Nitrate Accumulation And Related Control Strategies In The Open-Field Vegetable Production Of Beijing Suburb

On the basis of the eight-season vegetable rotating experiments (1999-2001), the open field experiments with rotating system of cauliflower (Brassica oler. L., var secalinuni) - catch crops including sweet corn (Amaranthus spp.) and amaranth (Zea mays L.) - spinach (Spinacia oleracea L.) were conducted in Beijing suburb in 2002, in order to study the dynamic change of nitrate leaching affected by different water and nitrogen inputs. Balanced irrigation and fertilization treatments were introducer', in the experiments of cauliflower and spinach, in comparison with conventional nitrogen and irrigation practices. Catch crops were involved in the experiment in summer season without any nitrogen application and water treatments. Crop biomass, marketable yield and soil NO3"-N accumulation were investigated to understand the growth of catch crops and the effects on extracting nitrate from deep soil layers. The main results were as follows:There was no significant difference in crop yield under different water and nitrogen treatments in cauliflower experiment. However it was found that NO3--N residue in conventional nitrogen treatments in the soil profile of 0~ 180cm was obviously higher than that in recommended nitrogen treatments; water treatments did not significantly influence soil NO3--N residue under the same nitrogen treatments. Generally, NO3--N residue was higher than 150 kg/hm2 N in conventional treatments, lower than 100 kg/hm2 N in recommended nitrogen and water treatments.Sweet corn had good remarkable yield with 9.2-10.2 t/hm2 FW without any fertilizer input. Nitrogen uptake by sweet corn and amaranth ranged from 184 kg/hm2 N to 256 kg/hm2 N. There was no significant difference in spinach yields among water and nitrogen treatments. However spinach yield in the plots after sweet corn harvest and fallowing was significantly higher than that after amaranth.With the extraction of catch crops, NO3-N content in soil layer of 0~90cm was obviously reduced lower than 100 kg/hm2 N, and still high in soil layer of 90~ 180cm. Nitrogen mineralizationand nitrate leaching were strong in fallow treatments. After spinach harvest, NO3--N content in 60~90cm soil layer was very low, and reduced sharply in 90~ 180cm soil layer under conventional nitrogen and water treatments. NO3--N content in 0-180cm soil layer was basically lower than 100kg/hm2 N, and only 50 kg/hm2 N in 60~ 180cm soil layer under recommended nitrogen and water treatments.