Improving the estimation of evaporation by the FAO-56 dual crop coefficient approach under subsurface drip irrigation
Improving the estimation of evaporation by the FAO-56 dual crop coefficient approach under subsurface drip irrigation
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DOI：
10.1016/j.agwat.2016.09.022
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发表时间：
2016-12
影响因子：
6.7
通讯作者：
V. Phogat;J. Šimůnek;M. Skewes;J. Cox;M. Mccarthy
中科院分区：
文献类型：
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作者：
V. Phogat;J. Šimůnek;M. Skewes;J. Cox;M. Mccarthy
蒸散的分配和估算灌溉对蒸发的贡献在管理稀缺水资源和帮助提高作物，特别是稀疏植被植物的水分生产力方面起着至关重要的作用。在本研究中，FAO-56双作物系数（DCC）估算作物条件下土壤蒸发量的方法适用于地下滴灌（SDI）。这种新方法涉及一个额外的变量，即灌溉深度对蒸发的贡献（fI,Es），该变量已被定义并纳入粮农组织-56用于估算蒸发层（0-15厘米）每日水分平衡的方程中。通过HYDRUS-2D模拟，评估了土壤质地、非均质性、灌溉深度、灌溉系统设计参数对fi、Es和土壤表面被灌溉浸湿的比例（fw）（以及暴露和浸湿的比例（few））的影响。将改进后的方法与现有的FAO-56方法在SDI条件下估算酿酒葡萄年产值成分进行了比较。模型模拟结果表明，在均匀、各向同性的轻纹理土壤中，当SDI放置在25 cm深度时，fi，Esfraction最小（0.04）。而在中、重质地土壤中，es1是轻质地土壤的4倍。细质地土的ph值（0.09）略高于中等质地土（0.07）。在具有两种不同质地层的双层土壤中，由于在滴漏线下方存在一层质地较重的土层，fw（0.12-0.16）较高。同样，在三层土壤（3个不同的质地层）中，将滴管放置在中间层可以有效地减少fi， esand fw0。在非均质土壤中，fw（0.18 ~ 0.30）和fi、Es（0.28 ~ 0.42）均显著增加。两个组分（fwandfI、Es）均随灌溉深度的增加而增加，但在壤土砂中fi、Es除外。当滴管放置在10厘米深度（蒸发区）时，分数略低于放置在土壤表面时的分数。使用相同的水量，不同的排放速率，对fi、沙子和fw馏分的影响不大。滴灌线间距的增加成比例地减少了土壤表面的湿润部分。使用现有的FAO-56程序估算的实地研究地点SDI灌溉酿酒葡萄的年蒸发量与使用改进程序相比被高估了约5-6%。然而，对于较重的土壤质地，两种方法之间的偏差增加了（18%）。因此，在估算地下滴灌下的蒸发量时，需要对现有的FAO-56程序进行调整。然而，在其他作物、土壤和气候条件下，需要进一步评估拟议的改良对蒸发的影响。
Partitioning of evapotranspiration and estimating of irrigation contribution to evaporation play a crucial role in managing scarce water resources and help in increasing the water productivity of crops, especially of sparsely vegetated plants. In this study, the FAO-56 dual crop coefficient (DCC) approach for estimating evaporation from soil under cropped conditions is adapted for subsurface drip irrigation (SDI). This new approach involves one additional variable, the fraction of the irrigation depth contributing to evaporation (fI,Es), which was defined and integrated into the FAO-56 equations for estimating daily water balance from the evaporation layer (0–15 cm). Impacts of soil texture, heterogeneity, irrigation depth, design parameters of the irrigation system onfI,Es, and the fraction of the soil surface wetted by irrigation (fw) (and consequently the exposed and wetted fraction (few)), were evaluated through HYDRUS-2D simulations. The modified procedure was compared with the existing FAO-56 method for estimating components of annualETfor wine grape under SDI.The model simulations showed that thefI,Esfraction in a homogeneous, isotropic light-textured soil was minimal (0.04) when SDI was placed at a depth of 25 cm. However, in medium and heavy textured soilsfI,Eswas 4 times larger than in light-textured soils. The value offwwas slightly higher in fine-textured (0.09) than in medium-textured soils (0.07). In Duplex soils with two contrasting textural layers,fw(0.12–0.16) was higher due to the presence of a heavy-textured soil layer just below the drip line. Similarly, in Triplex soils (3 different textural layers), placing the drip line in the middle layer effectively reduced bothfI,Esandfwclose to zero. In contrast,fw(0.18–0.30) andfI,Es(0.28–0.42) both increased considerably in heterogeneous soils. Both fractions (fwandfI,Es) increased with an increase in irrigation depths, except forfI,Esin loamy sand. The fractions were slightly lower when a drip line was placed at a depth of 10 cm (an evaporation zone) than when it was placed on the soil surface. Applying the same amount of water with different discharge rates had little impact onfI,Esandfwfractions. An increase in the drip line spacing proportionally decreased the wetted fraction on the soil surface. Annual evaporation for SDI irrigated wine grapes at the field study site, estimated using the existing FAO-56 procedure, was overestimated by about 5–6% compared to using the modified procedure. However, this deviation between the two approaches increased (18%) for heavier soil textures. It is concluded that the existing FAO-56 procedure needs to be adjusted when used to estimate evaporation under subsurface drip irrigation. However, the impact of the proposed modification on evaporation needs further evaluation under other crops, soils, and climatic conditions.