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

Abstract

In this paper, field trials in two soils with different N min were conducted to study the effects of mineral N content (N min) 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 N min had a remarkable influence on the MYNR in the first spring cabbage season. The MYNR for spring cabbage lessened in the soil with high N min. Soil N min 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 N min. 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 N min 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 N min 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 quality of vegetable produce.