ชื่อเรื่อง PHOSPHORIZATION AND SURFACE WATER RISK ASSESSMENT FOR RICE FIELD ผู้ดำเนินการ Orathai Sukreeyapongse*, Chuchitt Sagwansupyakorn, Darunee Chaiyarojana Chanida Charanworapan and Lamai Srisawat บทคัดย่อ          Phosphorus is an important nutrient for plant growth. It is a critical component in agriculture since a sub-optimal levels of available P in soil limits the growth of plants. Although most Thai soils are inherently deficient in P, in some areas farmers have applied P until many soils are sufficient or have a high P content. Consequently, water draining from these fields are also high in P, resulting in increased growth of algae and other plants in surface water. P has become known as a key contributor in the eutrophication of water bodies. Farmers do not need to add P when soils are sufficient in P. They can reduce cost of P fertilizer and prevent loss of P. To assess the problem of surface wastewater from phosphorization in rice fields associated with different practices, soil samples and data were collected from 14 studied sites through out the country which are representative of soils used for growing rice in Thailand. (Sample and data collecting from this sub-project were from the integrated project run by sustainable rice project committee.) Each studied site has 12 treatments with different chemical fertilizer ratios, green manure and bio-substance extract and these treatments can be grouped into 6 groups which were farmer practice (FP), control (C), chemical fertilizer and green manure (CG), chemical fertilizer and bio-substance extract (CB), chemical fertilizer and green manure and bio-substance extract (CGB) and green manure and bio-substance extract (GB). Phosphorus index (PI) for every rice field was calculated and used as surface wastewater risk assessment. The results showed that PI for FP, C, CG, CB and CGB were 16-34.5, 5-22, 13-25.3, 11-25, 13-25 and 7-16, respectively. There is one studied site showed medium level of P loss and another site that showed high levels of P loss. For holistic approach for rice fields in Thailand, it can be concluded that rice fields are not non-point sources of water pollution.

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