Analysis of Subak Ricefields Soil Fertility Status using Geographic Information System (GIS) in Denpasar City, Indonesia

Soil is a growing medium also functions as a storehouse of nutrients that are needed by plants for growth and production. Decreased soil fertility will cause a decrease in production.  This research was carried out in the Subak rice fields in Denpasar City, Indonesia. Subak is an organization owned by a farming community in Bali that specifically regulates the management of paddy fields, especially traditional irrigation systems. UNESCO - The United Nations Educational, Scientific and Cultural Organization - recognizes Subak in Bali as a World Cultural Heritage. The research objectives are to evaluate the fertility status of Subak rice fields in Denpasar City and to map the fertility status of Subak rice fields using Geographic Information System (GIS). The method for this study including surveying and soil sample analysis in the Laboratory. The parameters observed were soil chemical properties including: CEC, KB, C-Organic, P2O5, available K2O, N-Total, pH and salt content. After the soil analysis are obtained, then evaluation of soil fertility status will be carried out using the Soil Research Center (PPT) technical guidelines. Research results show that soil fertility status can be classified into three statuses, namely high, moderate and low soil fertility status. High soil fertility status includes Subak Buaji, Delod Sema, Paang, Padanggalak, Saba, Temaga, Dalem, Kedua, Lungatad, Petangan, Ubung, Intaran Barat, Kepaon, Kerdung, Panjer, Renon, Banyukuning, Lange, Serogsogan and Subak Tegal Buah. Moderate soil fertility category are found in Subak Anggabaya, Biaung, Kedaton, Peraupan Barat, Poh Manis, Taman, Uma Desa, Uma Layu, Yang batu, Pakel I, Pakel II, Cuculan, Sanur, Sesetan, Sidakarya, Pagutan, Semila and Subak Tegallantang. Meanwhile low fertility status includes Subak Sembung, Subak Mergaya and Subak Intaran Timur. Subak with low soil fertility status has a deficiency in soil organic C-content and low total P nutrients in the soil. Directives for managing low soil fertility status are by addition of organic matter for Subak Pakel II, Pakel I, Mergaya, Kedaton, Taman, Biaung, and Anggabaya. Meanwhile P fertilizer is applied to increase P nutrients in Subak Taman