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
A. WIHARDJAKA, Prof. Dr. H. Shalihuddin Djalal Tandjung, M.Sc.
2011 | Disertasi | S3 Ilmu LingkunganPemanasan global terjadi disebabkan oleh peningkatan kadar gas rumah kaca di atmosfer akibat aktivitas manusia. Tanah sawah dipandang sebagai sala h satu sumber emisi utama emisi gas rumah kaca non CO2, yaitu CH4 dan N2O. Pengelolaan tanah sawah dan praktik budidaya padi sawah yang bertujuan meningkatkan produktivitas tanah dan tanaman seperti penggunaan limbah jerami padi dan pemberian bahan penghambat nitrifikasi berpengaruh terhadap dinamika gas rumah kaca. Kegiatan penelitian dilaksanakan di lahan sawah tadah hujan di Kabupaten Pati selama 2009-2010 untuk mengkaji emisi CH4 dan N2O dari tanah sawah tadah hujan yang diberi jerami padi dan bahan penghambat nitrifikasi pada pertanaman padi walik jerami dan gogorancah. Percobaan menggunakan rancangan 3X3 faktorial lengkap yang disusun dalam acak kelompok lengkap, dengan perlakuan faktor pertama berupa pemberian jerami padi (tanpa jerami padi, jerami segar, jerami melapuk), dan faktor kedua pemberian bahan penghambat nitrifikasi (tanpa bahan penghambat nitrifikasi, biji mimba, karbofuran). Data yang dikumpulkan meliputi fluk CH4 dan N2O, C organik, nitrat, serapan N, parameter agronomik, hasil gabah, dan beberapa sifat fisika, kimia, biologi tanah. Emisi metana dari pertanaman padi gogorancah adalah lebih rendah daripada dari pertanaman padi walik jerami. Emisi metana dari pe rtanaman padi gogorancah berkisar 58 – 112 kg CH4 ha -1 musim -1 , sedangkan dari pertanaman padi walik jerami berkisar 82 – 192 kg CH4 ha -1 musim -1 . Pemberian bahan penghambat nitrifikasi cenderung meningkatkan emisi metana dari pertanaman padi walik jerami, namum emisi CH4 dari pertanaman padi gogorancah nyata turun dengan pemberian bahan penghambat nitrifikasi, yaitu turun sebesar 17 kg CH4 ha -1 musim -1 dengan pemberian tepung biji mimba dan 6 kg CH4 ha -1 musim -1 dengan pemberian karbofuran. Emisi N2O pada pertanaman padi gogorancah adalah lebih tinggi dibandingkan pada pertanaman padi walik jerami. Emisi N2O pada pertanaman padi walik jerami berkisar 58-320 g N2O ha -1 musim -1 , sedangkan dari pertanaman padi gogorancah berkisar 124-485 g N2O ha -1 musim -1 . Pemberian jerami padi dapat menurunkan emisi N2O, yaitu jerami segar dan jerami melapuk dapat menurunkan emisi N2O masing-masing sebesar 49,2 dan 59,9 % (padi walik jerami) dan sebesar 32,9 dan 28,2 % (padi gogorancah). Pemberian bahan penghambat nitrifikasi nyata menurunkan emisi N2O, yaitu biji mimba dan karbofuran menurunkan emisi N2O masing-masing sebesar 44,0 dan 34,9 % (padi walik jerami) dan sebesar 49,7 dan 22,6 % (padi gogorancah). Potensi produksi metana tanah sawah tadah hujan Inceptisol nyata berkorelasi positif dengan kandungan C organik dalam tanah, nisbah C/P, dan nisbah C/S, populasi bakteri total, dan respirasi tanah, tetapi nyata berkorelasi negatif dengan ketersediaan sulfat, Mn, Na_dd dalam tanah sawah tadah hujan. Potensi produksi N2O tana h sawah tadah hujan Inceptisol nyata berkorelasi positif dengan kandungan NO3 - , populasi Nitrosomonas, dan populasi bakteri denitrifikasi, tetapi berkorelasi negatif secara nyata dengan kandungan lempung dan Mn tersedia dalam tanah sawah tadah hujan. Bahan penghambat nitrifikasi berpotensi menurunkan emisi gas metana dan dinitrogen oksida dari tanah sawah tadah hujan. Pemberian bahan organik dengan nisbah C/N rendah ke dalam tanah sawah cenderung mengemisi metana lebih rendah daripada yang bernisbah C/N tinggi.
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.
Kata Kunci : emisi metana, emisi N2O, jerami padi, penghambat nitrifikasi
