Gesamtporenvolumen und Porengrößenverteilung in unbearbeiteten und bearbeiteten Lößböden

Abstract

Total porosity and pore size distribution in untilled and tilled loess soils.Soil core samples were taken from untilled and tilled soils of a no‐tillage experiment to determine total porosity and pore size distribution. The soil samples were collected at short time intervals during 1969–1971 from 2–6 cm depth of a Grey Brown Podzolic Soil (Typudalf) deriverd from loess.1. Total porosity differed in untilled and tilled plots on the average by 4.7 vol.% (table 2). The seasonal changes are more pronounced on the tilled soil. Higher values of total porosity are observed during spring and fall, as compared to summer. Values are influenced by soil cultivation, rainfall and green manure crops (fig. 1a, b).2. The changes of the fraction of large pores (> 30 μ), expressed on a volume basis, are similar to the changes in total porosity in direction but greater in extent. On the contrary the seasonal changes of the fractions of medium pores (3–30 μ), small pores (0,2–3,0 μ) and very small pores (< 0, 2 μ) appear to be independent from changes in total porosity (fig. la, b).3. Fig. 2, showing the relation between total porosity and pore size distribution, may induce the wrong impression, that a decrease in total porosity results in an increase of the quantity of small and very small pores, accompanied with an excessive reduction of the quantity of large pores. If this relation is based on weight (100 g of solid soil particles) and not on volume (100 cm3 of soil particles and pores), it becomes clear, that compacting and loosening the soil investigated affect mainly the amount of large pores.4. The seasonal changes of soil water content in the field influence pore size distribution. Under the condition of constant total porosity increasing water content at sampling date induces a pore size redistribution in favour of the pores > 300 μ and 1,5–3,0 μ (table 3).5. A decrease in total porosity does not induce an increase in the homogeneity of the soil investigated (fig. 3).6. The average total porosity of the untilled and tilled soil is near the lower and upper limit respectively of the range, which is considered to be the optimum for air capacity.