Farm-gate balances for nitrogen (N) and phosphorus (P) were used to determine the potential nutrient surplus and nutrient-use efficiency of three grassland-based milk production systems. These were either full-time grazing (FG) or part-time grazing with indoor feeding of fresh herbage with low (IF) or substantial concentrate allowance (IFplus). Data collected over 3 years were used (a) from 3 × 8 commercial dairy farms, and (b) from a controlled experiment. On FG, IF and IFplus farms, the N surplus (net input minus net output) was 78.6, 75.1 and 138.2 kg N ha^− 1 a^− 1, respectively, and N use efficiency (NUE; net output/net input) was 0.33, 0.44 and 0.34, respectively. Annual P inputs and outputs were relatively balanced, with a higher P use efficiency (PUE) found for FG (1.19) and IF (0.97) farms than for IFplus farms (0.57). The most important input sources, apart from biological N₂ fixation and atmospheric N deposition, were mineral fertilizer N, concentrate N/P in IFplus, and animal manure P. Results from the controlled experiment confirmed most of these findings. In general, the IF provided an efficient nutrient use at a relatively low surplus. Accounting for off-farm losses associated with feed inputs and manure export reduced the system NUE and PUE substantially. The large variability in nutrient-use efficiency among the commercial farms indicates a clear potential for improvement. The average N surplus could be reduced by approximately 40% in reference to the best performing farms in each system.

中文翻译：

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草原和牧场奶生产系统中农场门口的养分平衡，其中包括全日制或非全日制放牧和新鲜草场室内饲喂，浓度不同

氮（N）和磷（P）的农场门平衡被用来确定三种基于草原的牛奶生产系统的潜在养分过剩和养分利用效率。这些是全日制放牧（FG）或非全日制放牧，室内饲喂低（IF）或大量浓缩物（IFplus）的新鲜牧草。使用（a）3×8商业奶牛场和（b）对照实验收集了3年以上的数据。在FG，IF和IFplus农场，N盈余（净投入减去净产出）分别为78.6、75.1和138.2 kg N ha ^-1 a ^-1，氮的使用效率（NUE；净输出/净输入）分别为0.33、0.44和0.34。年度磷的投入和产出相对平衡，FG（1.19）和IF（0.97）农场的磷利用效率（PUE）比IFplus农场（0.57）高。除生物N ₂以外，最重要的输入源固定和大气中的氮沉降包括矿物肥料氮，IFplus中的精氮/磷和动物粪便P。对照实验的结果证实了其中的大多数发现。通常，中频可在相对较低的剩余量下提供有效的养分利用。考虑到与饲料投入和粪便出口相关的农场外损失，大大减少了系统NUE和PUE。商业农场中养分利用效率的巨大差异表明有明显的改进潜力。相对于每个系统中表现最好的农场，平均氮过剩可以减少约40％。