeongsang Natl Univ, Div Appl Life Sci, BK 21 Program, Jinju 660701, South Korea
Recommended Citation:
Kim, Gil Won,Gutierrez-Suson, Jessie,Kim, Pil Joo. Optimum N rate for grain yield coincides with minimum greenhouse gas intensity in flooded rice fields[J]. FIELD CROPS RESEARCH,2019-01-01,237:23-31