Study On N/P Use Efficiency By Cabbages And Their Losses From Vegetable Fields Under Difrerent Fertilization Modes

Conventional fertilization caused soil nitrogen and phosphorus loss and low fertilizer use efficiency in vegetable growing system, the nitrogen and phosphorus loss also increase the risk on environment. In order to evaluate the effects of different fertilization on the yield of cabbages, the nitrogen and phosphorus use efficiency, the dynamics of nitrogen and phosphorus loss and simultaneously the amount of nitrogen and phosphorus lost by runoff or by leaching and their relative ratios, a series of field experiments and also the laboratory studies with six modes of fertilization, i.e., none fertilization (CK), chemical fertilizers (CF,256kg/hm2), organic manure (OF,256kg/hm2), special fertilizers (SF,256kg/hm2, combined chemical fertilizer and organic manure), reduced amount of special fertilizers by20%(SF1,205kg/hm2), reduced amount of special fertilizers by40%(SF2,154kg/hm2), were carried out in cabbage growing systems in Taihu watershed. The results obtained are as follows:(1) Fertilizer application can significantly increase the yield of cabbages. The yield of cabbages was SF> SF1> CF> SF2> OF> CK. While compared with the chemical fertilizer and organic manure, the special fertilizers significantly increased the yields by31.84%and50.31%(P<0.05), respectively. SF1and SF2could reduce the yield of cabbages, SF1could reduce the production of cabbages while the reduction of yield for SF2was not obvious.(2) The agronomic efficiency of nitrogen (NAE) was SF1> SF2> OF> CF> SF> CK. The physiological efficiency of nitrogen (NPE) was OF> SF1> CF> SF2>SF> CK. The nitrogen uptake was SF> SF1> SF2> CF> OF> CK. There was no significant difference on nitrogen uptake for different fertilization modes. The nitrogen use efficiency was10.55%-24.17%. Significant differences (P<0.05) were found in nitrogen use efficiency, which increased significantly from16.72%to24.17%with the amount of nitrogen applied decreased, among different special fertilizers(SF, SF1and SF2). (3) The total nitrogen loss was13.11-40.66kg/hm2, the descending order of which for all the treatments was:CF> SF> OF> SF1> SF2> CK. The main way of N loss in the cabbage field was by surface runoff, which accounted for90.92%-94.42%of total nitrogen loss. The nitrogen lost by leaching was significantly correlated with fertilization mode and leaching amounts of water, while the surface runoff was only slightly impacted by fertilization mode and rainfall, and the ratio of leached N/fertilizer N was only0.21%-0.56%. Nitrate was the main form of N lost in surface runoff while the ammonium was the main one in leachate. Compared with the chemical fertilizers, the special fertilizers decreased the total nitrogen loss by7.43kg/hm2. Among the special fertilizers, SF2decreased the total nitrogen loss by12.02kg/hm2while compared with SF treatment.(4) The TP loss for six fertilization modes ranged from0.030to0.112kg-hm-2, and the TP lost by runoff only accounted for0.045%～0.120%of total loss. The descending order for TP runoff loss were:CF>OF>SF>SF1>SF2>CK. The correlation among CF, OF and SF on the TP loss by runoff was significant. Applied levels of phosphate fertilizer had significant influence on the TP runoff loss for SF、SF1and SF2. The descending order of TP leaching loss were:CF>SF>SF1>OF>SF2>CK. The TP lost by leaching was significantly influenced by the applied levels of phosphate fertilizer for SF、SF1and SF2(R2=0.9439).(5) The nitrate content of cabbages for different fertilization modes were:CF> SF>SF1>SF2>OF>CK. The nitrate content of cabbages under tested fertilization modes could not meet with the A hygienic standard for vegetables and the Green-Labled vegetables based on Chinese Standards. The VC content for6fertilization modes ranged from388.35to462.80mg-kg-1, and the soluble sugar content ranged from1.05%to1.43%. OF could significantly increase the VC content and soluble sugar content than other modes. Although the amount of fertilizer applied for SF1and SF2were less than other fertilization modes, the VC content and soluble sugar content of cabbages for SF1and SF2were still higher than that of CF. It is concluded that the special fertilizers and the reduced amount of nitrogen applied are beneficial to the increase of nitrogen use efficiency by cabbage and the decrease of the nitrogen loss from the vegetable field, hence being helpful to protect the water environment in Taihu watershed. Based on the above research results, we can conclude that the reduced amount of special fertilizers by20%is the environment-friendly way of fertilization for sustainable cabbage growing systems.