Structural aggregates size influence on the microbial biomass content under different land use

Abstract

The main purpose of this research was to establish the relationship between microbial biomass content and the soil structural aggregates size in the leached chernozem from Moldova. For research was chosen three experimental plots in three different lands management systems. From this point of view was studied leached chernozem under 60 year-old fallow in the forest strip from the field edge (forest strip), the long-term arable chernozem with crop rotation without green fertilizers (conventional agriculture) and the long-term arable chernozem covered for nine years with cover crops (grass mixture of Ryegrass and Lucerne). The studies have shown that the microbial biomass content in soil aggregates decrease in the sequence: 60 year-old fallow land → arable land under ryegrass → arable land. The largest amount of microorganisms in the soil under fallow leached chernozem is concentrated in soil particles with a smaller size – 0.5- 0.25 mm and < 0.25 mm. As a result, resistance of natural soil matrix to natural and anthropogenic negative impacts is higher than in the soils from agricultural ecosystems. The microbial biomass in arable chernozem is lower by 2.9-3.0 times than in the fallow chernozem. The microorganisms’ distribution in the arable chernozem has more or less uniform character. The soil structure destruction and the significant deterioration of microorganisms in arable chernozems aggregates lead to their natural stability decrease and to the degradation processes development. The use of ryegrass for the long-term arable chernozem quality restoration contributed to the microbes’ content increase in the soil aggregates with 14.4-15.1% but these values do not achieve the level of the soil under fallow.