A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Development

Thesis (M.Eng.) - Asian Institute of Technology, 1998

This study was conducted to evaluate the mass balance of nutrient on the paddy field in tropical areas. Seven ha of paddy field was selected to investigate total amount of fertilizer input and output. Fertilizer dose that farmer applied for paddy field was found though questionnaire. Total amount of nitrogen against the required nutrient for growing up was 11.05 kg/ha, but total amount fertilizer P was higher than requirement that plant uptake is 2.63 kg/ha at average of applied ferilizer. On other hand, residue inorganic nitrogen and phosphorus retained in the soil layer was 1.32 ppm and 4.46 ppm respectively. At 85% probability, the residue of inorganic nitrogen and phosphorus was 4.9 ppm and 1.1 ppm, respectively (assume density of soil at 0-20 cm below depth was 1.4) The experiment results revealed that the total amount of fertilizer applied on paddy field 116.8 kg N/ha, 46.8 kg P20 5, 50 kg K/ha and 1,400 kg farmyard/ha. On other hand, concentration of nutrient (T-N, T-P) on the water drainage are 17.5 and 0.11 mg/l, respectively. And the residue of nitrogen and phosphorus was 12.38 kg/ha and 2.7 kg/ha, respectively. The concentration of arsenic on drainage channel and on vegetable growing area (0.0022 mg/l) is higher both the concentration of arsenic on pond and drainage channel of paddy field (0.0017 mg/l). Based on the result, this study could suggest some methodology to reduce the effect of agrochemical on human being and environment. Such as policy method (improve awareness of farmer, fertilizer subsidy, soil testing program) and cost of good agriculture practice (use farmyard fertilizer, slow release fertilizer)