Effect of Pasture Management System Change on In-Season Inorganic Nitrogen Pools and Heterotrophic Microbial Communities

Abstract

It has been assumed that the system of long-term pasture management exerts a significant impact on the soil microorganisms count, subsequently affecting the availability of mineral nitrogen (Nmin). This hypothesis was tested in a three-year experiment on a long-term pasture with two distinct systems of grass sward management, i.e., grazing and mowing. Mowing significantly increased the microorganisms count by 13%, 28%, 86%, and 2% for eubacteria (EU), actinobacteria (AC), molds (MO), and Azotobacter (AZ), respectively. The main reason was drought in 2006, which resulted in the domination of Dactylis glomerata L. in the grass sward, instead of Lolimum perenne L. and Poa pratensis L. The content of Nmin decreased through the vegetative growing season, reaching its lowest value after the 3rd grazing cycle. The impact of microorganisms on the Nmin pools increased in the order: molds < eubacteria < actinobacteria. The count of actinobacteria in the alkaline organic soil increased in response to drought, contribution of Dactylis glomerata L. in the sward, and the shortage of available phosphorus. The sound pasture management system is possible by introducing alternate grazing and mowing cycles. The core of sustainability is the enhanced activity of actinobacteria after changing the system from grazed into mowed.