Soil pore surface properties in managed grasslands

Properties of pore surfaces control adsorption and transport of water and c hemicals in soils. Parameters are needed to recognize and monitor changes i n pore surfaces caused by differences in soil management. Data on gas adsor ption in soils can be compressed into parameters characterizing (a) area av ailable to a particular adsorbate, and (b) surface roughness or irregularit y. Our objectives were to see (a) whether models of adsorption on fractal s urfaces are applicable to water vapor adsorption in soils in the capillary condensation range, and (b) whether differences in long-term management of grasslands are reflected by soil pore surface properties. Water vapor adsor ption was measured in Gray Forest soil (Udic Argiboroll, Orthic Greyezem, c lay loam) samples taken at four plots, where a long-term experiment on gras sing arable land had been carried out for 12 years. The experiment had 2x2 design. Factors were 'harvest-no-harvest' and 'fertilizer-no-fertilizer', T he hay was cut after over-seeding in harvested treatments every year. Ammon ium nitrate, superphosphate, and potassium chloride were applied annually a fter the snowmelt to get the total amount of nutrients of 60 kg ha(-1). The monolayer adsorption capacity was estimated from the Braunauer-Emmett-Tell er model. A fractal Frenkel-Halsey-Hill model of adsorption on a fractal su rface, and a thermodynamic adsorption model were applied in the range of re lative pressures from 0.7 to 0.98 and provided good fit of data. Values of the surface fractal dimension D-s were in the range from 2.75 to 2.85. Remo val of carbohydrates resulted in increase of D-s. Differences in management practices did not affect values of D-s in the scale range studied, whereas the monolayer capacity was affected. Both fertilization and harvesting res ulted in an increase of the monolayer capacity, with the largest increase o bserved in soil that was fertilized but not harvested. (C) 2000 Elsevier Sc ience B.V. All rights reserved.