The nitrogen (N) fertilizer application rate (kg ha⁻¹ year⁻¹) in pastoral dairy systems affects the flow of N through the soil, plant and animal pools of the system. With better understanding of the magnitude of these pools and their fluxes, dairy systems could be managed to improve N use efficiency, therefore reducing losses to the environment. A study with three levels of N fertilizer, 0 (N0), 150 (N150) and 300 (N300) kg N ha⁻¹ year⁻¹, was conducted in the Canterbury region of New Zealand from 1 June 2017 till 31 May 2018. Farm measurements, e.g. pasture and milk production, were used to calibrate three different farm-scale models, DairyNZ’s Whole Farm Model, DairyMod, and Overseer^®. The models were used to extrapolate periodic farm measurements to predictions of carbon (C) and N pools and fluxes on an annual basis. Pasture and milk production per hectare increased from N0 to N300 by 70 and 58%, respectively. There was a concomitant increase in farm-gate N surplus (input–output) of 43%, resulting in predicted increases in N leaching and greenhouse gas emissions of 72 and 67%, respectively. By increasing N fertilizer from 0 to 300 kg N ha⁻¹ year⁻¹, 53% more feed N flowed through the dairy herd with surplus N deposited as urinary N increasing by 49%. Plant uptake and soil immobilization increased by 58 and 343%, respectively, but not enough to avoid substantial increases in leaching and emission losses. Carbon flux through the soil system increased through increased litter and faecal deposition, but with very little C sequestration because of accelerated microbial respiration rates.

中文翻译：

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使用不同氮肥制度的牧场奶牛生产系统中农场规模的碳和氮通量

牧场奶牛系统中的氮肥施用量（kg ha - ¹ 年^-1千克）会影响氮穿过系统土壤，植物和动物池的流量。通过更好地了解这些池的数量及其通量，可以管理乳制品系统以提高氮的利用效率，从而减少对环境的损失。自2017年6月1日至2018年5月31日，在新西兰的坎特伯雷地区进行了3种氮肥水平的研究，分别为0（N0），150（N150）和300（N300）kg N ha - ¹ 年- ¹年。农场测量，例如牧场和奶的生产，使用校准三种不同规模养殖场模型，DairyNZ的整个农场模型，DairyMod和巡察^®。该模型用于推断农场的定期测量数据，以预测碳（C）和氮库以及通量的年度变化。每公顷牧场和牛奶产量从N0分别增加到N300和70％。伴随而来的是农场大门的氮过剩（投入产出）增加了43％，从而导致氮的淋溶和温室气体排放预计分别增加了72％和67％。通过将氮肥从0公斤增加到300公斤N ha - ¹ 年^-1，流经奶牛群的饲料氮增加了53％，剩余的氮（尿氮）增加了49％。植物吸收和土壤固定化分别增加了58％和343％，但不足以避免淋溶和排放损失的大幅增加。通过增加凋落物和粪便的沉积物，通过土壤系统的碳通量有所增加，但是由于微生物呼吸速率的加快，碳的固存很少。