Abstract Catch crops may strongly reduce nitrate leaching during autumn and winter in temperate climates. Authorities therefore aim to stimulate farmers to place catch crops in their rotations by allowing them to apply more nitrogen (N) to their fields. Furthermore, some regulations make it possible to fertilize catch crops after harvest of specific crops such as winter cereals, even if catch crops are sown during late summer. Some farmers claim that this practice is essential for a good development of the catch crop. However, it is not sure whether this summer fertilization to catch crops could result in any additional nitrate leaching, compared to nitrate leaching under non-fertilized catch crops. We therefore designed field experiments including four different catch crop species, each of them sown after harvest of winter cereals at two different dates, and each of them receiving two different doses of pig slurry or receiving no fertilizer at all. Experiments were installed on sites with different soil textures in northern Belgium. Based on the results of soil mineral N and N uptake, we assessed the risk of additional nitrate leaching caused by fertilization of catch crops. We found that the apparent uptake of N released from pig slurry was rather limited but sufficient to avoid additional nitrate leaching on sandy soils, mainly due to supplementary immobilization of the applied N occurring during mineralization of the cereal crop residues. It is critical to mention the limiting conditions that we found to be adequate from our results: catch crops were to be sown in good circumstances before September and could only receive the smallest dose of pig slurry, which was approximately 60 kg N ha−1. On silty soils, however, we found even under these conditions a few indications of small amounts of additional nitrate leaching. As fertilization did not seem mandatory to develop an effectively functioning catch crop and as there was no indication of reduced nitrate losses due to this practice, we would rather discourage fertilization of catch crops to exclude any environmental risk. However, fertilization significantly increased the catch crop yield, so the decision to fertilize or not may also be seen as a trade-off between minor amounts of additional nitrate leaching and enhanced biomass-related effects, such as the additional input of organic carbon into the soil.

中文翻译：

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冬季谷物收获后用猪粪施肥的作物下额外硝酸盐浸出的风险评估

摘要 在温带气候下，秋季和冬季捕捞作物可以大大减少硝酸盐的浸出。因此，当局旨在通过允许农民向田地施用更多氮 (N) 来刺激农民轮作种植作物。此外，一些法规允许在收获特定作物（例如冬季谷物）后对捕获作物施肥，即使捕获作物是在夏末播种的。一些农民声称，这种做法对于捕获作物的良好发展至关重要。然而，与未施肥的作物下的硝酸盐浸出相比，目前尚不确定今年夏季的作物施肥是否会导致任何额外的硝酸盐浸出。因此，我们设计了包括四种不同捕获作物品种的田间试验，他们每个人在两个不同日期收获冬季谷物后播种，每个人都接受两种不同剂量的猪粪或根本不接受肥料。在比利时北部具有不同土壤质地的地点进行了实验。根据土壤矿物质 N 和 N 吸收的结果，我们评估了由捕捞作物施肥引起的额外硝酸盐浸出的风险。我们发现从猪粪中释放的氮的表观吸收相当有限，但足以避免沙质土壤上额外的硝酸盐浸出，这主要是由于在谷类作物残留物矿化过程中发生的施用氮的补充固定。重要的是要提到我们从结果中发现足够的限制条件：捕捞作物应在 9 月之前在良好的条件下播种，并且只能接受最小剂量的猪粪，约为 60 kg N ha-1。然而，在粉质土壤上，即使在这些条件下，我们也发现了少量额外硝酸盐浸出的迹象。由于施肥似乎不是开发有效运作的捕捞作物所必需的，而且由于这种做法没有减少硝酸盐损失的迹象，我们宁愿不鼓励对捕捞作物施肥，以排除任何环境风险。然而，施肥显着提高了作物产量，因此施肥与否的决定也可能被视为少量额外硝酸盐浸出和增强的生物量相关效应之间的权衡，例如将有机碳额外输入到土壤。