Penentuan Musim Tanam Berdasarkan Perhitungan Neraca Air Lahan di Daerah Saumlaki, Pulau Yamdena

Climate information/data of a region plays an important role in agricultural development in the region, because by utilizing the knowledge of the relationship between crops and climate, forecasts can be made of planting time, harvest time, drought (water deficit), flood (water surplus), pest attack and disease, determining the appropriate type of crop, and so on. The purpose of this study was to assess the presence of soil water and to determine the growing season in the Saumlaki area based on two rainfall conditions. This study used monthly rainfall data for 30 years (1990-2019) as well as other climatic data, such as air temperature, air humidity, sunshine duration and wind speed for 15 years (2005-2019). Computing of the water balance was carried out using Thornthwaite-Mather Method, and determination of growing season using soil water in optimum condition. Based on the calculation of the land water balance in the rainfall conditions there was a 75% chance of being surpassed by the groundwater deficit in the Saumlaki area which lasted for 6 months (June- November), whereas the value increases by 183 mm or 45.52% compared to normal conditions, that was from 402 mm to 585 mm. On the other hand, the groundwater surplus lasted only a month (May) and tended to decrease by 686 mm or 97.03% compared to normal conditions, from 707 mm to 21 mm. The optimum soil water content for plants in rainfall conditions was 75% chance of lasting for 6 months (January-June); 2 months shorter than the normal 8 months (December-July). In conditions of 75% chance of rainfall, the growing season in the Saumlaki area lasted for 7 months (December-June); a month shorter than the growing season in normal rainfall conditions of 8 months (December-July). Keywords: growing season, land water balance, rainfall, Saumlaki area   ABSTRAK Informasi/data iklim suatu tempat berperan penting dalam pengembangan pertanian di wilayah tersebut, karena dengan memanfaatkan pengetahuan tentang hubungan antara tanaman dan iklim dapatlah dibuat prakiraan waktu tanam, waktu panen, kejadian kekeringan (defisit air), banjir (surplus air), serangan hama dan penyakit, penentuan jenis tanaman yang sesuai, dan sebagainya. Tujuan penelitian ini untuk menilai keberadaan air tanah dan menentukan musim tanam di Daerah Saumlaki pada dua kondisi curah hujan. Penelitian ini menggunakan data curah hujan bulanan selama 30 tahun (1990–2019) dan data iklim lainnya (suhu udara, kelembaban udara, lama penyinaran matahari kecepatan angin) selama 15 tahun (2005-2019). Perhitungan neraca air lahan menggunakan metode Thornthwaite-Mather, dan musim tanam ditentukan berdasarkan kondisi air tanah optimum. Berdasarkan perhitungan neraca air lahan pada kondisi curah hujan berpeluang 75% untuk dilampaui, defisit air tanah di daerah Saumlaki berlangsung selama selama 6 bulan (Juni-November) yaitu nilainya bertambah sebesar 183 mm (45,52%) dibandingkan kondisi normalnya, yaitu dari 402 mm menjadi 585 mm. Sebaliknya surplus air tanah berlangsung hanya sebulan (Mei) dan cenderung berkurang sebesar 686 mm (97,03%) dibandingkan kondisi normalnya, yaitu dari 707 mm menjadi 21 mm. Kadar air tanah yang optimum bagi tanaman pada kondisi curah hujan peluang 75% berlangsung selama 6 bulan (Januari-Juni); lebih pendek 2 bulan dibandingkan kondisi normalnya 8 bulan (Desember-Juli). Pada kondisi curah hujan peluang 75%, musim tanam di daerah Saumlaki berlangsung selama 7 bulan (Desember-Juni); sebulan lebih pendek dibandingkan musim tanam pada kondisi curah hujan normalnya 8 bulan (Desember-Juli). Kata kunci : curah hujan, daerah Saumlaki, musim tanam, neraca air lahan