Ritchie, J. T., A. Gerakis, and A. Suleiman. 1999. Simple model to estimate field-measured soil water limits. Transactions of the ASABE 42:1609-1614.
Engineering and modeling applications often require reasonable estimates of the upper and lower limits of plant extractable water. Laboratory measurements of these limits do not always coincide with field observations. Statistical models to estimate soil water retention can be complicated, and usually are not based on field measurements. The objective of this work was to develop simple, generic equations to estimate the field-measured limits of the soil water reservoir based on soil survey data such as texture and bulk density. We used linear regression to estimate the gravimetric upper limit from sand and clay content; the volumetric upper limit can be estimated from the gravimetric upper limit and bulk density. We used non-linear regression to estimate the volumetric plant extractable water from sand content. The lower limit can be estimated as the difference between the upper limit and the plant extractable water. We adjusted the predictions for coarse fragments and organic C and we placed reasonable upper and lower boundaries to our estimates. The equation for the drained upper limit has a RMSE of 0.030 kg kg–1 and uses two coefficients. The equation for the plant extractable water has a RMSE of 0.030 m3 m–3 and uses three coefficients. We tested the simple model with an independent data set. The RMSE of our model was similar or better than that of a more complex statistical model.
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