Kontribusi sistem usahatani padi sawah terhadap pengkayaan hara nitrogen, fosfor dan kalium aliran permukaan pada ekosistem subak di Bali: kasus daerah aliran sungai Yeh Sungi di Tabanab Bali

Abstract

Sejak revolusi hijau dimulai, Indonesia mampu meningkatkan produksi pangan, khususnya beras secara spektakuler, sehingga tahun 1984 mampu berswasembada beras, yang sebelumnya sebagai salah satu negara pengimpor beras terbesar di dunia. Penerapan intensifikasi pertanian, selain telah memberikan banyak keberhasilan, ternyata juga memberikan dampak yang kurang menguntungkan terhadap keseimbangan ekosistem, seperti terjadinya pengkayaan hara N, P, dan K pada perairan, karena penerapannya yang kurang tepat. Di Bali pengembangan sektor pertanian, khusus untuk tanaman padi memiliki hubungan yang sangat erat dengan sistem subak. Subak adalah organisasi tradisional pemakai air irigasi, yang sudah ada sejak berabad-abad yang lalu. Penelitian dilakukan di kawasan DAS Yeh Sungi, Kabupaten Tabanan, Bali, meliputi delapan subak yaitu subak Apit Yeh dan Uma Poh di daerah hulu; subak Padangakitan, Jaka, Sungi I, Bena dan subak Tungkub di daerah tengah; dan subak Gde Gadon I di daerah hilir, selama 12 bulan (April 2001-Maret 2002). Penelitian bertujuan untuk: (1) merumuskan tingkat pengkayaan hara N, P, dan K perairan terkait dengan penggunaan pupuk anorganik pada berbagai pola usahatani dalam ekosistem subak dan peluang pemanfaatannya kembali; (2) merumuskan mutu lingkungan perairan, terkait dengan tingkat pengkayaan hara N, P, dan K pada air mgasi. Hasil penelitian menunjukkan, bahwa telah terjadi pengkayaan hara perairan yang terkait dengan sistem usahatani pada ekosistem subak di Bali. Tingkat pengkayaan hara nitrat di daerah hulu lebih tinggi dibandingkan dengan daerah tengah dan hilir. Namun, tingkat pengkayaan hara, fosfat dan kalium di daerah tengah dan hilir lebih tinggi dibandingkan dengan daerah hulu. Namun, mutu lingkungan perairan di daerah hulu lebih rendah dibandingkan daerah tengah dan hilir. Oleh karena itu, untuk menjaga keseimbangan ekosistem subak, rekomendasi penggunaan pupuk N, P, dan K sebaiknya mempertimbangkan kandungan hara tersebut dalam air irigasi, berdasarkan neraca hara, melalui konsep 3R (reused, recycling dan redused). Selanjutnya nilai-nilai THK, khususnya yang terkait dengan pelestarian lingkungan agar dijadikan dasar dalam pembangunan pertanian di Bali.

The implementation of agricultural intensification program through the green revolution concept has made the increasing rice production dramatically and in 1984 Indonesia achieved rice self-sufficiency. Uniquely, before 1984, Indonesia known has 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 irrigated water management in Bali that has been practiced since centuries ago. Related to above-mentioned 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 up stream area of cathcment area; Subak Padangakitan, Jaka, Sungi I, Bena and Subak Tangkub at middle area; and Subak Gde Gadon I at down stream area. This research was carried out for 12 months between April 2001 and March 2002. The objectives of this .research, were, (1) investigates the water enrichment level of N, P, and K nutrients in the irligated water related to the intensive application of inorganic fertilizer at various farming system in Subak system in Bali, (2) investigates the water environmental quality, related to the water enrichment level ofN, P, and K nutrient in the irrigated water. Research results showed, that nutrient enrichment on irrigated 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) area for N-NO3-, but for P-Po/- and K+ ion at the middle and downstream was higher than upstream. To maintain the sustainability of Subak ecosystem, therefore the application of N, P, and K fertilizer should consider those nutrients content in irrigated water. The agricultural practice has caused excessive enrichment of N, P, and K nutrients in irrigated area, especially at the middle as well as down-stream area that dominated by rice-rice-rice and rice-rice-palawija cropping patterns. To maintain the sustainability of subak ecosystem, therefore the application ofN, P, and K fertilizer should consider those nutrients content in irrigated water. Nevertheless, values of Tri Hita Karana especially in relation to environmental safety as the main component of Palemahan should be implemented in agricultural planning and development program.