A large gap between actual and potential herbage production of tall fescue is a major limitation for livestock production systems in Argentina. The objectives of this work were to (a) calibrate and test the ability of a published pasture–soil water model to represent herbage growth dynamics of tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] under different growing conditions, using data from controlled field experiments; (a) use the evaluated model to predict the magnitude and time of the year that N or soil water would constrain tall fescue from attaining its potential growth rate in the south-eastern Pampas of Argentina; and (c) quantify herbage production gains and temporal variability for a proposed improved management practice (IMP) of N fertilizer under different meteorological and soils scenarios. After tall fescue-specific calibration, the model accurately represented the response of tall fescue herbage mass to irrigation and N fertilization (root mean square error of prediction <550 kg DM ha⁻¹, R² > .70) observed in thirteen single-season, controlled, field experiments. Results from a 40-year simulation show that the gap between fertilized and unfertilized tall fescue pastures in Argentina can exceed 14 t DM ha⁻¹ year⁻¹. The proposed IMP maximized responses to N in autumn and early spring, reducing the annual herbage production gaps by 38%. The effect of IMP on annual herbage production was larger (4–5 t DM ha⁻¹ year⁻¹) than the effect due to variability in soils’ ability to store water (2–4 t DM ha⁻¹ year⁻¹) or annual variability in meteorological conditions (±1–2 t DM ha⁻¹ year⁻¹). This work provides a sound modelling approach to identify, for a particular forage species and site, most of the main gaps of herbage production; and to quantify, without the need of long-term, expensive field studies, some of the potential gains (and risks associated with temporal variability), that could be achieved by producers. In addition, our results clearly indicate that site-specific calibration is required for the model to provide accurate predictions and sound management advice to farmers.

中文翻译：

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阿根廷高羊茅草场的牧草产量差距分析：一种建模方法

高羊茅的实际和潜在牧草生产之间的巨大差距是阿根廷畜牧生产系统的主要限制。这项工作的目标是 (a) 校准和测试已发表的牧场-土壤水模型代表高羊茅 [黑麦草 (Lolium arundinaceum)] 的牧草生长动态的能力(Schreb.) Darbysh.] 在不同的生长条件下，使用来自受控田间实验的数据；(a) 使用评估模型预测氮或土壤水分在阿根廷东南部的潘帕斯草原中限制高羊茅达到其潜在增长率的幅度和时间；(c) 在不同的气象和土壤情景下，量化所提议的氮肥改进管理实践 (IMP) 的牧草产量增益和时间变异性。在高羊茅特定校准后，该模型准确地代表了高羊茅牧草质量对灌溉和施氮的响应（预测的均方根误差 <550 kg DM ha ^-1 , R ² > .70）在13个单季受控实地实验中观察到。40 年模拟的结果表明，阿根廷施肥和未施肥的高羊茅牧场之间的差距可超过 14 t DM ha ^-1 年^-1。拟议的 IMP 最大限度地提高了秋季和早春对 N 的响应，将年度牧草产量差距减少了 38%。IMP 对年度牧草产量的影响（4-5 t DM ha ^-1 年^-1）大于由于土壤储水能力的可变性（2-4 t DM ha ^-1 年^-1）或气象条件的年度变化（±1–2 t DM ha ^-1 年^-1）。这项工作提供了一种健全的建模方法，可以确定特定牧草种类和地点的大部分牧草生产差距；并在不需要长期、昂贵的实地研究的情况下量化生产者可以实现的一些潜在收益（以及与时间可变性相关的风险）。此外，我们的结果清楚地表明，模型需要特定地点的校准才能为农民提供准确的预测和合理的管理建议。