Evaluation of Erosion Rates as Indicators of Ecosystem Services in Bali's Subak Rice Fields: Insights from Tabanan Regency, Indonesia

Soil erosion causes an irreversible loss of soil fertility.The land use which is most affected by erosion is rice fields.This research aims to determine the rate of erosion in Subak in Tabanan Regency and analyse the environmental services provided by Subak.Environmental services are defined as services provided by ecosystem functions whose value and benefits are felt by humans.Subak is a traditional farming organization which is owned by the farming community in Bali Province, Indonesia, and specifically regulates the management and irrigation systems for every rice field in Bali.The research case studies were Subak Kedampal, Subak Sigaran and Subak Bongan.The method used in this research was to take soil samples from each Subak rice field, then calculate the erosion hazard using the Universal Soil Loss Equation (USLE).The Geographic Information System (GIS) was used to intersect the erosion parameters; namely, the rain erosivity factor, soil erodibility factor, slope factor, ground cover vegetation, plant management and conservation action factors, in order to create a soil erosion map.The results show that these three Subak rice fields had very low erosion rates.Subak Bongan has an erosion rate of 0.967 tonnes/ha/yr, Subak Sigaran one of 3,415 tonnes/ha/yr and Subak Kedampal one of 7,714 tonnes/ha/yr.These conditions were benefitted the Subak rice fields as a food supplier, a groundwater recharge area, a provider of environmental education, a recreation and agrotourism area, and as a way to control air pollution and preserve the ecosystem.Compared to rice fields outside Bali which are not managed by Subak, the erosion rate that occurs is higher because irrigation management and specific sloping land management carried out by Subak are able to reduce the level of erosion.