performance evaluation of some internal pedotransfer functions to prediction soil moisture retention curve

soil moisture retention curve (smrc) is an important soil property which expresses reaction between matric potential and moisture of soil. direct measurement of soil matric potential and moisture is labour- and time-consuming. in order to prevail this problem, indirect methods are used for smrc prediction. pedotransfer functions (ptfs) are one of these indirect methods. this study was carried out to evaluate three internal pedotransfer functions, first and second models of ghorbani and homaee (1381) and sepaskhah and bondar (2002) derived in iran, to predict smrc in some iranian soils. also we tried to develop new different ptfs with better performance using the available information. therefore 42 soil samples with spatial distribution from northern region of iran, amol, babol and karaj were selected and divided in loam (20 samples) and clay loam (22 samples) texture classes. in evaluation of all existing ptfs, all 42 soil samples, and in developing new ptfs, 36 soil samples were used. the remaining six samples (three samples in each texture class) were used for validation of the new developed ptfs. in evaluation of the existing ptfs, results showed that the first and second models of ghorbani and homaee had alike and appropriate prediction of moisture in whole range of matric potential, whereas sepaskhah and bondar did not show an appropriate prediction. by the way, none of these ptfs had noticeable preference in specific texture classes in comparison with the others. new developed ptfs were highly significant (p<0.05). among the new developed models, improvement was evident in sepaskhah and bondar models.