Specific Surface Area and Multifractal Parameters of Associated Nitrogen Adsorption and Desorption Isotherms in Soils from Santa Catarina, Brazil

Nitrogen adsorption isotherms (NAI) and Nitrogen desorption isotherms (NDI) are commonly used to evaluate specific surface area (SSA) of soils and other materials. Scaling analysis of N-2 isotherms yield complementary information about the complexity of the soil surface. We evaluated the specific surface area (SSA) and examined the scaling properties of NAIs and associated NDIs from clayey soils, rich in organic matter sampled in Santa Catarina State, Brazil. Sixty six soil horizons were sampled in 13 profiles. Ten of these profiles were developed over volcanic rocks with a wide range of mineralogical composition. Clay content and cation exchange capacity (CEC) showed a weak positive correlation to SSA, which was attributed to variable clay mineralogy. Organic carbon content showed a weak negative correlation to SSA. Both NAIs and NDIs exhibited multifractal behavior, but its scaling properties were different so that adsorption isotherms showed higher scaling heterogeneity and were less evenly distributed measures than desorption isotherm. Also, parameterization by the Hurst exponent indicates NAIs were less persistent than NDIs. Differences in multifractality between NAIs and NDIs were attributed to contrasting physical processes during adsorption and desorption. Both, SSA and various multifractal parameters estimated from NAIs and NDIs differentiated between soils developed over either acid or basic parent material. Linear regression and principal component analysis (PCA) showed increasing carbon content decreased scaling heterogeneity and increased persistence of both, NAIs and NDIs. On the other hand, increasing clay content showed a trend to increase scaling heterogeneity and to decrease persistence during the adsorption and desorption phases.