Underground water contamination and movements of nutrients in soil under sand dune cultivation

本研究旨在明确沙丘栽培土壤中硝酸盐污染地下水的实际情况及硝酸盐在土壤中的运移情况。从1993年8月起每月监测鸟取沙丘周围农田地下地下水硝酸盐浓度。今年，分别位于鸟取县中部和西部的北条和Yumigahama沙丘被增加为监测地点。鸟取沙丘西部（Karo区）为花卉蔬菜生产区，NO_3浓度在10 ~ 40 mgN/L范围内，东部（Yuyama区）为面包房大蒜生产区，NO_3浓度大多在10 mgN/L以下。Karo地区NO_3浓度高的原因可能是大量施肥和鸡舍排放的废水渗入土壤。北条沙丘区是山药和葡萄的重肥区，地下水大部分被硝酸盐污染，浓度在10 ~ 20 mgN/L之间。在由滨沙丘区，也就是韭菜产区，NO_<3->N的浓度大多小于10 mgN/L。利用沙丘土进行了不同灌溉条件下的柱试验，结果表明，灌溉NO_3的淋滤量随灌溉水量的增加而成比例增加。预测如果在目前的土壤管理下，沙丘农田地下水硝酸盐污染将会更加严重。

The research was carried out to clear the actual condition of groundwater contamination with nitrate and the movement of nitrate in soil under sand dune cultivation.Nitrate concentration of groundwater underfarmlands around Tottori sand dune has been monitored every month form August, 1993. This year, Hojo and Yumigahama sand dune , which are located at central and western part of Tottori prefecture respectively, were added as monitoring site.High concentration of NO_3 in the range of 10-40 mg N/L, was always observed in the western area of Tottori sand dune (Karo district), where was the area of flower and vegetable production, while in the eastern area (Yuyama district), where was the area of bakers garlic production, mostly the concentration was less than 10 mgN/L.It seemed that high NO_3 concentration in the Karo district resulted form heavy application of fertilizer and penetration of waste water discharged from hencoop into soil. In the area of Hojo sand dune, where was the area of chinese yam and grape production with heavy application of fertilize , most of groundwater was polluted with nitrate and the concentration of was in the range of 10-20 mgN/L.In the area of Yumigahama sand dune, where was the area of leek production, mostly the concentration of NO_<3->N was less than 10 mgN/L.As a result of the column experiment on various irrigation conditions by using sand dune soil, it was clarified that the amount of NO_3 leached by irrigation increased in proportion to the volume of irrigation water.It was predicted that the contamination of underground water with nitrate became a more serious situation if the current soil management was continued on the sand dune farmland.