Abstract: 【Objective】 Taking sweet corn as a catch crop, the accumulation of nitrate in soil profile under different root layer regulation and control measures and their influence on growth of succession cucumber were studied. 【Method】 Sweet corn was planted in the fallow season of the traditional greenhouse in the North China Plain. Using traditional cultivation as the control, a field plot experiment was conducted with 2 root layer regulation and control measures: adding soil conditioner and straw returning to field. The experiment was carried out from May 2008 to May 2011, a total of three sweet corn-cucumber crop rotation, six crops were planted. Sweet corn was planted from early June to September every year, and cucumber seedlings were reared from the early October to the end of January next year. Cucumber plants were planted in early February the same year. In the sweet corn season, three treatments were conducted and arranged at random with three replications. The plot size was about 4 m×2 m, plot interval was 0.3 m, and 1 m of guard rows were laid out between plots. 【Result】In the sweet corn planting seasons, the highest grain yields were obtained in soil conditioner treatment and the yields were 6.2, 7.4 and 7.9 t·hm^-2 in 2008, 2009 and 2010. The total N uptake rate in soil conditioners and straw returning to field treatments was higher than the traditional planting. After planting sweet corn for three seasons, straw and soil conditioner treatments promoted the growth and development of root system in 20-60 cm soil layer and enhanced root to absorb nutrients from deeper soil. Both the two treatments reduced the NO₃^--N of soil profile, especially the subtraction of NO₃^--N in 100-200 cm of the crop root zone, the NO₃^--N subtractive trend roughly was soil conditioner＞straw returning of field＞the traditional planting. After cucumber harvest in three seasons, the differences in cucumber yield, the biomass and nitrogen uptake were not significant, the average soil NO₃^--N residue of three seasons in 0-200 cm was in the order of straw returning of field＜soil conditioner＜the traditional planting. After three cropping seasons, the nitrogen surplus in 0-200 cm soil layer in the traditional planting, soil conditioner and straw returning to field treatments was, respectively, 1 911.6, 1 966.83, and 1 930.2 kg·hm^-2, and conditioning treatment was significantly higher than that of traditional planting. 【Conclusion】In the greenhouse soil with high nitrate accumulation, along with the increasing length of planting, adding soil conditioner to soil and appropriate straw returning to field, the subtraction of NO₃^--N in 100-200 cm of the crop root zone was more than traditional planting. Planting catch crops significantly decreased the effects of soil NO₃^--N in soil of the succession cucumber. Soil conditioners and straw returning to field can significantly improve the ability of sweet corn to decrease soil NO₃^--N, slow soil NO₃^--N leaching, and improve economic returns.

Key words: root layer regulation, greenhouse vegetables, the rotation system of sweet corn and cucumber, NO₃^--N accumulation