Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo Ward, Kyoto 606-8502, Japan.
Water Sci Technol. 2012;66(5):1074-80. doi: 10.2166/wst.2012.292.
Japanese paddy rice systems commonly adopt the rotation of vegetables, wheat and soybeans with paddy rice. Crop rotation may, however, increase the nutrient load in effluent discharged from the district because more fertilizer is applied to the rotation crops than is applied to paddy crops. We investigated a paddy-field district subject to collective crop rotation and quantified the annual nutrient load of effluent from the district in three consecutive years. The total annual exports of nitrogen and phosphorus over the investigation period ranged from 30.3 to 40.6 kg N ha(-1) and 2.62 to 3.13 kg P ha(-1). The results suggest that rotation cropping increases the effluent nutrient load because applied fertilizer is converted to nitrate, and surface runoff is increased due to the absence of shuttering boards at the field outlets.
日本稻田系统通常采用蔬菜、小麦和大豆与水稻轮作的方式。然而，作物轮作可能会增加该地区污水中的养分负荷，因为轮作作物的施肥量比水稻作物多。我们调查了一个实行集体轮作的稻田区，并在连续三年中量化了该地区污水的年度养分负荷。调查期间，氮和磷的年总出口量范围分别为 30.3 至 40.6 千克氮/公顷和 2.62 至 3.13 千克磷/公顷。结果表明，轮作增加了污水中的养分负荷，因为施用的肥料转化为硝酸盐，而且由于田间出口处没有挡板，地表径流增加。
