Assessing the effects of livestock manure application on water environments and modeling water and nitrogen badgets in a watershed

当务之急是防止畜禽粪便对水体的污染，建立合理的处理方法来处理年产9500万吨的畜禽粪便。我们评估了由于将奶牛粪便施于草地表面而造成的地下水和地表水中硝酸盐氮(NO_3)的污染。在过去的三年里，50%到60%的年降水量渗入到土壤中。因此，土壤表面施入的有机肥和化肥(NO_3)很容易被转移到地下水表面，这是一个很大的问题。然而，用时间域反射法测定土壤水分和硝酸盐含量时发现，施入的NO_3主要消耗在地表至约80 cm深的根际地带。土壤取样法提取的土壤水分的化学分析表明，NO_3可能通过反硝化作用、植物吸收和安迪索吸附在根部消耗。由于施有机肥后植物体内的NO_3含量增加，并随着植株的生长而降低，说明植物对NO_3的吸收和消耗。通过对试验田地下水位的观测，发现了试验田地下水的补给。虽然目前地下水中NO_3浓度低于规定水平，但地下水中NO_3浓度有逐渐升高的趋势。因此，假设目前地下水水质变化的趋势和野外管理实践继续下去，地下水中的NO_3浓度可能在大约40年内达到规定的水平。还需要进一步调查，以评估畜禽粪便在草地上施用对地下水质量的长期影响。

It is urgent ot prevent water pollution by livestock wastes and to establish a proper method to process livestock manure which is produced 95 million ton annually. We have assessed ground- and surface- water contamination of nitrate nitrogen (NO_3) due to dairy cattle manure applied to the surface of a grass filed. In the last three years, 50 to 60% of annual precipitation infiltrated into soil. Thus, it is a big concern that manure and fertilizer (NO_3) applied to the soil surface may be easily transorted into the groundwater surface. It was found, however, with measuremet of water and nitrate contents in soil using time domain reflectometry that most of NO_3 applied was consumed in the root zone between the surface and about 80cm deep. Chemical analysis of soil water, extracted from soil samples from the soil coring method, revealed that NO_3 was consumed in the root zone probably by denitrification, uptake by a plant, and adsorption on Andisol. As content of NO_3 in plants increased after the manure application and deceased with the growth of the plants, it was suggestd that NO3 was up-taken and consumed by plants. Observation of groundwater level in the experimental field revealed recharge of groundwater in the field. Although the current concentration of NO_3 is below the regulated level, concentration of No_3 in groundwater tended to increase vary gradually. Thus, assuming the continuation of the current trends of changes in groundwater quality and the management practice of the field, NO_3 concentration in ground water might reach the regulated level in approximate 40 years. Further investigation is needed to assess long-term effects of livestock manure applied to the grass field on groundwater quality.