In the past decade it has repeatedly been shown that agriculture is a significant source of ground- and surface water pollution. Nitrogen losses and nitrogen use efficiency (NUE) are major concerns in agricultural practice and of policy-makers. Rapid intensification of livestock production, a result of the focus on increasing productivity from the 1950s onwards, has contributed to a large increase in nutrient surpluses. Here, we performed a quantitative analysis of the variables influencing the nitrogen use efficiency in Flemish grassland-based farming systems. The analysis was based on the large dataset of the Farm Accountancy Data Network, holding technical and economic data of Flemish farms. A statistical model is proposed by performing multiple regression with several variable selection procedures. Many combinations of variables were studied in 92 models and different criteria were taken into account to select the most adequate combination of variables. This approach focuses on a deep statistical analysis and interpretation of the model. The novelty of this research is the quantification and comparison of the influence of different inputs and other variables in nitrogen use efficiency at the farm level. Our results show that, contrary to current knowledge, a higher nitrogen use efficiency was observed for farms with a higher number of ‘Dairy cows ha⁻¹’, holding the rest of the N inputs constant. A higher stocking density is compatible with a higher agricultural sustainability. It is demonstrated that the amount of milk N produced by added cows is higher than the decrease in milk N produced by each single cow due to a reduced input of feed N per cow. The dairy cow becomes more efficient in the use of N, increasing the farm-gate NUE and the farm sustainability. In the dataset of this study, the variable ‘Dairy cows ha⁻¹’ is more relevant than suggested by previous studies: 1.4 times more relevant than the variable ‘kg of N in fertilisers ha⁻¹’, which is 1.5 times more relevant than ‘kg of N in concentrates ha⁻¹’. According to previous knowledge, the N input variables present a negative sign. Decreasing the N input in fertilisers, concentrates and by-products are recommended actions to increase the NUE. Unexpected interaction effects were found.

中文翻译：

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法兰德斯奶牛场氮利用效率的统计模型

在过去的十年中，一再证明农业是地下水和地表水污染的重要来源。氮的损失和氮的利用效率（NUE）是农业实践和政策制定者的主要关注点。自1950年代以来一直致力于提高生产力，结果是畜牧业生产迅速集约化，这极大地促进了营养过剩的增加。在这里，我们对佛兰芒草地农耕系统中影响氮素利用效率的变量进行了定量分析。该分析基于农场会计数据网络的大型数据集，其中包含佛兰德农场的技术和经济数据。通过使用几种变量选择程序进行多元回归，提出了一种统计模型。在92个模型中研究了许多变量组合，并考虑了不同标准以选择最适当的变量组合。这种方法侧重于对该模型进行深入的统计分析和解释。这项研究的新颖之处在于量化和比较了不同投入和其他变量对农场一级氮素利用效率的影响。我们的结果表明，与当前的知识相反，对于“奶牛”数量较多的农场，氮的利用率更高。这项研究的新颖之处在于量化和比较了不同投入和其他变量对农场一级氮素利用效率的影响。我们的结果表明，与当前的知识相反，对于“奶牛”数量较多的农场，氮的利用率更高。这项研究的新颖之处在于量化和比较了不同投入和其他变量对农场一级氮素利用效率的影响。我们的结果表明，与当前的知识相反，对于“奶牛”数量较多的农场，氮的利用率更高。^-1 '，将其余N个输入保持恒定。较高的放养密度与较高的农业可持续性兼容。事实证明，由于减少了每头母牛的饲料N投入，添加的母牛产生的牛奶N的数量要多于每头单头母牛所产生的牛奶N的减少。奶牛使用氮的效率更高，从而提高了农场门的NUE和农场的可持续性。在本研究的数据集中，变量“奶牛ha ^-1 ”的相关性比以前的研究建议的要高：相关性是变量“化肥ha ^-1中的千克公斤kg ^-1 ”的1.4倍，后者是相关的1.5倍。 'kg精矿中的氮ha ^-1'。根据先前的知识，N个输入变量呈现负号。建议减少肥料，精矿和副产品中氮的输入以增加NUE。发现了意外的相互作用效应。