Effects of different fertilization modes on nitrogen use efficiency of cabbages and nitrogen loss from vegetable field

Conventional fertilization causes soil nitrogen loss and low fertilizer use efficiency in vegetable growing system,and the nitrogen loss also increases the risk on environment.Many researchers have reported a significant decrease of leaching NO3--N losses when the amount of nitrogen applied decreases.However,little efforts have been made on the study of nitrogen loss by surface runoff or by leaching in vegetable field.Therefore,in order to evaluate the effects of different fertilization on the yield of cabbages,the nitrogen use efficiency,the dynamics of nitrogen loss and simultaneously the amount of nitrogen loss by runoff or by leaching and their relative ratios,a series of field experiments in the cabbage fields in Taihu watershed and also the laboratory studies were carried out respectively during September to November,2010. Six modes of fertilization,i.e.,none fertilization(CK),chemical fertilizers(CF),organic manure(OF),special fertilizers(SF)(combined chemical fertilizer and organic manure),reduced amount of special fertilizers by 20%(SF1),reduced amount of special fertilizers by 40%(SF2),were conducted in cabbage growing system in Taihu watershed.Accordingly,the amounts of nitrogen applied were 0,256,256,256,205and 154kg/hm2, respectively.The experimental design was the randomized complete block with triplications,each plot of which was 17.5m2(5m×3.5m). The results showed that the yield of cabbages was SF SF1 CFSF2 OF CK.While compared with the chemical fertilizer and organic manure,the special fertilizers significantly increased the yields by 31.84%and 50.31%(P 0.05),respectively.The agronomic efficiency of nitrogen(NAE)was SF1 SF2 OF CF SF CK.The physiological efficiency of nitrogen(NPE)was OFSF1 CFSF2 SFCK.The nitrogen uptake was SFSF1 SF2 CF OF CK.There was no significant difference in nitrogen uptake among different fertilization modes.The nitrogen use efficiency was 10.55%-24.17%.Significant differences(P0.05)were found in nitrogen use efficiency, which increased significantly from 16.72% to 24.17% with the amount of nitrogen applied decreased,among different special fertilizers(SF,SF1 and SF2).The total nitrogen loss was 13.11-40.66kg/hm2,the descending order of which for all the treatments was:CFSF OFSF1 SF2 CK.The main way of N loss in the cabbage field was by surface runoff,which accounted for 90.92%-94.42% of total nitrogen loss.The nitrogen loss by leaching surface runoff was significantly correlated with fertilization and leaching amounts,while the surface runoff was slightly impacted by fertilization and rainfall,and the ratio of leached N/fertilizer N was only 0.21%-0.56%.Nitrate was the main form of N loss 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 by 7.43kg/hm2.Among the special fertilizers,SF2 decreased the total nitrogen loss by 12.02kg/hm2 compared with SF treatment. 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 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 by 20%is the environment-friendly way of fertilization for sustainable cabbage growing systems.