[Methane emission from rice paddy soils as influenced by soil physicochemical properties]

To identify the key soil parameters influencing methane emission from rice paddies, and to quantitatively describe the relationship of methane emission with the soil properties, an outdoor pot experiment with a total of 18 paddy soils sampled from different regions in Jiangsu province was conducted in Nanjing Agricultural University during 2000 rice growing season. Seasonal average rate of CH4 emission for all the 18 soils was 6.42 +/- 2.70 mg.(m2.h)-1, ranging from 1.96 to 11.06 mg.(m2.h)-1, approximately a 5.6-fold difference between the maximum and the minimum. Correlation analysis indicated that the seasonal average of CH4 emission was positively dependent on soil sand content (r = 0.528, p = 0.024) and negatively on soil clay content (r = -0.484, p = 0.042). Negative correlation of CH4 emission against soil total nitrogen (r = -0.449, p = 0.062), available nitrogen (r = -0.611, p = 0.007) and NH4(+)-N(r = -0.649, p = 0.004) was also observed. Copper content of soils has a significant negative impact on CH4 emission. The correlation coefficient (r) of CH4 emission against soil available copper and with total copper was -0.594 (p = 0.009) and -0.547 (p = 0.019), respectively. No clear relationship existed between CH4 emission and soil carbon content. A further investigation suggests that the seasonal average rate of CH4 emission can be quantitatively determined by a linear combination of soil available copper, total manganese, and a ratio of available to total iron (R2 = 0.755, p = 0.0001).