[Effects of Nitrogen Fertilizer Application Times and Nitrification Inhibitor on NO Emission from Potted Maize].

Rational application of nitrogen is an important strategy for increasing yield while reducing environmental pollution due to nitrogen. Pot experiments were conducted to study the effects of different application times on maize yield and soil NO emission under conditions of equal nitrogen content, and to explore the relationship between the abundance of nitrogen conversion functional genes and NO emission. Four treatments were used, namely a control (CK, no urea), one-time application (S1, one application of 0.5 g·kg urea+nitrification inhibitor), two separate applications ［S2, two applications of 0.5 g·kg urea (40% and 60% respectively)］ and three separate applications (S3, 0.5 g·kg urea was divided into three different applications: 20%, 40% and 40% respectively). The results showed that: ① nitrogen application promoted soil acidification, and the degree of soil acidification varied significantly with different application times. More applications of nitrogen led to stronger soil acidification. Nitrogen application significantly increased the ear yield and stem biomass of fresh table maize, but different nitrogen application times may alter soil pH, leading to differences in the degree of nitrogen uptake and utilization in plants. While the S3 treatment significantly reduced soil pH, it also reduced the cumulative nitrogen uptake and utilization in the plants, resulting in a high cumulative NO emission. Compared with the S3 treatment, the yield was 40.21% and 42.55% higher in the S1 and S2 treatments, and the cumulative NO emission decreased by 79.4% and 20.9%, respectively. ② NO emission was positively correlated with the abundance of AOB and genes, which were the main contributors to NO emission. S1 significantly decreased the abundance of AOB and genes and NO emissions, while S2 and S3 significantly increased the abundance of and genes and decreased the abundance of genes after fertilization, promoting NO emissions. Nitrogen application times affect the functional genes of the nitrogen transformation process, and thus affect NO emissions. In conclusion, a one-time application of urea combined with DCD only guarantees high maize yield and improves the efficient use of nitrogen, but also reduces greenhouse gas emissions. Thus, it is the recommended nitrogen fertilization mode for the cultivation of fresh corn in Hainan.