PENGARUH PEMBERIAN PUPUK HAYATI PENAMBAT NITROGEN PADA EMISI GAS N2O DI PERTANIAN LAHAN KERING
ENDAH RETNANINGRUM, Prof. Dr. Irfan. D.Prijambada, M.Eng.; Prof. Dra. Sukarti Moeljopawiro, M.App.Sc, Ph.D.
2014 | Disertasi | S3 Ilmu BiologiDalam upaya mengenalkan pupuk hayati penambat nitrogen pada petani, dilakukan penelitian mengenai pengaruh pemberian pupuk hayati penambat nitrogen yang dikombinasikan dengan pupuk nitrogen pada emisi gas N2O di pertanian lahan kering. Lokasi penelitian berupa lahan tanaman jagung (Zea mays. L.) dan kacang tanah (Arachis hypogaea L.) yang dilakukan di Ngawen, Kabupaten Gunungkidul, Yogyakarta, Indonesia (110° 40ʹ 48.52ʹʹ E, 7° 50ʹ 34.20ʹʹ S, 240 m asl). Perlakuan yang diberikan terhadap kedua lahan tersebut berupa pemberian kotoran sapi, kotoran sapi yang ditambah pupuk hayati penambat nitrogen, urea, urea yang ditambah dengan pupuk hayati penambat nitrogen, dan kontrol (tanpa pemberian pupuk N). Urea dan kotoran sapi dengan konsentrasi N yang setara diberikan di kedua lahan sebanyak 3 kali selama periode penelitian yaitu 12, 30, dan 48 hari setelah tanam (HST), masing-masing sebanyak 44, 29, dan 15 kg ha-1 urea dan 6.000, 4.000, and 2.000 kg ha-1 kotoran sapi. Emisi N2O diambil dengan menggunakan closed-chamber method pada 24, 42, 60, dan 72 HST, kemudian jumlahnya ditentukan menggunakan gas kromatografi. Pada waktu yang sama kandungan N tersedia (NH4 +-N and NO3 --N), C organik, lengas tanah dan pH dianalisis. Aktivitas dan keragaman mikrobia tanah penghasil gas N2O dianalisis pada waktu diperoleh hasil emisi N2O tertinggi. Konsentrasi NH4 +-N dan NO3 --N ditentukan dengan kolorimetri setelah masing-masing diekstraksi dengan menggunakan 1 M KCl dan 0,5 M K2SO4. Konsentrasi C organik ditentukan dengan Walkly Black Method. Aktivitas mikrobia pendenitrifikasi dan penitrifikasi penghasil gas N2O masing-masing ditentukan dengan perlakuan acethylene 10 Pa dan O2 100 KPa. Keragaman mikrobia tanah penghasil N2O dianalisis dengan real time qPCR yang dikombinasikan dengan T-RFLP profiling menggunakan gen 16S rDNA. Pada waktu panen, biomasa tanaman dikoleksi untuk analisis berat kering tanaman, hasil biji dan indeks panen. Emisi N2O pada kedua lahan dengan penambahan pupuk hayati penambat nitrogen lebih rendah daripada tanpa penambahan pupuk hayati penambat nitrogen (P<0,01). Korelasi positif diperoleh antara emisi N2O pada kedua lahan dengan konsentrasi NO3 --N, NH4 +-N, C organik dalam tanah (P<0,01), akan tetapi tidak diperoleh korelasi dengan pH dan lengas tanah. Rerata N2O kumulatif yang diproduksi mikrobia dan aktivitas mikrobia total, mikrobia pendenitrifikasi dan penitrifikasi penghasil gas N2O dalam sampel tanah terpilih pada kedua lahan yang mendapat penambahan pupuk hayati penambat nitrogen lebih rendah daripada kontrol (P<0,01). Pemberian pupuk hayati penambat nitrogen pada kedua lahan juga menyebabkan profil T-RFLP fingerprint yang spesifik, yaitu terjadi penurunan jumlah T-RFs dan kenaikan intensitas relatif T-RFs. Pemberian pupuk hayati penambat nitrogen bersamaan dengan kotoran sapi dan urea menaikkan berat kering, hasil biji dan indeks panen kedua tanaman secara signifikan dibanding tanpa penambahan pupuk hayati penambat nitrogen (P<0,01). Dengan ini dapat disimpulkan bahwa pemberian pupuk hayati penambat nitrogen bersamaan dengan pupuk N dapat menurunkan emisi N2O, aktivitas mikrobia total, mikrobia pendenitrifikasi dan penitrifikasi yang berkontribusi terhadap emisi tersebut. Pemberian pupuk hayati penambat nitrogen juga menaikkan berat kering tanaman, hasil biji, indeks panen tanaman jagung dan kacang tanah, serta mempengaruhi dinamika populasi bakteri yaitu menurunkan keragaman dan menaikkan kemelimpahan populasi bakteri tanah.
