Study On Nitrate Status Of Groundwater And Nitrogen Uptake By Catch Crop In Greenhouse In Suburbs Of Beijing City

In facility vegetable field of North China, over input of nitrogen fertilizer is regarded as the common phenomena, which always results in nitrate accumulation in soil and has the potential to infect surrounding groundwater. From August 2009 to December 2010, this study was investigating many families with greenhouse, collecting agricultural power-operated wells' water samples, screening test and comparison experiments in the suburbs of Beijing in order to raise the utilization rate of nitrogen and to reduce nitrogen leaching in soil of facility vegetable field. The main results are as follows:1.Results obtained from agricultural power-operated wells'investigation in 5 districts of the suburbs of Beijing such as Daxing, Fangshan, Mentougou, Tongzhou, Changping show that the (average) nitrate content in groundwater in the 234 samples randomly collected is 3.6 mg/L. Using the national drinking water standard as evaluation indexes, this includes: 12.4% of the wells exceed the limit (above 10 mg/L) and 0.8% of wells seriously exceed the limit (above 10 mg/L) in NO3--N content. NO3--N content in groundwater is higher in facility vegetable field than in crop field, and NO3--N content in groundwater is increasing as growing age increases. 17.6% of the wells exceed the limit (above 10 mg/L) and 23.5% of wells achieve qualified (but on alert status). In addition, NO3--N content decreases in groundwater with groundwater depth increasing.2.The screening test of five catch crops such as sweet corn (Zea mays L.), sorghum hybrid Sudan grass, herbst bloodleaf (Iresine herbstii Hook.), water spinach (Ipomoea aquatica Forsk.) and wheat (Triticum aestivum L.)had been carried out during the summer fallow period to make sure of different effects of different catch crops. The result shows the biomass and nitrogen absorbed by sweet corn (Zea mays L.) is significantly better than other four catch crop treatments (P<0.05) and is up to 92 335 kg/hm~2 and 330 kg/hm~2 (fig.4), respectively. Nitrogen absorption per plant and N growth rate per plant is significantly higher than other four catch crop treatments (P<0.01). 3. Results from comparison experiments in fifteen typical facility vegetable fields in four areas of Beijing, such as Daxing, Fangshan, Mentougou, Tongzhou show that sweet corn is suitable for facility vegetable field of North China during the summer fallow period from economic benefit and environmental benefit. Planting sweet corn can increase farmers'average income to 30 504.2 yuan/hm2 and can reduce the nitrate nitrogen content in soil profiles efficiently, especially can decrease the risks of the surrounding groundwater.