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Abstract
Asparagus fields in Nong Ngu Lauem village, Nakhon Pathom province, Thailand, were surveyed for the cultural practices adopted, yield, fertilizer use, nutrient accumulation in soils, and nitrate-nitrogen concentration of the underground water. In this village, asparagus is being cultivated under contract farming with a Japanese agribusiness company and 60% of the product is exported to Japan. Average application rates of nitrogen- and phosphorus-fertilizers were 840 kg N and 286 kg P ha−1 year−1, and less than 5% of the applied elements was recovered in the harvested products. Phosphorus accumulated in the surface 20 cm soil significantly, unlike N determined by the Kjeldahl method. Higher concentration of nitrate-nitrogen was detected down to 1-m depth in the asparagus fields compared with the adjacent sugarcane fields. Underground water samples were taken from 15 wells of the village and their content of nitrate-nitrogen was determined once a month during a period of 18 months. Nitrate-nitrogen was distributed unevenly among the wells, and no periodic peaks in the concentrations were detected. The highest value of 39 g nitrate-nitrogen m−3 was recorded.
