DIGITALNA ARHIVA ŠUMARSKOG LISTA
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M. Kobal, M. Urbančič, N. Potočić, B. De Vos, P. Simončič: PEDOTRANSFER FUNCTIONS FOR BULK DENSITY ... Šumarski list br. 1–2, CXXXV (2011), 19-27 24 Figure 6 Performance of two local PTFs and published PTFs for the total dataset: estimated versus observed bulk densities with references to the 1:1 line. Slika 6. Kvaliteta predviđanja dvije lokalne i objavljenih pedotransfer funkcija za ukupni zbir podataka: procijenjene u odnosu na izmjerene gustoće s linijama izjednačenja. 3.3 Carbon stock calculation using different PTFs Izračun zalihe ugljika korištenjem različitih pedotransfer funkcija Carbon stock (C pool ) per hectare was calculated for different soil profiles, based on the usage of different PTFs (Table 4). Four different soil profiles were ran- domly selected from our soil databaseof the 16 × 16 km grid: Zajama, Lubnik, Besnica and Merljaki (Table 3). In the calculation of C pool , the stone content in soil hori- zons was considered, while the root portion was not.We assumednosurface rock outcrops. Soil profile “Zajama” was excavated in the Pokljuka plateau and is classified as Leptosol, soil profile “Lub- nik” was dug near Škofja Loka and is classified as Cam- bisol, profile “Besnica” was excavated near Ljubljana and is classified also as Cambisol, whereas soil profile “Merljaki” is classified asAcrisol and was excavated near Nova Gorica. Morphological, physical and chemi- cal properties are presented in detail inTable 3. The calculation of the C pool , based on the PTF of Kaur etal. (2002)gives highly underestimated values for all four soil profiles.The differences between cal- culated C pool using PTF SFI 6and measured C pool are not unambiguous, i.e. for soil profile “Lubnik” and “Be- snica” the carbon stock is underestimated, while for soil profile ‘’Zajama’’carbon stock is overestimated. The calculations of C pool revealed that differences of calculated carbon stock per hectare could be quite large and arestrongly dependent upon the PTFs algorithm. However, the lowest difference of the C pool based on measured and calculated bulk density was found for profile ‘’Merljaki’’. Both chemical and physical pro- perties of this profile are close to average soil proper- ties, included in this study, i.e. lower OC concentration and high bulk density (Figure 3). Consequently, the having the lowest value ofbias of the regression model (MPE), the lowest random variation of the predictions after correction for the global bias (SDPE),the lowest overall error of the predictions (RMSPE) and the hig- hest coefficient of determination (R2 ). In the case of high bulk density, local SFI 6 PTF seems slightly less accurate (Figure 6). Probably, that could be explained because of not including informa- tion onclay content, which is normally the highest just forthe soil horizons with high bulk densities (Urban- čič et al., 2005).For other PTFs the systematic error in predictions is evident from the scatterplots of Figure 6. |