Pedotransfer Functions to Estimate Phosphate Maximum Adsorption Capacity for the B-Horizon of Soils from the State of Paraná, Brazil

Phosphorus is an important component in crop production in tropical areas. Phosphorus deficiency is highly common due to the high adsorption capacity of tropical soils rich in iron and aluminum oxi-hydroxides. Pedotransfer functions (PTF) can be defined as predictive functions of certain soil properties (phosphate adsorption) from other(s) more available, easily, routinely, or cheaply measured attributes. In the case of phosphurus, the maximum adsorption capacity (PMAC) is an important chemical attribute but determination usually takes several days. Soil samples taken from 307 different B-horizons covering an area of 200.000 km2, the whole state of Paraná-Brazil, were characterized in their basic chemical, physical and mineralogical attributes. Phosphorus maximum adsorption capacity (PMAC) was calculated for all samples using Langmuir isotherm and adsorption data. Several combinations of chemical, physical and mineralogical soil attributes presented correlation coefficient greater than 0.5 and might be used to calculate PMAC through PTFs. The best correlation (R2=0.78) was observed when clay (C) and sand (S) content, base saturation (V), cation exchange capacity (CEC), organic matter (OM), remaining P (Prem), iron extracted with ammonium acid oxalate (Feo) and hematite content (He) were used in the regression model: PMAC=711+8.47*C-5.09*S-1.62*V+8.35*CEC-2.95*OM-9.21*Prem+118.11*Feo-27.42*He. Pedotransfer functions available in the literature were compared to our model and most of them were unable to calculate the PMAC probably due to smaller range in the iron and aluminum oxides concentrations and distribution of iron oxides minerals observed.