Nitrogen balance and groundwater nitrate contamination: Comparison among three intensive cropping systems on the North China Plain

Abstract

The annual nitrogen (N) budget and groundwater nitrate-N concentrations were studied in the field in three major intensive cropping systems in Shandong province, north China. In the greenhouse vegetable systems the annual N inputs from fertilizers, manures and irrigation water were 1358, 1881 and 402 kg N ha −1 on average, representing 2.5, 37.5 and 83.8 times the corresponding values in wheat ( Triticum aestivum L.)–maize ( Zea mays L.) rotations and 2.1, 10.4 and 68.2 times the values in apple ( Malus pumila Mill.) orchards. The N surplus values were 349, 3327 and 746 kg N ha −1, with residual soil nitrate-N after harvest amounting to 221–275, 1173 and 613 kg N ha −1 in the top 90 cm of the soil profile and 213–242, 1032 and 976 kg N ha −1 at 90–180 cm depth in wheat–maize, greenhouse vegetable and orchard systems, respectively. Nitrate leaching was evident in all three cropping systems and the groundwater in shallow wells (<15 m depth) was heavily contaminated in the greenhouse vegetable production area, where total N inputs were much higher than crop requirements and the excessive fertilizer N inputs were only about 40% of total N inputs.