Effect of Nitrogen Fertilization on Methane Flux in a Structured Clay Soil Cultivated with Onion in Central Hokkaido, Japan

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This study was conducted to investigate the effect of N fertilization on the soil CH_4 flux during the growing season of onion in a structured clay soil with stagnant water at depths of 70-80 cm and with a peat-mixed subsoil. The following 4 treatments were analyzed over a period of two years: T1) fertilized, onion growing, T2) fertilized, bare field, T3) unfertilized, onion growing, and T4) unfertilized, bare field. In the fertilized T1 and T2 treatments, fertilizers (mixture of 3 : 1 NH_4NO_3 : (NH_4)_2SO_4) at rates of 322 kg N ha^-1 in 1999 and 242 kg N ha^-1 in 2000 were applied as basal fertilizers before onion was transplanted. CH_4 fluxes among the treatments ranged from -0.06 to 0.12 mg CH_4-C m^-2 h^-1 in 1999, and from -0.03 to 0.01 mg CH_4-C m^-2 h^-1 in 2000, which were high after heavy rain in summer. Cumulative CH_4 flux from May to November in the fertilized T1 and T2 treatments was 59 mg CH_4-C m^-2 for both treatments in 1999, and 3.2 and -0.9 mg CH_4-C m^-2 in 2000, respectively. On the other hand, in the unfertilized T3 and T4 treatments, the cumulative CH_4 flux was 0.2 and -9.2 mg CH_4-C m^-2 in 1999, and -26 and -20 mg CH_4-C m^-2 in 2000, respectively. Although the cumulative CH_4 flux in each treatment was higher in 1999 than in 2000, the fertilized treatments in both years showed a significantly higher cumulative CH_4, flux than the unfertilized treatments. This might be ascribed to the higher level of nitrification in the fertilized treatments, because a high nitrate concentration was observed in the fertilized treatments in the onion growing season. The results also revealed that onion growing did not exert a significant influence on the CH_4, flux. The precipitation from May to November was 642 mm in 1999 and 1,008 mm in 2000, and the CH_4 emission increased when the precipitation was low. In addition, the CH_4 concentration in the soil profile increased with the increase of the depth in summer as the soil was dry. These findings indicated that CH_4, diffusion from the soil to the atmosphere was inhibited by rainwater.
社団法人日本土壌肥料学会の論文

Effect of Nitrogen Fertilization on Methane Flux in a Structured Clay Soil Cultivated with Onion in Central Hokkaido, Japan

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