Nitrogen Fertilizer Application under Double Cropping Systems of Wheat-Maize Impacting on the Nitrate Contents of Ground Water in North China

Sixty households were surveyed in Jingxian County, Hebei Province, and Xinxiang County, Henan Province, North China. Sampling of ground water from wells showed that nitrate contents were no more than 3 mg l^-1. In contrast, water samples drawn from Huantai County, Shandong Province, and Wenxian County, Henan Province gave nitrate contents for five water samples over the EC standard, reaching 95 mg l^-1. The proportions of samples over standard were 7.1% and 22.2% in Wenxian and Huantai counties, respectively. In these two counties there was a positive relationship between the nitrate in ground water and the nitrogen application rate to the wheat and maize double cropping system. It was also demonstrated that ground water nitrate was negatively related to the depth of the well sampled. Strategies for reducing the nitrate rates of ground water are outlined, including cutting down the quantity of nitrogen applied, adjusting the ratio of NPK and combining the utilization of inorganic fertilizer with organic manures. Considering the need for food security in China and, at the same time, the need to maintain water quality, these steps should be taken without delay.