Nitrate leaching has been widely studied in agricultural cropping systems, whereas there are few studies of dissolved organic nitrogen (DON) leaching. Moreover, the factors determining variation of DON leaching in arable cropping systems remain unclear. Here, we examined variations in DON leaching from two organic crop rotations (Organic with Green Manure (OGM) and Organic with Grain Legume (OGL)) and one conventional rotation (Conventional with Grain Legume (CGL)) with and without the use of cover crops and animal manure application. These treatments were part of long-term experiments conducted at three sites in Denmark with different soil types and precipitation. Measurements were conducted in 2008 at all three sites (Jyndevad, Foulum and Flakkebjerg), and 2015 and 2017 at Foulum. We found that the total annual nitrogen (N) leaching ranged from 6.0 to 113.1 kg ha−1 yr−1 at the three rotations. DON leaching ranged from 1.6 to 11.6 kg ha−1 yr−1 under different crop rotations, accounting for 4.5–37.0 % of the total N leaching. The largest DON leaching (about 10 kg N ha−1 yr−1) was found on coarse sandy soil with high rainfall (Jyndevad) and the lowest DON leaching (about 1 kg N ha−1 yr−1) on sandy loam with low rainfall (Flakkebjerg). In the long-term experiment with loamy sand and medium rainfall (Foulum) in 2015 and 2017, cover crops reduced DON leaching in most cases, while manure had no significant effect on DON leaching. On average across different treatments in 2015 and 2017 at Foulum, grass-clover showed the lowest DON leaching (3.3 kg ha−1 in OGM rotation), whereas faba bean had the highest DON leaching (6.5 kg ha−1 in OGL rotation and 6.2 kg ha−1 in CGL rotation). The results demonstrate that DON leaching should be considered when assessing N leaching losses from agricultural cropping systems, in particular when assessing the effectiveness of N mitigation measures that largely affect nitrate leaching and not the losses of DON.

中文翻译：

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丹麦长期有机和常规作物轮作中溶解有机氮的浸出


硝酸盐浸出已在农业种植系统中得到广泛研究，而对溶解有机氮 （DON） 浸出的研究很少。此外，决定耕作系统中 DON 淋溶变化的因素仍不清楚。在这里，我们研究了两种有机作物轮作（有机与绿肥 （OGM） 和有机与谷物豆类 （OGL））和一种常规轮作（常规与谷物豆类 （CGL））的 DON 浸出变化，有和没有使用覆盖作物和动物粪便施用。这些处理是在丹麦的三个地点对不同土壤类型和降水进行的长期实验的一部分。2008 年在所有三个地点（Jyndevad、Foulum 和 Flakkebjerg）以及 2015 年和 2017 年在 Foulum 进行了测量。我们发现，在三个轮换中，年总氮 （N） 浸出量在 6.0 至 113.1 kg ha-1 yr-1 之间。在不同作物轮作下，DON 浸出量为 1.6 至 11.6 kg ha-1 yr-1，占总氮浸出量的 4.5-37.0%。在降雨量大的粗沙质土壤 （Jyndevad） 上发现了最大的 DON 浸出量（约 10 kg N ha-1 yr-1），在降雨量低的沙壤土 （Flakkebjerg） 上发现了最低的 DON 浸出量（约 1 kg N ha-1 yr-1）。在 2015 年和 2017 年对肥沃沙和中等降雨量 （Foulum） 的长期试验中，覆盖作物在大多数情况下减少了 DON 淋失，而粪污对 DON 淋失没有显着影响。在 2015 年和 2017 年的不同处理中，Foulum 的平均 DON 浸出量最低（OGM 轮作中为 3.3 kg ha-1），而蚕豆的 DON 浸出量最高（OGL 轮作中为 6.5 kg ha-1，CGL 轮作中为 6.2 kg ha-1）。 结果表明，在评估农业种植系统的氮浸出损失时，特别是在评估主要影响硝酸盐浸出而不是 DON 损失的氮缓解措施的有效性时，应考虑 DON 浸出。