Extrapolative Capability of Two Models That Estimating Soil Water Retention Curve between Saturation and Oven Dryness

<div><p>Accurate estimation of soil water retention curve (SWRC) at the dry region is required to describe the relation between soil water content and matric suction from saturation to oven dryness. In this study, the extrapolative capability of two models for predicting the complete SWRC from limited ranges of soil water retention data was evaluated. When the model parameters were obtained from SWRC data in the 0–1500 kPa range, the FX model (Fredlund and Xing, 1994) estimations agreed well with measurements from saturation to oven dryness with RMSEs less than 0.01. The GG model (Groenevelt and Grant, 2004) produced larger errors at the dry region, with significantly larger RMSEs and MEs than the FX model. Further evaluations indicated that when SWRC measurements in the 0–100 kPa suction range was applied for model establishment, the FX model was capable of producing acceptable SWRCs across the entire water content range. For a higher accuracy, the FX model requires soil water retention data at least in the 0- to 300-kPa range to extend the SWRC to oven dryness. Comparing with the Khlosi et al. (2006) model, which requires measurements in the 0–500 kPa range to reproduce the complete SWRCs, the FX model has the advantage of requiring less SWRC measurements. Thus the FX modeling approach has the potential to eliminate the processes for measuring soil water retention in the dry range.</p></div

Mean error (ME) and root mean square error (RMSE) of the FX model (Fredlund and Xing, 1994) for the tested eight soils from saturation to oven dryness: FX-1 and FX-3 indicate that the parameters were obtained by fitting the models to the measurements in the suction range of 0 to 100 kPa and 0 to 300 kPa, respectively.

<p>Mean error (ME) and root mean square error (RMSE) of the FX model (Fredlund and Xing, 1994) for the tested eight soils from saturation to oven dryness: FX-1 and FX-3 indicate that the parameters were obtained by fitting the models to the measurements in the suction range of 0 to 100 kPa and 0 to 300 kPa, respectively.</p

Soil organic matter content (OM) and texture of the soils.

<p>Soils 1-7 were collected in China and soil 8 was collected in the USA.</p><p>Soil organic matter content (OM) and texture of the soils.</p

Comparison of measured and estimated soil water retention curves from the FX model (Fredlund and Xing, 1994) and the GG model (Groenevelt and Grant, 2004).

<p>The model parameters were obtained by fitting the models to the measurements in the suction range of 0 to 1500 kPa.</p

Texture of the soils from Campbell and Shiozawa (1992) and Prebble (1991).

<p>Texture of the soils from Campbell and Shiozawa (1992) and Prebble (1991).</p

Comparison of measured and estimated soil water retention curves from oven-dryness to saturation from the FX model (Fredlund and Xing, 1994) and KCGS model (Khlosi et al., 2006) on 10 soils from Prebble (1991).

<p>FX-1 and KCGS-1 indicate that the parameters were obtained by fitting the FX model and KCGS model to the measurements in the suction range of 0 to 100 kPa, respectively.</p

Comparison of measured and estimated soil water retention curves from oven-dryness to saturation from the FX model (Fredlund and Xing, 1994) on 10 soils from Prebble (1991).

<p>FX-1 and FX-3 indicate that the parameters were obtained by fitting the models to the measurements in the suction range of 0 to 100 kPa and 0 to 300 kPa, respectively.</p

Mean error (ME) and root mean square error (RMSE) of the FX model (Fredlund and Xing, 1994) and the GG model (Groenevelt and Grant, 2004) for the tested soils from saturation to oven dryness.

<p>Soil water retention data in the 0–1500 kPa suction range were used for model establishment.</p><p>Mean error (ME) and root mean square error (RMSE) of the FX model (Fredlund and Xing, 1994) and the GG model (Groenevelt and Grant, 2004) for the tested soils from saturation to oven dryness.</p

Comparison of measured and estimated soil water retention curves from oven-dryness to saturation from the FX model (Fredlund and Xing, 1994) on six soils measured by Campbell and Shiozawa (1992).

<p>FX-1 and FX-3 indicate that the parameters were obtained by fitting the models to the measurements in the suction range of 0 to 100 kPa and 0 to 300 kPa, respectively.</p

Mean error (ME) and root mean square error (RMSE) of the FX model (Fredlund and Xing, 1994) and KCGS model (Khlosi et al., 2006) for the tested 16 soils from Campbell and Shiozawa (1992) and Prebble (1991) from saturation to oven dryness: FX-1 and KCGS-1 indicate that the parameters were obtained by fitting the FX model and KCGS model to the measurements in the suction range of 0 to 100 kPa, respectively.

<p>FX-3 indicates that the parameters were obtained by fitting the FX model to the measurements in the suction range of 0 to 300 kPa.</p><p>Mean error (ME) and root mean square error (RMSE) of the FX model (Fredlund and Xing, 1994) and KCGS model (Khlosi et al., 2006) for the tested 16 soils from Campbell and Shiozawa (1992) and Prebble (1991) from saturation to oven dryness: FX-1 and KCGS-1 indicate that the parameters were obtained by fitting the FX model and KCGS model to the measurements in the suction range of 0 to 100 kPa, respectively.</p