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Limitations of the Model Structure and Soil Hydraulic Property Observations in Pedotransfer Function Development
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  • Yunquan Wang,
  • Jieliang Zhou,
  • Rui Ma,
  • Gaofeng Zhu,
  • Yongyong Zhang
Yunquan Wang
China University of Geosciencessity

Corresponding Author:[email protected]

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Jieliang Zhou
China University of Geosciencessity
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Rui Ma
China University of Geosciences
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Gaofeng Zhu
Lanzhou University
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Yongyong Zhang
Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences
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The commonly applied pedotransfer functions (PTFs), which predict soil hydraulic properties (SHPs) from easily measured soil properties such as texture information, often account only for capillary forces. Recent advances in soil hydraulic modeling suggest that, to improve the prediction of SHPs under dry conditions, the impact of adsorption forces has to be taken into account. However, the lack of observations in particularly dry conditions, due to the difficult and time-consuming measurement, hinders the development of PTFs that predict SHPs from saturation to oven dryness. In this paper, we first present a simple method for predicting complete SHPs with limited measurements that cover only a relatively high matric potential range. With this method, we extended a public dataset to cover dry conditions, and then applied it to develop PTFs that can predict SHPs from saturation to oven dryness. This was achieved by applying the complete soil hydraulic model proposed by Wang et al. (2021), which accounts for both capillary and adsorptions forces and overcomes the unrealistic decrease near saturation for fine-textured soils. The impact of vapor diffusion was also considered. We further applied this method in extending an existing capillary-based PTF to dry conditions. The results showed that: 1) the proposed method performs very well in describing SHPs over the entire moisture range; 2) the PTFs developed with the extended observations and the complete model show a superior prediction performance, especially for the hydraulic conductivity; and 3) the extended capillary-based PTF improves the performance in describing SHPs under dry conditions.