Emission of N2O and CO2 and Uptake of CH4 in Soil from a Satsuma Mandarin Orchard under Mulching Cultivation in Central Japan

Abstract

The flux of nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) from brown lowland soils in a satsuma mandarin (Citrus unshiu Marcow, ‘Silverhill’, 31 years old) orchard located in Okitsu, central Japan facing the North Pacific Ocean, was measured once a week from March 2001 to February 2002 using the closed chamber method. Two categories of treatment, mulching and non-mulching, were used in the experimental field by covering the soil surface with a moisture-permeable and waterproof sheet in the latter half of fruit growing season from mid-September to mid-December in 2001. The annual N2O emission and the amount of total nitrogen fertilized were 93 mg N/m2/year and 27.0 g N/m2/year for the non-mulching treatment and 55 mg N/m2/year and 18.9 g N/m2/year for the mulching treatment, respectively. No significant difference was found in the N2O emission factor between mulching (0.34%) and non-mulching (0.29%) treatment. These emission factors were much lower than the average value (0.62%) for upland fields in Japan and the IPCC default value of 1.25%. On the other hand, a small amount of atmospheric methane was absorbed into the surface soils throughout the year. The annual uptake of CH4 was 24 and 17 mg CH4/m2/year for the non-mulching and mulching treatment, respectively, with no significant difference between the two treatments. Annual CO2 emission with the non-mulching and mulching treatment was 1.45 and 0.89 kg CO2/m2/year, respectively. The difference in the amount of each gas emission between the two treatments was discussed with respect to the soil temperature, water-filled pore space (WFPS), the timing and amount of nitrogen fertilized, and the effect of mulching.