Testing Some Pedo-Transfer Functions (PTFs) in Apulia Region. Evaluation on the Basis of Soil Particle Size Distribution and Organic Matter Content for Estimating Field Capacity and Wilting Point

The knowledge of soil water retention vs. soil water matric potential is applied to study irrigation and drainage scheduling, soil water storage capacity (plant available water), solute movement, plant growth and water stress. To measure field capacity and wilting point is expensive, laborious and is time consuming, so, frequently, matemathic models, called pedo-transfer functions (PTFs) are utilized to estimate field capacity and wilting point through physical-chemical soil characteristics. Six PTFs have been evaluated (Gupta and Larson, 1979; Rawls et al., 1982; De Jong et al., 1983; Rawls and Brakensiek, 1985; Saxton et al., 1986; Vereecken et al., 1989) by comparing measured soil moisture values with estimated ones at soil water matric potential of -33 and -1500 kPa. Soil samples were collected (361) from 185 pedons of Apulian Region (Southern Italy). Accuracy of the soil moisture predictions is quantified with Root Mean Square Deviation (RMSD) between estimated and measured water retention values. In Apulia Region the tested PTFs give different results on soils grouped on the basis of textural composition and organic matter (O.M.) content both at the Field Capacity (FC) and Wilting Point (WP). At the FC, Gupta and Larson model has given the best performance in Clayey (C), Sandy clay loam (SaCL), Sandy loam (SaL) and Silty (Si) soil, in loamy and tendency silty soils with O.M. content less than 1.9% and in tendency sandy soils with O.M. content less than 1.5% and greater than 2%; the Rawls model in Silty clay (SiC) and Silty loam (SiL) soils, in tendency clayey soils with O.M. less than 2.3% and in loamy and tendency silty soils with O.M. greater than 1.9%; the Rawls and Brakensiek model in tendency sandy soils with O.M. content between 1.5 and 2%; the Saxton model in Silty clay loam (SiCL), Loamy sand (LSa) soils and in tendency clayey soils with O.M. content greater than 2.3% and the Vereecken model in Sandy clay (SaC), Loamy (L), Clay loam (CL) and Sandy (Sa) soils. At the WP, the Gupta and Larson model has resulted the best in SiL, Si soils and, in general, in loamy and tendency silty and in tendency sandy soils with O.M. content greater than 1.9% and 2%, respectively; the Rawls model in Loamy soils and in loamy and tendency silty soils with O.M. between 1.0 and 1.9%; the De Jong model in C soils; the Rawls and Brakensiek model in SiC, SaC, CL, SiCL, SaCL soils and generally in tendency clayey soils with whatever O.M. content and in tendency sandy soils with O.M. content between 0.8 and 2%; the Saxton model in loamy and tendency silty soils with O.M. content less than 1% and in tendency sandy soils with O.M. less than 0.8%; the Vereecken model in SaL, Sa and LSa soils.