Faculty of Environmental Sciences and Natural Resource Management, NMBU, Norwegian University of Life Sciences, Norway.
Faculty of Environmental Sciences and Natural Resource Management, NMBU, Norwegian University of Life Sciences, Norway; Presently Norwegian Centre for Organic Agriculture, 6630 Tingvoll, Norway.
Sci Total Environ. 2022 Jul 1;828:154059. doi: 10.1016/j.scitotenv.2022.154059. Epub 2022 Feb 23.
Emissions from crop residues contribute largely to the total estimated NO emissions from agriculture. Since low soil pH increases NO production by impairing the last denitrification step, liming has been suggested as a mitigation strategy; however, it may also increase NO emissions by enhancing mineralization and nitrification. To gain field-based empirical knowledge, we measured NO fluxes with an autonomous field-flux robot in limed and control plots before and after autumn ploughing of 3-year-old grass, clover grass or red clover swards under different N fertilization regimes. Dolomite applied before establishing the swards raised soil pH from ~4.8 to ~5.8 in limed plots. Higher pH halved emissions from ploughed leys despite higher soil mineral N contents. It also reduced emissions before ploughing. We observed substantial NO fluxes after ploughing, with peaks during a relatively warm wet period after freezing and higher peaks during diurnal snow melt over frozen soil. Average NO fluxes were strongly positively correlated with high herbage yields in the preceding growing seasons rather than with the presence of clover. The yield-scaled average NO fluxes were strongest in low pH soils at all yield levels; this was a true effect of soil pH on NO, as herbage yields were not increased by liming. Here, yield-scaled flux was defined as the average NO flux after ploughing divided by the dry matter. Fluxes in red clover plots were similar to those in grass plots, despite the lower C/N ratio and higher total amount of N in clover residues. However, clover in mixtures with grass increased yields and NO emissions. This suggests that higher ley production enhanced microbial activity, including nitrifiers and denitrifiers, and that the pH effect on facilitating complete denitrification to N overrode any effect on mineralization and nitrification, thus resulting in NO mitigation.
作物残茬的排放是农业中氮氧化物总排放量的主要贡献源之一。由于低土壤 pH 值会通过损害反硝化的最后一步来增加氮氧化物的产生，因此石灰处理被认为是一种缓解策略；然而，它也可能通过促进矿化和硝化作用来增加氮氧化物的排放。为了获得基于田间的经验知识，我们在 3 年生草地、三叶草草地或红三叶草草地的秋季犁耕前后，使用自主田间通量机器人在施石灰和对照小区中测量了氮氧化物通量，这些草地分别处于不同的氮肥管理模式下。在建立草地之前施用的白云石将石灰处理小区的土壤 pH 值从约 4.8 提高到约 5.8。尽管土壤矿质氮含量较高，但较高的 pH 值将翻耕草地的排放量减少了一半。它还减少了犁耕前的排放量。我们观察到犁耕后有大量的氮氧化物通量，在冻结后的相对温暖湿润期和冻结土壤上的白天融雪期间有较高的峰值。平均氮氧化物通量与前几个生长季节的高牧草产量呈强烈正相关，而与三叶草的存在无关。在所有产量水平下，低 pH 值土壤的产量标准化平均氮氧化物通量最强；这是土壤 pH 值对氮的真实影响，因为石灰处理并没有增加牧草产量。在这里，产量标准化通量被定义为犁耕后平均氮氧化物通量除以干物质。尽管红三叶草残茬的 C/N 比和总氮含量较高，但红三叶草小区的通量与草地小区的相似。然而，草地与三叶草的混合物增加了产量和氮氧化物的排放。这表明较高的草地产量增强了微生物活性，包括硝化菌和反硝化菌，而 pH 值对促进完全反硝化生成氮气的影响超过了对矿化和硝化作用的影响，从而实现了氮氧化物的缓解。
