To achieve appropriate yield levels, inherent nitrogen (N) supply and biological N fixation are often complemented by fertilization. To avoid economic losses and negative environmental impacts due to over-application of N fertilizer, estimation of the inherent N supply is critical. We aimed to identify the roles of soil texture and organic matter in N mineralization and yield levels attained in cereal cultivation with or without N fertilization in boreal mineral soils. First, the net N mineralization and soil respiration were measured by laboratory incubation with soil samples varying in clay and organic carbon (C) contents. Secondly, to estimate the inherent soil N supply under field conditions, both unfertilized and fertilized cereal yields were measured in fields on clay soils (clay 30–78%) and coarse-textured soils (clay 0–28%). In clay soils (C 2.5–9.0%), both the net N mineralization and the cereal yields (without and with fertilization) decreased with increasing clay/C ratio. Moreover, in soils with high clay/C ratio, the agronomic N use efficiency (additional yield per kg of fertilizer N) varied considerably, indicating the presence of growth limitations other than N. In coarse-textured soils, the yield increase attained by fertilization increased with increasing organic C. Our results indicate that for clay soils in a cool and humid climate, the higher the clay content, the more organic C is needed to produce reasonable yields and to ensure efficient use of added nutrients without high N losses to the environment. For coarse soils having a rather high mean organic C of 2.3%, the organic C appeared to improve agronomic N use efficiency. For farmers, simple indicators such as the clay/C ratio or the use of non-N-fertilized control plots may be useful for site-specific adjustment of the rates of N fertilization.

中文翻译：

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土壤有机碳和粘土含量是北方矿质土壤中净氮矿化和谷物产量的决定因素

为了达到适当的产量水平，固有的氮 (N) 供应和生物固氮通常通过施肥来补充。为避免过度施用氮肥造成的经济损失和负面环境影响，估算固有的氮供应量至关重要。我们旨在确定土壤质地和有机质在北方矿质土壤中施肥或不施氮的谷物种植中氮矿化和产量水平的作用。首先，净氮矿化和土壤呼吸通过实验室培养与粘土和有机碳 (C) 含量不同的土壤样品进行测量。其次，为了估计田间条件下土壤的固有氮供应，在粘土（粘土 30-78%）和粗质地土壤（粘土 0-28%）的田间测量未施肥和施肥谷物产量。在粘土（C 2.5-9.0%）中，净氮矿化和谷物产量（不施肥和施肥）都随着粘土/C 比的增加而降低。此外，在粘土/碳比高的土壤中，农艺氮利用效率（每公斤肥料 N 的额外产量）变化很大，表明除氮外还存在生长限制。在质地粗糙的土壤中，通过施肥获得的产量增加随着有机碳的增加而增加。我们的结果表明，对于凉爽潮湿气候下的粘土，粘土含量越高，需要更多的有机碳来产生合理的产量并确保有效利用添加的养分而不会对土壤造成大量的氮损失。环境。对于平均有机碳含量相当高（2.3%）的粗土，有机碳似乎可以提高农艺氮的利用效率。对于农民来说，