THE CONTRIBUTION OF RICE FARMING ON NITROGEN ENRICHMENT IN YEH SUNGI WATERSHED, TABANAN BALI - Alit Artha Wiguna, I Wayan; Lansing, J. Stephen; Adnyana, Oka (Jurnal Pengkajian dan Pengembangan Teknologi Pertanian, 2003)
Pelaksanaan program intensifikasi pertanian melalui konsep revolusi hijau membuat meningkatnyaproduksi padi secara dramatis sehingga pada tahun 1984 Indonesia mencapai swa-sembada beras. Uniknya, sebelumtahun 1984 Indonesia dikenal sebagai negara pengimpor beras yang terbesar di dunia. Akan tetapi, disampingprestasi yang spektakular dalam produksi padi, dalam beberapa hal revolusi hijau juga memberi kontribusi dampakyang tidak menguntungkan terhadap ekosistem.Perkembangan pertanian di Bali, khususnya sawah sangat terkaitdengan sistem subak. Subak adalah pengaturan air irigasi tradisional di Bali yang telah dilaksanakan sejak berabadabadyang lalu. Sehubungan dengan masalah di atas, penelitian ini telah dilaksanakan di Daerah Aliran Sungai(DAS) Yeh Sungi di Kabupaten Tabanan, daerah di bagian barat Bali. Daerah penelitian meliputi delapan subakyaitu: Subak Apit Yeh and Subak Uma Poh di daerah hulu tempat tangkapan air; Subak Padangakitan, Jaka, Sungi I,Bena, dan Subak Tangkub di daerah tengah; dan Subak Gde Gadon I di daerah hilir. Penelitian ini dilakukan selama12 bulan, mulai dari bulan April 2001 hingga Maret 2002. Tujuan penelitian adalah: (1) meneliti tingkat pengayaanhara nitrogen di air irigasi yang berkaitan dengan aplikasi intensif pupuk anorganik di berbagai sistem pertaniandalam sistem subak di Bali; (2) meneliti kualitas lingkungan air, berkaitan dengan tingkat pengayaan hara nitrogendi dalam air irigasi. Hasil penelitian menunjukkan bahwa pengayaan hara pada air irigasi berkaitan dengan sistempertanian pada sistem subak. Tingkat pengayaan hara di daerah hulu lebih tinggi daripada di daerah tengah dan hiliruntuk N-NO3-; untuk memelihara kelangsungan ekosistem Subak, maka aplikasi pupuk N harus mempertimbangkankandungan hara tersebut dalam air irigasinya. Pelaksanaan pertanian telah menyebabkan pengayaan hara nitrogenyang berlebihan di daerah irigasi, khususnya di daerah tengah maupun hilir yang masing-masing didominasi olehpola pertanian padi-padi-padi dan padi-padi-palawija. Untuk memelihara kelangsungan ekosistem subak, makaaplikasi pupuk nitrogen harus mempertimbangkan kandungan hara di air irigasi.Kata kunci: sistem pertanian padi, pengayaan air irigasi, ekosistem subak.Â The implementation of agricultural intensification program through the green revolution concept has madethe increasing rice production dramatically and in 1984 Indonesia achieved ice self-sufficiency. Uniquely, before1984 Indonesia was known as the biggest rice importing country in the world. However, beside of spectacularachievement in rice production, green revolution to some cases also contributes less favorable impact to theecosystem. The agricultural development in Bali, particularly rice field is closely related to the subak system. Subakis a traditional model of irrigation water treatment in Bali practiced since centuries ago. The related to abovementionedissues, this research has been conducted at Yeh Sungi watershed in Tabanan District, western part ofBali. The research site includes eight subaks: Subak Apit Yeh and Subak Uma Poh at upstream area of catchmentsarea; Subak Padangakitan, Jaka, Sungi I, Bena, and Subak Tangkub at the middle area; and Subak Gde Gadon I atdownstream area. This research was carried out for 12 months between April 2001 and March 2002. The objectionof this research were: (1) to investigate the water enrichment level of N nutrients in the irrigation water related to theintensive application of inorganic fertilizers at various farming systems in subak system in Bali; (2) to investigatethe water environment quality, related to the water enrichment level of N nutrient in the irrigation water. Research96Jurnal Pengkajian dan Pengembangan Teknologi Pertanian Vol. 6, No. 2, Juli 2003 : 95-106results showed that nutrient enrichment on irrigation water related to farming system on subak ecosystem. The levelof nutrient enrichment at upstream (hulu) area is higher than the middle (tengah) and downstream (hilir) areas for N-NO3-.To maintain the sustainability of subak ecosystem, therefore the application of N fertilizer should considerthose nutrients content in irrigation water. The agricultural practice has caused excessive enrichment of N nutrientsin irrigated area, especially at the middle as well as downstream areas dominated by rice-rice-rice and rice-ricepalawija(second crop) cropping patterns.Key words: rice farming system, water enrichment, subak ecosystem.