N2O emission characteristics from the soil in a 'Kuerlexiangli' pear orchard based on 15N tracing

Abstract: 【Objective】In Xinjiang, the cultivation of characteristic fruit trees has become an important means for farmers to increase their income.'Kuerlexiangli'pear is the dominant tree species of Xinjiang's characteristic fruit industry, and has become the dominant industry of characteristic fruit in southern Xinjiang. However, the problems in the production of'Kuerlexiangli'pear is becoming more and more obvious, and the unreasonable fertilization and extensive management are becoming more and more serious, leading directly to waste of resources and environmental degradation. Nitrogen is a necessary nutrient for the growth and development of fruit trees. In some cases, increasing nitrogen application can effectively increase fruit yield and improve fruit quality. In'Kuerlexiangli'pear orchards, unreasonable fertilization and excessive application of nitrogen fertilizer will not only reduce the nitrogen use efficiency, but also increase the nitrogen content in the soil, thus accelerating the Nitrous Oxide (N2 O) emission from the orchard soil. As an important greenhouse gas, N2 O has a potential warming effect, about 190 to 270 times higher than that of CO2.【Methods】Although the15N tracer technique is widely used in the study on nitrogen cycling, the research on the use of15N technology to distinguish N2 O sources is rare. Therefore, the six-year-old'Kuerlexiangli'pear orchard was studied by applying15N tracer technique, and the closed static chamber gas chromatography method was used to monitor the soil N2 O discharge flux, incense accumulation amount and Ndff value (Contribution Rate of15N Urea to Soil Nitrogen Gas Loss) .【Results】Fertilization, irrigation and soil temperature all affected N2 O flux, accumulation and Ndff value in the orchard soil. In the afternoon of the 4 th day after the application of the base fertilizer (April 5 th, 16:00—20:00) , the maximum flux of soil N2 O flux was 0.25 g·hm-2·h-1. The cumulative value of N2 O peaked at the night of April 5 th (20:00—8:00) , which was1.560 g·hm-2. On the 4 th day (June 5 th) after application of the dressing fertilizer, the N2 O emission flux in the afternoon (16:00—20:00) and the N2 O accumulation at the night (20:00—8:00) showed the second peak, which were 0.19 g·hm-2·h-1 and 1.440 g·hm-2, respectively. On the 4 th day (April 5 th) after the application of the base fertilizer, the Ndff value of15N2 O increased significantly in each time period.Among them, the maximum peak value of Ndff of15N2 O (1.12%) appeared in the afternoon (16:00—20:00) .On the 4 th day (June 5 th) after application of the dressing fertilizer, the Ndff value of15N2 O in each time period peaked again. Among them, the Ndff value of the15N2 O peak (1.09%) appeared in the afternoon (16:00—20:00) . The amount of soil N2 O emissions increased significantly during the irrigation period, and the soil N2 O fluxes were expressed as follows: afternoon (16:00—20:00) > noon (12:00—16:00) >morning (8:00—12:00) > night (20:00—8:00) . The accumulation of soil N2 O was expressed as nighttime (20:00—8:00) > afternoon (16:00—20:00) > noon (12:00—16:00) > morning (8:00—12:00) .Regression analysis of soil water content and N2 O flux showed that soil water content explained 76.29%soil N2 O flux, and there was a significant positive correlation with soil N2 O flux (p < 0.001) . However, after 10 days of watering every month, the Ndff value of15N2 O in the soil did not change significantly due to changes in soil water content. The soil temperature change in one day was in the ascending order: afternoon (16:00—20:00) > noon (12:00—16:00) > morning (8:00—12:00) > nighttime (20:00—8:00) , and the N2 O flux in soil was relatively consistent within one day. Regression analysis between soil temperature and N2 O fluxe indicated that soil temperature contributed 82.16% of soil N2 O flux, and showed a significant positive correlation with soil N2 O flux (p < 0.001) . The Ndff value of15N2 O changes in one day was in the ascending order: afternoon (16:00—20:00) > noon (12:00—16:00) > morning (8:00—12:00) > night (20:00—8: 00) , which was consistent with the trend of soil N2 O flux. The Ndff value of15N2 O contributed by15N urea changed like this: afternoon (16:00-20:00) > noon (12:00—16:00) > morning (8:00—12:00) > night (20:00—8:00) . N2 O emission from soil nitrogen was 0.8933 g·plant^-1, accounting for 87.43% of the total loss. The loss of fertilizer was 0.128 4 g·plant^-1, accounting for only 12.57% of the total loss.【Conclusion】There was a significant positive correlation between soil N2 O emission and soil temperature and soil water content (p < 0.001) . Moreover, N2 O emission was mainly due to N2 O emission of soil nitrogen. Nitrogen dioxide emission from soil was affected by many factors. There may be some coupling between these factors and the mechanism needs further studies.