Superficie específica y parámetros multifractales obtenidos a partir de isotermas de adsorción y desorción de suelos de la región serrana del sur de Brasil

Abstract

Nitrogen adsorption isotherms (NAI's) and Nitrogen desorption isotherms (NDI's) are commonly used to evaluate specific surface area (SSA) and microporosity of soils and other materials. Scaling analysis of N2 isotherms may yield cemplementary infermatien abeut the complexity ef the soil surface. Eleven soil profiles, representative of the mountain region of Santa Catarina State, 8razil, were georeferenced, sampled, morphologically described, and classified. Nine of the sampled soil pretiles were develeped over velcanic recks with a wide range ef mineralegical compesitien. Six different horizons were sampled for each ef the studied pretiles. General soil physical chemical and mineralogical properties were analyzed. Aggregate soil samples ef the aggregate 11 profiles also were cellected and this aggregates were used to determine both NAis and associated NDis isotherms. Data gathered frem NAis and NDis were used te asses the specific surface area (SSA) and to examined the scaling properties using multifractal analysis. The studied seils were rich in organic matter and in general also exhibited high clay contents. The specific surface area values were relatively high, but showed a range of variation among the studied soil profiles and between successive horizons of the same profile. The microporosity also showed wide differences, which were important for understanding the mevement and retention of water in them. Clay content and cation exchange capacity (CEC) showed a positive correlation to SSA, which was attributed to variable clay mineralogy. Organic carbon content showed a weak negative correlation to SSA. 8oth NAis and NDis exhibited multifractal behavior, but its scaling properties were different so that adsorption isotherms showed higher scating heterogeneity and were tess evenly distributed measures than desorption isotherm. Differences in multifractality between NAI's and NDI's were attributed to centrasting physical processes during adsorption and desorption. 8oth, SSA and various multifractal parameters estimated from NAI's and NDI's differentiated between soits 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, NAI's and NDI's. On the other hand, increasing clay content showed a trend to increase scaling heterogeneity and to decrease persistence during the absorption and desorption phases.