Surface soil water dynamics in pastures in northern New South Wales. 3. Evapotranspiration
Surface soil water dynamics in pastures in northern New South Wales. 3. Evapotranspiration
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新南威尔士州北部牧场的表层土壤水动态。
DOI：
10.1071/ea03041
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发表时间：
2004
影响因子：
1.4
通讯作者：
S. Harden
中科院分区：
文献类型：
--
作者：
S. R. Murphy;G. Lodge;S. Harden
蒸散是新南威尔士州西北坡放牧牧场水文平衡的主要组成部分，占年降雨量的93%。然而，近80%的蒸散可能发生在裸露的土壤蒸发中，这意味着植物生长所需的水不可用。很少有研究报告牧场的实际蒸散量，特别是在新南威尔士州北部。这里报道的研究是为了使用蒸发穹顶技术测量实际的蒸散量，适用于一系列牧场、凋落物和地面覆盖的地块。在2000年秋季和2001年秋季之间的每个季节都进行了测量，包括湿土壤表面条件和干土壤表面条件，以记录可能预期的数值范围。在天然牧场地区也进行了类似的测量，以量化放牧条件下的值。还量化了与每次蒸散测量相关的一系列其他变量；这些变量包括净辐射能量的组成部分、大气条件、牧场物理特征、地面覆盖和土壤水分含量。这些数据被用来确定最重要的变量，这些变量可能受到放牧管理的影响或与放牧管理相互作用，这些变量解释了日蒸散量的变化。冬季至夏季的小时蒸散量为0.02~0.82 mm/h，日蒸散量为0.2~7.6 mm/d。包括太阳辐射、牧草质量、水汽压差和土壤水分等变量的线性回归模型可解释高达93%的日蒸散量变化。这些模型预测，高凋落物质量(3000千克干物质/公顷)可使湿润土壤的蒸发量减少多达1毫米/天，从而对年度水文平衡做出重大贡献。利用可持续放牧系统牧场模型对放牧草地的模拟研究表明，放牧管理可能会影响林冠、枯枝落叶层和裸地的蒸腾和蒸发分配。轮牧的土壤蒸发量低于连续放牧，蒸腾和冠层蒸发高于连续放牧。因此，牧场在夏季和冬季可能需要不同的管理，以便将裸露的土壤蒸发和树冠截留损失降至最低，以最大限度地利用可供牧场使用的储存土壤水分。蒸发损失较低的牧场可能具有更高的生产力和可持续性。
Evapotranspiration is the major component of the hydrological balance of grazed pastures on the North-West Slopes of New South Wales, representing up to 93% of annual rainfall. Nearly 80% of evapotranspiration may occur as bare soil evaporation, however, representing water not available for plant growth. Few studies have reported daily values of actual evapotranspiration for pastures, particularly in northern New South Wales. The studies reported here were conducted to measure actual evapotranspiration using an evaporation dome technique, for plots with a range of pasture, litter and ground cover. Measurements were taken in each season between autumn 2000 and autumn 2001, with both wet and dry soil surface conditions, to document the range of values that might be expected. Similar measurements were conducted in areas of natural pasture, to quantify values under grazed conditions. A range of other variables were also quantified in association with each evapotranspiration measurement; these included components of net radiant energy, atmospheric conditions, pasture physical characteristics, ground cover and soil water content. These data were used to identify the most important variables, which may be influenced by or interact with grazing management, that account for variation in daily evapotranspiration values. Hourly evapotranspiration ranged from 0.02 to 0.82 mm/h and daily values ranged from 0.2 to 7.6 mm/day, in winter to summer, respectively. Linear regression models that included variables of solar radiation, herbage mass, vapour pressure deficit and soil water content accounted for up to 93% of the variation in daily evapotranspiration values. These models predicted that high litter mass (3000 kg DM/ha) may reduce evaporation by up to 1 mm/day for wet soils, making a substantial contribution to the annual hydrological balance. A simulation study of a grazed pasture, using the Sustainable Grazing Systems Pasture Model, indicated that grazing management may influence the partitioning of transpiration and evaporation from canopy, litter and bare soil. With rotational grazing, predicted soil evaporation was lower and transpiration and canopy evaporation were higher than with continuous grazing. Hence, pastures may require different management between summer and winter, so that bare soil evaporation and canopy interception losses are minimised, to maximise stored soil water available for pasture use. Pastures with lower evaporative losses are likely to have higher productivity and sustainability.