The Capability Of Catch Crop In Uptaking Soil Nitrate Under Greenhouse

This study was conducted for the traditional cropping systems of greenhouse in North China Plain. By using deep root type of catch crops as well as their control measures in root zone to carry on the field home position repairing experiments, this study respectively for one year, three years and short term demonstration experiment in vegetable fallow period. Analyzes the influence that different categories of catch crops, combination repair measures and repair time for soil NO₃^--N leaching, comparison and screening out deep root type catch crops and planting to reduce NO₃^--N leaching of accumulated in deep soil; To reval the characteristics of plant efficient decrease accumulation NO₃^--N in soil profile, and cleared their influence on crop yield in the next quarter and soil profile NO₃^--N, Moreover, it analysised the leaching characteriristics of nitrogen in deep soil to explore the greenhouse vegetables leaching mechanism, providing theoretical basis for reducing the leaching of nitrate loss and prevention of groundwater pollution. The main results are as follows:（1） The sweet corn was the best in biomass, N uptake and the overall density of root length and root dry weight greater than other catch categories; sweet corn has the best subtractive ability. In 0²00 cm, the reduction of NO₃^--N of sweet corn reached 907.87 kg/hm² in one year trial, and there was significant difference in the treatments of sweet corn and achyranthes bidentata intercrop and white chrysanthemum; in three years trial, the cutting ability order were sweet corn >sweet sorghum >amaranth. The reduction of NO₃^--N being respectively 153.8, 605.7 and 56.3 kg/hm² in 2008, 2009 and 2010. It is show that, the sweet corn has a huge network of superficial roots, it can intercept the soil NO₃^--N leaching, ruduce the residues in soil profile, it was the better catch crop in the facility vegetable system.（2） The treatment of coconut shell carbon was the best in biomass and N uptake, respectively was 23.87 t/hm² and 288.46 kg/hm², there was significant difference with traditional cultivation; one quarter root-cutting and coconut shell carbon can promote root system absorb NO₃^--N in 60¹60 cm, the reduction of NO₃^--N being respectively 987.91 and 942.99 kg/hm² in 0²00 cm. Three years trial show that the biomass and N uptake of two root layer regulation higher than traditional cultivation, with the increase of planting years, add soil conditioner and straw returning can reducing the leaching of nitrate, In particular, the capacity was stronger to decrease NO₃^--N of crop root zone in 100²00 cm. During the catch crop planting, the effect of coconut shell carbon, soil conditioner and straw returning is more apparent to lower soil NO₃^--N leaching.（3） With the extension of the planting years, catch crop have little effect on vegetable production and biomass, but also reduce the accumulation of soil NO₃^--N, previous sweet cron and sweet sorghum were the best. In different root layer regulation, it is obvious that planting catch crop can reduce soil NO₃^--N in second year. The cutting ability order were previous straw returning> previous conditioner> previous sweet cron> previous fallow in 0²00 cm. The effects of catch crop provide nitrogen would continue after the end of cucumber’s growing. Previous sweet cron and previous conditioner can reduce the NO₃^--N accumulation in cucumber soil.（4） The inbiomass and N uptake of sorghum-sudangrass were 3.73 t/hm² and 79.81 kg/hm², were significantly higher than sweet corn and carrot. The root length and root dry weight of sweet corn were more prominent in 0²0 cm soil layer, sorghum is more higher below 20 cm; one season later, sorghum is the highest decrease ability of NO₃^--N in 0⁴0 cm soil profile. The cutting ability order were sorghum-sudangrass >sweet corn >carrot >fallow in 0¹00 cm soil layer.（5） Planting catch crop allows farmers to abtain higher economic profit, which is 512⁴1702 yuan/hm². Planting sweet cron will enable farmers obtain higher economic profit in one and three year experiment; the economic profit of sorghum-sudangrass higher than sweet cron, the values were 10550 yuan/hm² and 3413 yuan/hm². In the high nitrate accumulated soil profile, planting sweet cron will obtain ideal result in environmental and economic.