Distribution of populations of micro-organisms in different aggregate size classes in soil as affected by long-term liming management

Abstract

This paper presents the results of experiments carried out at the Vezaiciai Branch of the Lithuanian Institute of Agriculture during the period 1996-2004. The effects of long-term liming (at 0.5 rate=3.8 t ha-1 CaCO3 every 7 years and 2.0 rate=15.0 t ha-1 CaCO3 every 3-4 years) on soil chemical properties, aggregate composition and population distribution of micro-organisms and activity of two enzymes across different size classes of soil aggregates (<0.25, 0.25-0.5, 0.5-1.0, 1.0-2.0, 2.0-3.0 and 3.0-5.0 mm) were investigated. The soil of the experimental site is a Dystric Albeluvisol and textural class is sandy loam (sand (2.0-0.05 mm) 51%; silt (0.05-0.002 mm) 34%; clay (<0.002 mm) 15%). Moderate periodical liming at0.5 rate every 7 years enabled us to maintain soil reaction at a low acidity level (pH in KCl 5.5), whereas when the soil was limed intensively at 2.0 rate every 3-4 years topsoil reaction was slightly alkaline: pH in KCl 7.2. Moderate liming (0.5 rate every 7 years) affects an increase in the amount of agronomically-valuable mesoaggregates (especially of 1.0-2.0 and 1.0-0.5 mm size class). Microbe distribution in different aggregate fractions in acid and moderately limed soil were not significantly different. In intensively limed soil, there was an observed tendency of microbe displacement from the smallest aggregate-size classes to the largest (1.0-2.0 mm).