Soil pore surface properties in managed grasslands

Properties of pore surfaces control adsorption and transport of water and chemicals in soils. Parameters are needed to recognize and monitor changes in pore surfaces caused by differences in soil management. Data on gas adsorption in soils can be compressed into parameters characterizing (a) area available to a particular adsorbate, and (b) surface roughness or irregularity. Our objectives were to see (a) whether models of adsorption on fractal surfaces 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 adsorption was measured in Gray Forest soil (Udic Argiboroll, Orthic Greyezem, clay loam) samples taken at four plots, where a long-term experiment on grassing arable land had been carried out for 12 years. The experiment had 2×2 design. Factors were ‘harvest–no-harvest’ and ‘fertilizer–no-fertilizer’. The hay was cut after over-seeding in harvested treatments every year. Ammonium nitrate, superphosphate, and potassium chloride were applied annually after the snowmelt to get the total amount of nutrients of 60 kg ha−1. The monolayer adsorption capacity was estimated from the Brunauer–Emmett–Teller model. A fractal Frenkel–Halsey–Hill model of adsorption on a fractal surface, and a thermodynamic adsorption model were applied in the range of relative pressures from 0.7 to 0.98 and provided good fit of data. Values of the surface fractal dimension Ds were in the range from 2.75 to 2.85. Removal of carbohydrates resulted in increase of Ds. Differences in management practices did not affect values of Ds in the scale range studied, whereas the monolayer capacity was affected. Both fertilization and harvesting resulted in an increase of the monolayer capacity, with the largest increase observed in soil that was fertilized but not harvested.