中国科学院沈阳应用生态研究所方运霆研究员团队在我国玉米农田系统中开展了6个原位15N示踪试验，并比较了我国玉米系统肥料氮在东北和华北两个区域的利用和损失的差异。相关成果发表于Soil and Tillage Researh（IF=4.675）。
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Highlights
·23 site-year field experiments were collected to analyze the fates of fertilizer N.
·Uptake, soil remaining and loss, each making up about one-third of fertilizer N fate.
·Regional NUE difference were controlled more by soil properties (vs. climate).
·64% of maize N was derived from soil implies native soil N is an important N source.
·External N replenishment to soil N consumption is vital to long-term fertility of soil.
Abstract
Maize (Zea mays L.) is a staple crop that is grown worldwide. The heavy use of nitrogen (N) fertilizers in maize cropping systems has resulted in low N use efficiency (NUE) and even caused N pollution in some regions of China. To evaluate the environmental impacts of over-fertilization, it is essential to reveal NUE and the fates of the applied N fertilizers, which can be accurately quantified only by the field 15N tracer technique. In this study, we conducted six on-farm 15N tracer experiments with four in Northeast (NE) China where maize is extensively cropped. We combined the results from these field experiments with previous 15N tracer results (most in the North-Central (NC) region) to estimate the fates of N fertilizer in maize cropping systems throughout China. In total, there were 23 site-year field experiments. We found that, on average, 34%, 35% and 31% of the applied N fertilizers (222 kg N ha−1 on average) was taken up by aboveground biomass, retained in the soil and lost to the environment, respectively. The NUE, as the percentage of 15N removal by aboveground biomass, was much higher in NE China than in NC China (47% vs. 28%, n = 6 and 16, respectively). The regional NUE differences suggested that the overall NUE in the Chinese maize cropping system would be underestimated if only data from NC China were considered. Additionally, NE China had a higher crop N uptake (260 vs. 192 kg N ha−1) and a lower N loss proportion (21% vs. 34%) than NC China. These regional differences were controlled more by soil properties than by climatic factors. In addition to fertilizer N, our 15N results indicated that, on average, 64% of the maize N was derived from soil, implying that native soil N is also an important N source for crop N uptake. Based on the mass balance of N input and N output, exogenous N replenishment to soil N pool consumption is a vital mechanism for maintaining the long-term fertility of the soil. To evaluate the long-term fates and use efficiency of N fertilizer, future research needs to quantify the contribution of N fertilizer to soil N consumption - replenishment.
施氮是增加和维持农作物产量的重要农艺措施。但是，过量施氮不仅浪费资源，造成土壤退化，还会污染水体和大气。明确施入农田氮肥的去向和利用效率是农田氮肥管理的基础。受土壤类型、气候条件、田间管理等因素的影响，不同区域和不同作物之间氮肥去向存在很大差异。认识这些差异以及控制因素可以帮我们更好地管理氮肥，提高利用效率，减少损失和污染。玉米是我国重要的农作物之一，其在我国的种植规模不断扩大，种植面积和产量早已超过小麦、水稻等农作物，其中在我国东北增长最为迅速。然而，有关玉米农田肥料氮利用效率和损失的研究多集中在华北区域，东北较少。由于气候和水土条件的差异，东北地区玉米农田氮肥的利用效率和损失可能与其他种植区不同。
中国科学院沈阳应用生态研究所稳定同位素生态学实验室与国内外多家单位合作，在我国玉米农田系统中开展了6个原位15N示踪试验（—，其中4个在东北），并结合文献中的数据，比较了我国玉米系统肥料氮在东北和华北两个区域的利用和损失的差异。研究发现施入当季氮肥作物平均吸收利用为34%，35%残留在土壤，31%损失（进入水体和大气）。其中作物吸收利用和损失表现出明显的地域差异，东北地区的吸收比例要显着高于华北地区（47% vs. 28%），而损失比例则低于华北地区（21% vs. 34%）。东北区域氮利用效率较高的原因可能是该地区玉米产量显着高于华北地区，从而导致更高的氮吸收（260 vs. 192 kg N ha-1）。与气候因子相比，土壤性质差异可能是造成氮肥去向区域差异更重要的原因。此外，研究还发现当季作物吸收氮素中来自当季肥料仅占36%，说明绝大多数玉米吸收的氮素来自非肥料氮（64%），包括土壤自身的矿化和硝化供氮。因此，为了维持土壤的长期供氮能力以及农田生态系统的氮平衡，应重视土壤原有氮的消耗和补偿。