In an effort to introduce nitrogen fixing biofertilizer to farmers, it was conducted research on effect of nitrogen fixing biofertilizer application combined with nitrogenous fertilizer on N2O gas emission at upland agriculture.. The experimental site were maize cultivation (Zea mays. L.) and ground nut cultivation (Arachis hypogaea L.) that conducted at Ngawen, Gunungkidul District, Yogyakarta, Indonesia (110° 40ʹ 48.52ʹʹ E, 7° 50ʹ 34.20ʹʹ S, 240 m asl). The treatments were addition of fresh cattle manure, fresh cattle manure added with nitrogen fixing biofertilizer, urea, urea added with nitrogen fixing biofertilizer, and control (no N fertilizer added). Nitrogen contents of the added urea and fresh cattle manure were adjusted to be equal. Urea and fresh cattle manure were given three times throughout the experiment period, i.e. 12, 30, and 48 days after planting (DAP). Urea was given at a rate of 44, 29, and 15 kg ha-1, respectively while fresh cattle manure was given at a rate of 6000, 4000, and 2000 kg.ha-1, respectively. The emitted N2O was collected using a closed-chamber method at 24, 42, 60, and 72 DAP and determined using gas chromatograph. At the same time those same time available N (NH4 +-N and NO3 --N), organic C, moisture, pH were analyzed. The activity and diversity of soil microorganisms producing N2O gas were analyzed at the time with the highest N2O emission result. Soil NH4 +-N and NO3 --N were determined colorimetrically after extraction by 1 M KCl and 0.5 M K2SO4, respectively. Soil organic C content was determined by Walkly Black Method. The activity of denitrified and nitrified microorganisms producing N2O gas were evaluated by acetylene 10 Pa and O2 100 KPa, respectively. The diversity of soil microorganisms producing N2O was analyzed by real time qPCR-combined with T-RFLP profiling with 16S rDNA genes. At the harvesting time, plant biomass were collected for analyzing of plant dry weight, yield and harvest index. The N2O emission from plots receiving nitrogen fixing biofertilizer in both fields were lower compared to that without nitrogen fixing biofertilizer (P< 0.01). Positive correlations were observed between soil concentration of NO3 --N, NH4 +- N, organic carbon, and N2O emission in both field (P<0.01). However soil pH and soil moisture!had no correlations with N2O emission. The average of cumulative N2O production and activity of total, denitrified, and nitrified microorganisms producing N2O gas of selected soil samples of both fields resulted that addition nitrogen fixing biofertilizer were lower than without addition (P<0.01). Addition nitrogen fixing biofertilizer in the fields also induced a specific profiles of TRFLP, reduction of T-RFs number and higher degrees of relative intencity of TRFs. Biofertilizer addition with fresh cattle manure and urea increased productivity and and harvest index of both plant significantly than without biofertilizer addition (P<0.01). From this research, it may be concluded that addition of nitrogen fixing biofertilizer in combination with nitrogenous fertilizer could reduce the field emission, the activity of total, denitrified, and nitrified microorganisms contributed on N2O emission. Addition of nitrogen fixing biofertilizer could also increase plant dry weight, yield, and harvest index of maize and ground nut plant, and affected soil bacterial populations by displaying lower diversity and higher abundance.
Kata Kunci : pupuk hayati, emisi N2O, T-RFLP, hasil biji, mikrobia pendenitrifikasi
