This is a four parameter function to determine water retention hydraulic parameters contained in a bimodal poresize distribution developed by Omuto. The parameters are for the first and second compartments
1  SSomuto(input, Ths1, alp1, Ths2, alp2)

input 
Suction potential/head as contained in the xcolumn of the xy water retention table or data 
Ths1 
This is saturated moisture content in the first compartment of a bimodal poresize distribution water retention characteristics 
alp1 
This is the inverse of airentry potential in the first compartment of a bimodal poresize distribution water retention characteristics 
Ths2 
This is saturated moisture content in the second compartment of a bimodal poresize distribution water retention characteristics 
alp2 
This is the inverse of airentry potential in the second compartment of a bimodal poresize distribution water retention characteristics 
Omuto model is a selfstarting biexponential model for nonlinear curve fitting model to water retention data. If warnings are given during the estimation process, try to increase the iteration limit using control function. Sometimes the warnings can be suppressed using (warn=1)/ignored since they do not terminate the process
A list of objects returned by standard R regression functions such as nls and lm
This function can also be used to fit water retention characteristics for a grouped dataset as well as with mixedeffects modelling
Christian Thine Omuto
Omuto CT. 2009. Biexponential model for water retention characteristics. Geoderma 149:235242
SSvgm, SSgard, SSfredlund
1 2 3 4 5 
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