1ST RECORDS OF A FIELD EXPERIMENT ON FERTILIZER EFFECTS ON METHANE EMISSION FROM RICE FIELDS IN HUNAN-PROVINCE (PEOPLES-REPUBLIC-OF-CHINA)

Fertilizer effects on methane emission from Chinese rice fields were i nvestigated by a praxis-oriented approach applying balanced amendments of N, P and K. The data set obtained covered the emission rates of ap p. one month in early rice and one month in late rice 1991. An interco mparison between the 4 treatments showed pronounced differences in the magnitudes of methane emission rates. The combined organic/mineral fe rtilizer application, commonly used as local farming practice, resulte d in relatively high seasonal averages of methane emission rates (26.5 mg CH4 m-2 h-1 in early rice and 50.1 mg CH4 m-2 h-1 in late rice). T he lowest emission rates were observed in the plot with pure mineral f ertilization (6.5 mg CH4 m-2 h-1 in early rice and 14.3 mg CH4 m-2 h-1 in late rice). Pure organic fertilizers by unfermented substances yie lded the highest methane emission rates of all field trials (38.6 mg C H4 m-2 h-1 in early rice and 56.2 mg CH4 m-2 h-1 in late rice). The fe rtilization with fermented material derived from biogas generators res ulted in substantially lower emission rates than the other trials with organic amendments, the seasonal averages cor-responded to 15.9 mg CH 4 m-2 h-1 (early rice) and 22.5 mg CH4 m-2 h-1 (late rice). Interpreta tion of the results can be obtained from the different potentials of t hese fertilizers for methane production. Based on this concept the dif ferent methane emission rates observed with organic/mineral, pure mine ral and pure unfermented-organic fertilizers could directly be attribu ted to the different quantities of organic matter incorporated into th e soil. The low methane emission. from the plot treated with fermented material could be explained by a depletion of potential methane precu rsors resulting from the preceding fermentation. The results of this i nvestigation provide evidence that the extensive use of specific chemi cal fertilizers and the application of sludge from the operation of bi ogas generators could lead to a net reduction of the methane emission from rice fields.