การประเมินผลกระทบของเกษตรกรรมพื้นที่ลุ่มน้ำตอนบน ที่มีผลต่อดินและคุณภาพน้ำของพื้นที่ลุ่มน้ำยูสิปัง ซองโซตอนล่าง ประเทศภูฏาน

Abstract

The study was conducted in Yusipang and Hongtso Watershed in Bhutan to assess; upstream farming intensification, onsite soil erosion, point source of water contamination, its impact on soil and downstream water quality, and design guidelines for improving the farmland and quality of stream water. The land use and site characteristics were analyzed using GIS software, the information on farming practice, socio-economic condition, use of agrochemicals, soil conservation works, and water use were collected using PRA and RRA tools, 11 households were interviewed for in-depth study. The farmland was divided into four different slope categories (0-4%, 4-8%, 8-12%, 12-16%), and a total of 27 soil samples were collected from different slope classes. 3 soil samples were collected from the nearby forest area using a purposive sampling method to compare the result. The samples were examined in the Laboratory for its texture, macronutrients, pH and organic matter content. The annual soil loss from agriculture land was determined by using the USLE model. The water quality was assessed in four predetermined sample points using a field testing kit, eight parameters were studied. The water sediment testing for the presences of Organophosphate group and Carbonate group was done in the Institute of Product Quality Standardization, Maejo University. The horticulture is the epitome of agriculture practice, farmers grow apple, potato, cabbage, and cauliflower as cash crops. The increasing market demand for agriculture products has forced the farmers to switch over to small commercial farming. Farmers use agrochemicals on a regular basis to upturn the production to meet the increasing demand. The horticulture is the primary occupation of the farmers as it constituents 74% of the total household income. The annual soil loss in the agriculture land varies from 2.15tons/ha/year in the slope class 0-4% to 8.24 tons/ha/year in the slope class 12-16%. The soil is moderately acidic (average pH 5.5), the average Phosphorus (P) and Potassium (K) content are 77.28 mg/kg and 340.66 mg/kg respectively which is very high compared to the accepted standard. The Nitrogen (N) percentage was 0.19 which is on the verge of depletion as compared to ideal agriculture soil condition. The average percentage of organic matter content is very high in both agriculture and forest soil which stands at 10.47 and 10.31 respectively. There is a progressive decline in water quality from upstream towards the downstream. Water acidity level was found to be high near the farmland and sewage from piggery farm has significantly affected the water quality at the outlet. The use of agrochemicals has negatively impacted on the soil quality of the farmland. The stream water quality was influenced by high nutrient residues in the upstream farmland, waste from the labour camp, and the sewage from piggery farm. These sources were found to have significantly contaminated the water rendering it unsafe for human consumption and ecological services. The evidence of high inorganic mineral content in the upstream farmland and increased surface water acidity indicates that upstream farming effects the water quality in the downstream. Amendment of existing soil nutrient imbalance and improving farmland in the upstream was found to be timely and necessary. The Sheng’s technology and Agriculture Land Development Guideline (ALDG) of 2017 are appropriate to conserve topsoil on the slopy land. Use of organic-based fertilizers and biological pest control approach must be promoted to improve agro-ecosystem and reduce water pollution. It is recommended that the sludge from the piggery farm must be treated or converted into useful organic manure.