PENGARUH JERAMI PADI DAN BAHAN PENGHAMBAT NITRIFIKASI TERHADAP EMISI GAS RUMAH KACA (METANA DAN DINITROGEN OKSIDA) PADA EKOSISTEM SAWAH TADAH HUJAN DI KABUPATEN PATI, JAWA TENGAH

Global warming happens due to the increase of anthropogenic greenhouse gases (GHGs) concentration in atmosphere. Rice soils are regarded as one of major sources of non CO2 GHGs emissions, namely CH4 and N2O. The objectives of rice soil management and lowland rice culture are to increase soil and plant productivities using rice straw incorporation into soil and nitrification inhibitor materials which influence on GHGs dynamics. Research activity was conducted in rainfed lowland areas at Pati Regency during 2009-2010 to determine CH4 and N2O emissions from rainfed lowland rice soil that was applied rice straw and nitrification inhibitor materials under rice cropping of transplanted rice (TPR) and direct seeded rice (DSR). The experiment used design of complete factorial 3X3 that was arranged in randomized complete block design. The treatments were consisted of rice straw factor (without using rice straw, fresh straw, composted straw) and nitrification inhibitor factor (without applying nitrification inhibitor, neemcake, carbofuran). Data observed was fluxes of CH4 and N2O, organic C, nitrate, N uptake, grain yield, soil properties. Methane emission from direct seeded rice was lower than from transplanted rice, namely 58 112 kg CH4 ha -1 season -1 in DSR and 82 192 kg CH4 ha -1 season -1 in TPR, respectively. Nitrification inhibitor could reduce methane emission in DSR, namely as much as 17 kg CH4 ha -1 season -1 with using neemcake and as much as 6 kg CH4 ha -1 season -1 with using carbofuran, respectively. Nitrous oxide emission in DSR was higher than in TPR, namely 58-320 g N2O ha -1 season -1 in TPR and 124-485 g N2O ha -1 season -1 in DSR, respectively. Incorporations of fresh straw and composted straw could reduce N2O emission of 49.2 and 59.9 % (TPR) and 32.9 and 28.2 % (DSR), respectively. Application of neemcake and carbofuran could significantly reduce N2O emission, namely 44.0 and 34.9 % (TPR) and 49.7 and 22.6 % (DSR), respectively. Methane production potential from rainfed lowland rice soil (Inceptisols) correlated positively and significantly with soil organic C content, C/P ratio, C/S ratio, total bacteria l population, and soil respiration, however, it correlated negatively and significantly with availabilities of sulphate, Mn, exchangeable Na in soil. Whereas N2O production potential correlated positively and significantly with soil NO3 - content, Nitrosomonas population, denitrifier population, however, it correlated negatively and significantly with clay content and available Mn in soil. Application of nitrification inhibitor materials reduced potentially emissions of methane and nitrous oxide from rainfed lowland rice soils. The application of organic matter with low C/N ratio into rice soils tended emit lower methane than the high C/N ratio