Fates of fertilizer nitrogen and gaseous N loss in maize fields in China.

Maize (Zea mays L.) is one of most important crops in China, and its cultivation increasedrapidly in the last decades. High doses of nitrogen (N) fertilizers are widely applied for highgrain yield. Quantifying the fates of fertilizer N, especially the use efficiency by abovegroundbiomass (NUE) and their losses to the environment and the atmosphere, is critical for localagricultural management. However, up to now, it is not clear on fate of N fertilizer and howand how much the applied nitrogen is lost, particularly by the various forms of gaseousN. We have conducted six new 15N tracer experiments and combined previous results toevaluate the fates of N fertilizer in maize cropping systems across China. In order to accuracyevaluate the gaseous N loss, a fully automated measuring system was built to simultaneouslymeasure soil N2O and NO emissions in 2017 and 2018 for a typical maize filed in NortheastChina; to identify the source (soil N or fertilizer N) of gases of NO, N2O and NH3,another field experiment was conducted in the adjacent field using 15N-labeledfertilizer. We found that, on average, 34%, 35% and 31% of the applied N fertilizer (averagely 222kg N ha−1, n = 23) was taken up by crop, retained in the soil and lost to the environment,respectively. The results of the automated measuring system showed that the release ratesof NO and N2O were 9.1 and 2.6 kg N ha−1 in 2017, 2.6 and 2.2 kg N ha−1in2018, respectively. Relatively high NO emission rate in 2017 might been caused byrelatively low annual precipitation in that year (437 mm in 2017 and 581 mm in2018). The results of the static chamber system showed that the release rates of NH3,NO and N2O during the maize growing period were only 1.6, 1.8 and 1.4 kg Nha−1, respectively, while NO and N2O emission using this method being muchlower compared to the auto system with high resolution. 15N labeling experimentshowed that 67%, 52% and 29% of the released NH3, NO and N2O came fromthe applied fertilizer N. Seasonal patterns of soil NO and N2O emissions weresimilar, indicating they were controlled by similar factors. Among the factors, soiltemperature and moisture were significantly related to the emissions of NO and N2O,and soil temperature was significantly controlling the NO/N2O ratio in this studysite. Key words: nitrogenous gases losses, maize crop, nitrogen fertilization, 15N trace,nitrogen use efficiency (NUE) [ABSTRACT FROM AUTHOR]