Neraca Air Lahan dan Tanaman Padi di Kabupaten Manokwari Selatan, Papua Barat pada Tahun 2019

Abstract

The rain season of 2019 in South Manokwari comes late indicating the longer dry period. This condition causes a reduction in the water resources availability resulting in a lack of ground water availability (KAT). Lack of ground water can be an obstacle in the cultivation of food crops, especially rice plants on rain-fed land. To evaluate KAT, a water balance model is used to calculate crop water needs and analyze surpluses and deficits. This study analyzes land and rice crop balance with Thornwaite and Mather models in South Manokwari Regency during 2019. Monthly rainfall data and class A pot evaporation were used to calculate Potential Evapotranspiration (ETP). Soil physical data including field capacity (KL) and permanent withering points (TLP) with fine soil texture are secondaryly obtained. The analysis was conducted for KAT, deficits and surpluses as well as the percentage of water available to plants (ATS). The results showed that agricultural land was still in optimal condition in January – August, while for rice plants was below the optimum KAT since August and reached TLP in October. The surplus only occurred in January – February and April – June with a peak in June of 157.8 mm (land) and 136.8 mm (rice). Groundwater decreased since July and continued to decline until December, marked by moderate to low ATS conditions. Groundwater deficit from August - December requires the supply of irrigation water for agriculture.