Quantification of methane emissions from Chinese rice fields (Zhejiang Province) as influenced by fertilizer treatment

Methane emissions from rice paddies were quantified by using an automatic field system stationed in Zhejiang Province, one of the centres for rice cultivation in China. The data set showed pronouned interannual variations over 5 consecutive vegetation periods; by computing average values of all experimental plots the annual emissions were 177 g CH₄ m^-2 yr^-1 in 1987, 50 g CH₄ m^-2 yr^-1 in 1988, and 187 g CH₄ m^-2 yr^-1 in 1989. The field preparations encompassed 4 different treatments: (1) no fertilizers, (2) mineral fertilizer (KCl, K₂SO₄), (3) organic manure (rape seeed cake, animal manure), (4) mineral fertilizer plus organic manure. The methane emission rates of the different fertilizer treatments did not show significant differences. The mean emission rates, calculated over the entire observation period of 5 seasons, were 30.4 mg CH₄ m^-2 h^-1 (non-fertilized plot) and 28.3 mg CH₄ m^-2 h^-1 (mineral fertilizers). These values indicate a high level of methane production even without additional input of organic material into the rice-soils. In the other plots, the organic fertilizers were added once per vegetation period at app. 1 t fresh weight per ha, a relatively low application rate by agronomical standards. The mean emission rates were 35.1 mg CH₄ m^-2 h^-1 when manure was applied as sole fertilizer and 27.5 mg CH₄ m^-2 h^-1 when applied jointly with potassium fertilizers. Based on the results of this study we estimate a range of 18-28 Tg CH₄ yr^-1 as the total methane emission from Chinese rice fields. However, more field data from representative sites in China are needed to reduce the uncertainties in this estimate.