Kuroda Hisao1, Lin Xiaolan2, Kitamura Tatsumi3, Oouchi Takao3 and Sugaya Kazuhisa3
1 College of Agriculture, Ibaraki University, 3-21-1, Chuuo, Ami-town, Inashiki, Ibaraki, 300-0393, Japan, http://www.agr.ibaraki.ac.jp/, hisao.kuroda.agr@vc.ibaraki.ac.jp
2 United Graduate School of Agricultural Science Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-city, Tokyo 183-8509, Japan
3 Ibaraki Kasumigaura Environmental Science Center, 1853 Okijyuku Tsuchiura-city Ibaraki 300-0023, Japan.
Abstract
Lake Kasumigaura is the second largest lake in Japan and it is eutrophic. Nutrient loads from agriculture and livestock waste have been identified as a possible cause. Of particular concern are increasing nitrogen concentrations in the Hokota River, where pig farming is a major enterprise. The Japanese government has been advocating conservation measures such as a reduction in the use of chemical fertilizers and synthetic pesticides. As a result, organic forms of nutrients were believed to be good for the environment and less harmful than chemical fertilizers. However, incorrect application of nutrients in any form may contribute to nitrogen pollution. We propose that increasing nitrogen concentrations in Hokota River results from excessive application of swine manure to upland fields, as there has not been an increase in the amount of mineral fertiliser applied. Similarly, increases in nitrogen concentration were observed in spring water (from ground water to surface water) below an upland field that received a large application of horse manure.
In addition, soil core results from an upland field receiving nitrogen inputs for 30 years and subsequently drained in 2011 showed slow movement of residual soil nitrogen from the profile. As a result, residues of nitrogen remain in the soil from historical nitrogen inputs. Nitrogen leaching from the upper portion from rainfall during the last few years was evident, but slow. These results suggest that there was long-term nitrogen leaching potential due to the influence of the accumulated nitrogen. As a result, it was concluded: 1) Livestock waste or organic fertilizer is a likely significant contributor to nitrogen pollution. 2) Nitrogen water quality signatures lag behind the application of organic nitrogen (manure). 3) the infiltration of nitrogen from the soil in upland fields is driven by rainfall.