Effects of Slow-release Nitrogen Fertilizer on Yield and Nitrogen Accumulation of Summer Maize in Shajiang Black Soil Area

[Objectives] This study was conducted to verify the field application effect of slow-release nitrogen fertilizer on summer maize in Shajiang black soil area by simultaneous sowing and fertilization, and explore the application scope and nitrogen metabolism mechanism, so as to lay a foundation for fertilizer reduction and efficiency improvement. [Methods] With maize variety Beiqing 340 and sulfur-coated urea as experimental materials, five nitrogen application levels were set, namely, control (C0), slow-release nitrogen 70 kg/hm^(2) (C70), slow-release nitrogen 140 kg/hm^(2) (C140), slow-release nitrogen 210 kg/hm^(2) (C210) and slow-release nitrogen 280 kg/hm^(2) (C280). The phosphorus and potassium fertilizers were all in accordance with the unified standard. [Results] With the application rate of slow-release nitrogen increasing, the nitrogen accumulation in organs increased first and then decreased after tasseling stage of maize. In order to reduce the fertilizing amount and increase efficiency, 210 kg/hm^(2) of slow-release nitrogen fertilizer was the best fertilizing amount for summer maize in Shajiang black soil area. [Conclusions] This study provides reference for fertilizer reduction, efficiency improvement and sustainable development of summer maize in Shajiang black soil area.

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 quality of vegetable produce.