THE CONTRIBUTION OF RICE FARMING ON NITROGEN ENRICHMENT IN YEH SUNGI WATERSHED, TABANAN BALI

Pelaksanaan program intensifikasi pertanian melalui konsep revolusi hijau membuat meningkatnya produksi padi secara dramatis sehingga pada tahun 1984 Indonesia mencapai swa-sembada beras. Uniknya, sebelum tahun 1984 Indonesia dikenal sebagai negara pengimpor beras yang terbesar di dunia. Akan tetapi, disamping prestasi yang spektakular dalam produksi padi, dalam beberapa hal revolusi hijau juga memberi kontribusi dampak yang tidak menguntungkan terhadap ekosistem.Perkembangan pertanian di Bali, khususnya sawah sangat terkait dengan sistem subak. Subak adalah pengaturan air irigasi tradisional di Bali yang telah dilaksanakan sejak berabadabad yang 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 subak yaitu: 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 selama 12 bulan, mulai dari bulan April 2001 hingga Maret 2002. Tujuan penelitian adalah: (1) meneliti tingkat pengayaan hara nitrogen di air irigasi yang berkaitan dengan aplikasi intensif pupuk anorganik di berbagai sistem pertanian dalam sistem subak di Bali; (2) meneliti kualitas lingkungan air, berkaitan dengan tingkat pengayaan hara nitrogen di dalam air irigasi. Hasil penelitian menunjukkan bahwa pengayaan hara pada air irigasi berkaitan dengan sistem pertanian pada sistem subak. Tingkat pengayaan hara di daerah hulu lebih tinggi daripada di daerah tengah dan hilir untuk N-NO3-; untuk memelihara kelangsungan ekosistem Subak, maka aplikasi pupuk N harus mempertimbangkan kandungan hara tersebut dalam air irigasinya. Pelaksanaan pertanian telah menyebabkan pengayaan hara nitrogen yang berlebihan di daerah irigasi, khususnya di daerah tengah maupun hilir yang masing-masing didominasi oleh pola pertanian padi-padi-padi dan padi-padi-palawija. Untuk memelihara kelangsungan ekosistem subak, maka aplikasi pupuk nitrogen harus mempertimbangkan kandungan hara di air irigasi. Kata kunci: sistem pertanian padi, pengayaan air irigasi, ekosistem subak. The implementation of agricultural intensification program through the green revolution concept has made the increasing rice production dramatically and in 1984 Indonesia achieved ice self-sufficiency. Uniquely, before 1984 Indonesia was known as the biggest rice importing country in the world. However, beside of spectacular achievement in rice production, green revolution to some cases also contributes less favorable impact to the ecosystem. The agricultural development in Bali, particularly rice field is closely related to the subak system. Subak is a traditional model of irrigation water treatment in Bali practiced since centuries ago. The related to abovementioned issues, this research has been conducted at Yeh Sungi watershed in Tabanan District, western part of Bali. The research site includes eight subaks: Subak Apit Yeh and Subak Uma Poh at upstream area of catchments area; Subak Padangakitan, Jaka, Sungi I, Bena, and Subak Tangkub at the middle area; and Subak Gde Gadon I at downstream area. This research was carried out for 12 months between April 2001 and March 2002. The objection of this research were: (1) to investigate the water enrichment level of N nutrients in the irrigation water related to the intensive application of inorganic fertilizers at various farming systems in subak system in Bali; (2) to investigate the water environment quality, related to the water enrichment level of N nutrient in the irrigation water. Research 96 Jurnal Pengkajian dan Pengembangan Teknologi Pertanian Vol. 6, No. 2, Juli 2003 : 95-106 results showed that nutrient enrichment on irrigation water related to farming system on subak ecosystem. The level of 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 consider those nutrients content in irrigation water. The agricultural practice has caused excessive enrichment of N nutrients in 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.