Effects of organic and N fertilizers on methane production potential in a Chinese rice soil and its microbiological aspect

An incubation experiment to determine the effects of organic and chemical N fertilizers on methane (CH(4)) production potential in a Chinese flooded rice soil was conducted. Organic matter, added as rice straw and organic manure, increased CH(4) production rate significantly. Chemical N fertilizers such as ammonium bicarbonate (AB), modified ammonium bicarbonate (MAB), and urea (U) did not show a clear effect when they were applied with rice straw. Field results may be very different because of the involvement of rice plants. Organic manure showed different promoting effects on CH(4) production rate. Pig manure stimulated the production rate most, followed by chicken and cattle manure. This difference in organic manure was not related to either total C added to the system or to C/N. The study on bacteria groups related to CH(4) production indicated that the different effects of organic matter may be closely related to content of easily decomposable organic matter. A significant linear relationship between CH(4) production and the logarithm of the number of zymogenic bacteria was found with an r value of 0.96. This finding suggests that the number of zymogenic bacteria may be used as an index to predict CH(4) production potential in flooded rice fields and other wetlands.