Volatilization of NH3 following urea application or livestock urine deposition can result in significant loss of N to the environment. Urea hydrolysis to NH4 + results in an increase in pH, which in turn promotes transformation of NH4 + to NH3 . Accurately predicting changes in soil pH following urea (or urine) application will allow successful simulation of NH3 volatilization. The magnitude of the pH change depends on the soil's pH buffering capacity (pHBC). However, as actual pHBC values are not generally available, pHBC proxies (e.g., cation exchange capacity) have been used in modeling studies. In a 34-d laboratory incubation study, we measured soil pH and mineral N (NH4 + and NO3 - ) following a large application of urea (800 mg N kg-1 soil) to four soils with a range of pHBC values. In a second incubation, pH changes and mineral N dynamics were monitored in soil treated with sheep urine (773 mg N kg-1 soil) in the absence and presence of the nitrification inhibitor dicyandiamide. In both incubations, pH changes associated with urea hydrolysis and subsequent nitrification of NH4 + were predicted well using measured pHBC data. Our results confirmed that pHBC is base-type dependent (values greater when measured using KOH than NH4 OH). Soil pHBC is easily measured, and the use of a measured value (determined using NH4 OH) can improve model simulations of pH in the field and, potentially, lead to improved estimates of NH3 loss from animal-deposited urine patches and urea-treated soil.

中文翻译：

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响应尿素和羊尿的应用预测土壤 pH 值变化

施用尿素或牲畜尿液沉积后 NH3 的挥发会导致 N 大量流失到环境中。尿素水解为 NH4+ 导致 pH 值升高，进而促进 NH4+ 向 NH3 的转化。准确预测尿素（或尿液）施用后土壤 pH 值的变化将允许成功模拟 NH3 挥发。pH 变化的幅度取决于土壤的 pH 缓冲能力 (pHBC)。然而，由于实际的 pHBC 值通常无法获得，因此 pHBC 代理（例如，阳离子交换容量）已被用于建模研究。在一项为期 34 天的实验室孵化研究中，我们在将尿素（800 mg N kg-1 土壤）大量施用到具有一系列 pHBC 值的四种土壤后测量了土壤 pH 值和矿物质 N（NH4 + 和 NO3 - ）。在第二次孵化中，在硝化抑制剂双氰胺不存在和存在的情况下，在用羊尿（773 mg N kg-1 土壤）处理的土壤中监测 pH 值变化和矿物质氮动态。在这两种培养中，使用测量的 pHBC 数据很好地预测了与尿素水解和随后的 NH4+ 硝化相关的 pH 变化。我们的结果证实 pHBC 依赖于碱类型（使用 KOH 测量时的值大于 NH4 OH）。土壤 pHBC 很容易测量，并且使用测量值（使用 NH4 OH 确定）可以改进现场 pH 值的模型模拟，并有可能改进对动物沉积的尿液斑块和尿素处理土壤中 NH3 损失的估计. 使用测量的 pHBC 数据可以很好地预测与尿素水解和随后的 NH4+ 硝化相关的 pH 变化。我们的结果证实 pHBC 依赖于碱类型（使用 KOH 测量时的值大于 NH4 OH）。土壤 pHBC 很容易测量，并且使用测量值（使用 NH4 OH 确定）可以改进现场 pH 值的模型模拟，并有可能改进对动物沉积的尿液斑块和尿素处理土壤中 NH3 损失的估计. 使用测量的 pHBC 数据可以很好地预测与尿素水解和随后的 NH4+ 硝化相关的 pH 变化。我们的结果证实 pHBC 依赖于碱类型（使用 KOH 测量时的值大于 NH4 OH）。土壤 pHBC 很容易测量，使用测量值（使用 NH4 OH 确定）可以改进现场 pH 值的模型模拟，并有可能改进对动物沉积的尿液斑块和尿素处理土壤中 NH3 损失的估计.