Study on the Optimum N Rates Under Spring Cabbage-Maize-Winter Cabbage Rotation System

In this paper,field trials in two soils with different Nmin were conducted to study the effects of mineral N content (Nmin) in soil on the maximum yield N rate (MYNR),N recovery of cabbage under spring cabbage-maize-winter cabbage rotation system,and the correlation of N fertilization with cabbage yield and quality,and to provide the theoretical basis for N recommendation for high-yield,quality,and safety production of vegetables. The effects of six N rates of 0,90,180,270,360,and 450 kg ha-1 on the yield,N recovery of spring cabbage,maize,and winter cabbage,water-soluble sugar,Vc,and nitrate content of vegetables were observed. The results showed that soil Nmin had a remarkable influence on the MYNR in the first spring cabbage season. The MYNR for spring cabbage lessened in the soil with high Nmin. Soil Nmin could be helpful to N recommendation only for the seasonal growing crop because its effects on the following crop yield was less with the active transformation of soil Nmin. The farmer’s practice was 1.8-3.2 times higher than the MYNR of cabbage resulted in the nitrate enrichment of groundwater. Both N application rate and Nmin in the soil profile affected N recovery,whereas,the relay intercropping maize in the cabbage field increased the N recovery at a higher N application rate. Lower N rate (less than 90 kg ha-1) improved the yield and quality of cabbage at the same time; higher N rates increased cabbage yield,but decreased the quality; extremely high N rates of application deceased both yield and quality of cabbage. It was concluded that the soil Nmin had close correlations with MYNR and N recovery of the seasonal growing cabbage. Although the residual effects of the N fertilizer were obvious in Shajiang black meadow soil,cabbage-maize rotation increased the N recovery in treatments with higher N rates. Considering the effects of N rates on cabbage yield and quality,it is necessary to reduce the N rate and lower the yield target for obtaining a better quali