Stabilization of aggregates by the microbial biomass as affected by soil texture and type

Abstract

The microbial biomass is an important factor in rendering aggregates more resistant to slaking. The aim of the present work was to characterize the short-term influence of microbial biomass on the water stability of aggregates (1–2 mm) in different soils. The first part of the study focused on the temporal relationship between biomass production and aggregate stabilization after substrate amendment. Rewetted aggregates of three soils, differing in their physico-chemical properties, were amended with glucose (400 mg 100 g −1 soil) and nitrogen (6.7 mg 100 g −1 soil) and incubated for 18 days at 20°C. The results confirmed the importance of a readily available C-source for the rapid stabilization of aggregates by soil microorganisms. In the second part, the stabilization of aggregates induced by the addition of glucose and nitrogen (dosage as above) in a 7 day incubation experiment at 20°C was studied in a range of 35 soils. The soils belonged to different textural classes (sands, loams, clays) and to different typological units. The stability increase produced by the microbial biomass was greatest in the sandy soils (< 15% clay) and least in the clays (> 35% clay), resulting in an equalizing of the stability in the two texture groups at the end of the incubation. The findings indicate that there is a potential for microbial stabilization in soils of different textural composition; however, the microbial influence is most pronounced in sandy soils. In the soil typological units of Dystric Gleysols, Calcic Chernozems, Gleyic Chernozems, Dystric Cambisols and Planosols, glucose and nitrogen led to a significant increase in the stability of aggregates, but to a different extent. The smallest increase was found in the Gleyic Chernozems, which had the highest content of organic matter and initial biomass.