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IZVORNI I ZNANSTVENI ČLANCI – ORIGINAL SCIENTIFIC PAPERS Šumarski list br. 1–2, CXXXV (2011), 19-27 UDK 630* 114.2 (001) PEDOTRANSFER FUNCTIONS FOR BULK DENSITY ESTIMATION OF FOREST SOILS PEDOTRANSFER FUNKCIJE ZAPROCJENU GUSTOĆE ŠUMSKIH TALA 1 12 Milan KOBAL, Mihej URBANČIČ, Nenad POTOČIĆ , 31 Bruno DE VOS , Primož SIMONČIČ ABSTRACT: The data of 45 soil profiles from a 16 × 16 km grid across Slovenia was analysed to develop a local pedotransfer function (PTF) for bulk density (.b) estimation. In total, 106 soil horizons were considered. Concentration of organic carbon (OC) was found to be well correlated (r = -0.861, p < 0.001) with .b. Two separate line segments were fitted to the data, which was partitioned into two intervals, based on OC content (below 36.0 g/kg and above 36.0 g/kg). Nearly 80 % of the variability in .b is explained with segmented regression. The local PTF was compared with published PTFs and four validations indices (MPE, SDPE, RMSPE and R2) confirmed the highest prediction quality of the local PTF. The differences of carbon stock (Cpool) estimation, based on usage of different PTFs could be higher than 160 t OC per hectare. Prediction of carbon stocks could be substantially improved by calibration of the models coefficients with data stratified according to each unique soil type. Key words:pedotransfer function PTF, organic carbon OC, segmented regression, forest soil, carbon stock Cpool INTRODUCTION – Uvod Since forest soil sampling and analyses of chemical Nimmo,2003), while PTFs for estimation of soil bulk and physical properties of forest soils are time consu-density (.b)were introduced in the 1970s’ (e.g. Jeffrey, mingand labor intensive, the development of alternative 1970).At first, bulk density was correlated only with methods is indispensable. By using pedotransfer func-soil organic matter (SOM) (Adams,1973;Federer, tions (PTFs), soil scientists are able to get information 1993;RawlsandBrakensiek,1985,Honeysett on crucial soil properties, which are otherwise difficult andRatkowski,1989), but later the information on (expensive or time consuming) toobtain. PTFs can be soil texture was added to some PTFs (Leonavičiute, defined as statistical models for predicting soil physical 2000; Kauret al., 2002). Simple univariate models (bulk density, soil hydraulic properties, etc.) and chemi-were supplemented with multiple regressions and diffecal (e.g. cation exchange capacity) properties from other rent equations were developed separately for the organic more available and routinely measured properties. and the mineral soil layers(e.g. Harrisonin Bocock, 1981), or even for different genetic soil horizons The first PTF (for wilting coefficient) was develo (e.g.Leonavičiute,2000). Recently, various techni ped by Briggs and McLane 1907 (Landa and ques of tree regressions were incorporated in PTFs de 1 Mr. sc. Milan Kobal, Slovenian Forestry Institute, Večna pot 2, velopment (e.g.Martinetal., 2009). SI-1000 Ljubljana, milan.kobal@gozdis.si Mihej Urbančič, dipl. inž., Slovenian Forestry Institute, Soil bulk density (.b)is defined as the mass of a unit Večna pot 2, SI-1000 Ljubljana, mihej.urbancic@gozdis.si volume of dry soil (105 °C), which includes both solids Dr. sc. Primož Simončič, Slovenian Forestry Institute, and pores and, thus, bulk density reflects the total soil Večna pot 2, SI-1000 Ljubljana, primoz.simoncic@gozdis.si 3 2 porosity (FAO, 2006). Usually, it is expressed in g/cm Cvjetno naselje 41, HR-10450 Jastrebarsko, nenadp@sumins.hr Dr. sc. Nenad Potočić, Croatian Forest Research Institute, 3 or kg/dm. Soil bulk density is necessary for the asses 3 Mr. Bruno De Vos, Research Institute for Nature and Forest, sment of soil carbon and nutrient pools (Tamminen Gaverstraat 4, B-9500 Geraardsbergen, Belgium, bruno.devos@inbo.be andStarr,1994) and for other mass-to-volume conver |