Inhibition experiments on nitrous oxide emission from paddy soils

Abstract

[1] Rice fields using nitrogen-based fertilizers play an important role in the global N 2 O budget. However, our knowledge is still limited with regard to the mechanisms affecting the N 2 O emission and to the measures that can reduce the emission. This paper reports a study of N 2 O emission from paddy soils. The effects of urea, hydroquinone (HQ, a urease inhibitor), and dicyandiamide (DCD, a nitrification inhibitor) have been studied in pot experiments with and without rice plants and with and without addition of wheat straw. With no wheat straw amendment, all treatments with inhibitors, especially with HQ + DCD, had a much smaller N 2 O emission during the rice growing period than the urea treatment, whereas a substantially increased N 2 O emission was observed from a rice-free soil with inhibitors. The N 2 O emission from the rice-planted soil was exponentially positive correlated with the NO 3 À -N concentration in the rice aboveground biomass. By comparing the total N 2 O emission from the rice-free soil and from the rice-planted soil, we found that urea application alone might induce an apparent plant-mediated N 2 O emission, being 0.39 ± 0.08% of the applied urea N. Wheat straw incorporated into the flooded surface layer soil could increase the plant-mediated N 2 O emission significantly. However, application of HQ + DCD could reduce this emission (0.27 ± 0.08% of the applied urea N, compared with 0.89 ± 0.18% in the urea treatment). It also reduced the N 2 O emission from the rice-free soil and from the rice-planted soil. Stepwise regression analysis indicates that denitrification in the flooded surface layer soil was the main source of N 2 O emission from this wetland rice cultivation, particularly when wheat straw was added. A significantly nonlinear negative relation was found between the N 2 O emission and the CH 4 emission when no wheat straw was added, but it was hard to quantify this trade-off relation when wheat straw was incorporated into the flooded surface layer soil.

Mitigation of N2O and CH4 Emission from Rice and Wheat Cropping Systems Using Dicyandiamide and Hydroquinone

“…Chang et al 1998). It was observed in the treatments with inhibitors that the concentration of NO 3 À in the aerial parts of fresh rice plants was much lower than in the U treatment, especially during the first 50 days of the growing season (data not shown, see Xu et al 2002c). Thus, urease and nitrification inhibitors might limit the excessive uptake of nitrate and consequently reduce N 2 O emission from the plant.…”

“…Figure 6. Trade-off relation between N 2 O and CH 4 emission (both expressed as CO 2 equivalents using a GWP of 296 and 23, respectively) from a rice cropping system (adapted from Xu et al 2002c); filled diamonds represent data points corresponding to experiments with the addition of wheat straw; the other data points come from experiments without wheat straw addition (n = U, s = U + HQ, + = U + DCD, · = U + HQ + DCD); for abbreviations see Table 1.…”

“…The regression models were both significant and could explain 23 and 52% of the variability of the N 2 O emission in the rice cropping system with and Figure 2. N 2 O emission dynamics in a rice cropping system during an 80-day growing period; without wheat straw (top) and with wheat straw (bottom); for clarity the standard errors have been removed; statistical analyses are included in Table 2 (adapted from Xu et al 2002c); for abbreviations see Table 1. Another parameter that might control the magnitude of the N 2 O emission from the paddy ecosystem is the NO 3 À concentration in the rice plants.…”

“…Cumulative N 2 O emissions from the rice cropping system, with and without wheat straw addition during an 80-day growing period (adapted fromXu et al 2002c); 2 g urea and 10 g wheat straw were applied per 2 kg soil; for abbreviations seeTable 1.…”

Effects of Elevated Atmospheric CO2 Concentrations on CH4 and N2O Emission from Rice Soil: An Experiment in Controlled-environment Chambers

“…On a global scale, 36% of the direct N 2 O emissions from agricultural fields results from the application of synthetic N fertilizers (Mosier et al 1998). Most N 2 O emissions are from agricultural uplands; however, rice paddy soils also contribute large amounts of N 2 O emissions to the atmosphere when the paddies are flooded to submerge the plants or are drained for harvesting (Cai et al 1997;Ratering and Conrad 1998;Yan et al 2000;Xu et al 2002).…”