Classification of Rendzina soils in Serbia according to the WRB system

Abstract

According to soil classification system used in Serbia (Škorić, Ćirić and Filipovski, 1985) Rendzina is a soil type within the order of automorphic soils and the class of humus-accumulative soils with an Amo-AmoC-C-R profile, which is developed on parent rock containing more than 20% of calcareous material. Rendzinas are divided onto subtypes - according to the parent material: (i) marl, marly limestone and soft limestone, (ii) loess and loess like sediments, (iii) dolomite sand, (iv) moraine; on varieties - according to stadium of evolution: (i) calcareous, (ii) decarbonated, (iii) brunified, (iv) colluvial, and forms - according to texture and coarse fragments content. Throughout the world, the term Rendzina (and Pararendzina) is used to denote soils formed on different calcareous parent material and it generally corresponds with Rendzic Leptosol of the WRB soil classification system. Rendzinas on marl, marly limestone and soft limestone is the most widespread subtype in Serbia, and the aim of this study was to precisely classify it according to the WRB 2015 system. Total of 29 Rendzina soil profiles from different parts of Serbia were studied. Field and laboratory investigations (soil depth, colour, coarse fragments, texture, structure, pH, soil organic carbon, base saturation) were determined using methods recommended by the WRB system (except for base saturation, where BaCl2, pH 8.1, was used instead of NH4OAc, pH 7). According to soil classification system used in Serbia, from total of 21 soil profiles on soft limestone, 16 were calcareous variety (form: 8 loamy, low or medium skeletal and 1 clay, medium skeletal); 13 decarbonated variety (loamy, low skeletal); and 2 colluvial variety (loamy, low skeletal); and 8 profiles on marl of which 7 were calcareous variety (loamy, low or medium skeletal), and 1 profile was decarbonated variety (loamy, low skeletal). According to WRB 2015 system, investigated Rendzinas were classificated to RSG of Leptosols (12 profiles), Regosols (10 profiles) and Phaeozems (7 profiles). Leptosols include Rendzinas with A-R soil profile, where continuous rock (10 profiles on soft limestone and 2 profiles on marl) starting ≤15-25 cm from the soil surface. For calcareous Rendzina variety, combinations of the principal qualifiers were: Rendzic, Rendzic Calcaric, and Skeletic Calcaric. The decarbonated variety matched the diagnostic criteria for the Eutric principal qualifier. The supplementary qualifiers for Leptosols were Loamic or Clayic, Aric and Humic. Renzinas deeper than 25 cm, usually with A-AC-R soil profile, having a mollic diagnostic horizon were classified to RSG of Phaeozems. For calcareous Rendzinas variety, combinations of the principal qualifiers were: Rendzic Calcaric or Rendzic Skeletic Calcaric. The decarbonated Rendzinas variety only matched criteria for the Leptic principal qualifier. Loamic and Aric supplementary qualifiers were added to Phaeozems. RSG of Regosols includes Rendzinas thicker than 25 cm, usually with A-AC-R soil profile, when surface horizon does not match diagnostic criteria of a mollic horizon (in slightly crushed samples a Munsell colour value of ≥3 moist, and ≤ 5 dry, and a chroma of ≥4 moist). Surface horizons were more than 20 cm deep (except for 2 profiles) and had over 0.6% (1.1-4.6%) soil organic carbon. For calcareous Rendzinas variety combinations of the principal qualifiers were: Leptic Calcaric or Leptic Skeletic Calcaric. For Colluvial Rendzinas variety (all calcareous) combination of the principal qualifiers was: Leptic Colluvic Calcaric. Loamic and Aric and/or Humic supplementary qualifiers were used for Regosols. Soil depth caused the first differentiation between Leptosols and Phaeozems, and soil (moist) colour caused the second differentiation between Phaeozems and Regosols. Somewhat brighter soil colour of Rendzina/Regosols is a result of low soil organic matter content and/or high content of calcaric material in the fine earth.