The effectiveness of detention basin in Soursoup (Annona muricata L.) farming land of Selopamioro village - Bantul, Yogyakarta

Soursop fruit is rich in health benefits. The soursop plants (Annona muricata L.) have a great potential to be cultivated in Indonesia. It requires an enough water availability in the land to optimize biomass production through photosynthesis. Soursoup farming in dry land Selopamioro Village - Bantul, Yogyakarta needs irrigation. Due to geomorphological condition, water resources for irrigation mainly from harvested rainfall in detention basin (local name "rorak'"). This study was aimed to determine the effectiveness of detention basin Soursop farming land in storing the rainfall which later used them for irrigation. The material includes the coordinates of the research location, Soursop farming land boundaries, and detention basins. Furthermore, the daily climate data in the form of rainfall, temperature, net solar radiation, wind speed, atmospheric pressure and relative humidity were used to calculate reference evapotranspiration. The reference evapotranspiration (ETo) was computed by Penman-Monteith approach. Later, it was used to determine plant evapotranspiration (ETc) using the soursop plant coefficient (Kc) from previous study. The effectiveness of detention basins was evaluated from water balance analysis. It was applied to assign annual irrigation water requirement in Soursop farming land. This study defined average ETo of Soursop farming land in Nawungan orchard was 5.0 mm/day, while the average ETc was 3.0 mm/day. There were three detention basins in Soursop farming land, laid on the upper slope and two on the middle slope. Annual irrigation water requirement was 4287 m3;. During this period, three detention basins could meet the water need of plant for 84 days. So, more detention basin should be built in Soursop farming land - Nawungan orchard.