In recent decades, the rate of milk production per unit land area and per cow has increased with the intensification of the dairy system. The possible environmental risks arising from nutrients surpluses, such as nitrogen (N), are often evaluated using the N balance approach. In Hokkaido, the biggest dairy farming area in Japan, many dairy farms have started introducing a new dairy farming system called the total mixed ration (TMR) and biogas system. Feed and manure are managed at a community scale in these systems while each farm focuses primarily on milking cows. Thus, calculating the N balance for this system is complicated. Therefore, this study aimed to evaluate the N surplus and use efficiency (NUE), focusing mainly on the community-based dairy farming system, as described above. We investigated twenty dairy farms comprising a TMR centre (TMR-based farms) and nineteen conventional dairy farms (conventional farms). The Hokkaido dairy farms had a smaller N surplus and higher NUE than farms in other countries. The whole farm N surplus and NUE ranged from −163 to 701 kg N ha⁻¹ and from 20% to 171% with median values of 40.5 kg N ha⁻¹ and 69.5%, respectively. One of the possible reasons for the smaller N surplus and higher NUE is a lower stocking rate (averaged 1.3 cows ha⁻¹) on Hokkaido dairy farms. There were strong relationships between feed N and N surplus because the studied dairy farms depended on purchased feed. In the comparison between the TMR centre and conventional dairy farms, the milk production level per cow and stocking rate tended to increase, and variations between farms decreased on the TMR-based farms. Increasing the amount of home-grown feed with pasture management is essential to decreasing N surplus for the new dairy farming systems.

近几十年来，随着奶业系统的集约化，单位土地面积和每头奶牛的产奶率不断提高。通常使用 N 平衡方法评估由氮 (N) 等营养物质过剩引起的可能环境风险。在日本最大的奶牛养殖区北海道，许多奶牛场已经开始引入一种新的奶牛养殖系统，称为全混合日粮（TMR）和沼气系统。在这些系统中，饲料和粪便在社区范围内进行管理，而每个农场主要专注于挤奶。因此，计算该系统的 N 余额很复杂。因此，本研究旨在评估氮过剩和利用效率（NUE），主要关注基于社区的奶牛养殖系统，如上所述。我们调查了 20 个奶牛场，包括一个 TMR 中心（基于 TMR 的农场）和 19 个传统奶牛场（传统农场）。与其他国家的奶牛场相比，北海道奶牛场的氮盈余较小，NUE 较高。整个农场的氮盈余和 NUE 范围为 -163 至 701 kg N ha^-1和从 20% 到 171%，中值分别为 40.5 kg N ha ^-1和 69.5%。N 盈余较小和 NUE 较高的可能原因之一是北海道奶牛场的放养率较低（平均 1.3 头奶牛 ha ^-1）。由于所研究的奶牛场依赖于购买的饲料，因此饲料 N 和 N 过剩之间存在密切关系。在TMR中心与传统奶牛场的比较中，每头奶牛的产奶量和存栏率有增加的趋势，而在TMR基地的农场中，农场之间的差异减少。通过牧场管理增加自产饲料的数量对于减少新奶牛养殖系统的氮过剩至关重要。