Statistical parameters of water retention equations of Iraqi soils

The power curve model log W = α + β Log ψ was employed to describe the functional relationship between water content (w) and soil mat ric potential ( ψ ) between + 1 and ++ 1500 kPa for 56 soils of different textural classes from the northern and central pans of Iraq. The model provided a good fit for all the reported data and Correlation coefficients were 0.99 in most cases. The model is examined and shown that the parameter β can be best estimated from clay content but it is poorly correlated with the parameter α. thus is possible to develop a procedure to determine soil moisture characteristic curves based on one paired value of potential and water content and a single mechanical property (clay content) . the sensitivity of of the model was assessed. It was found that the average error in estimating water content over the entire mat ric potential range did not exceed 2% . (author). 29 refs., 4 figs., 4 tabs