Solonetz microbiocenosis as an indicator of environmental change when replacing forage crop rotations with sown meadow

Abstract

In the Baraba Plain, the influence of crop rotations with sweet clover and awnless bromegrass on solonets has been studied in dynamics for more than 30 years. It has been noted that in the soil with phytomeliorative crop rotations total salt reserves have significantly decreased in comparison with the initial virgin soil. In the 0–20 cm soil layer, their number decreased 3.8–4.4 times, in the 20–40 cm layer – 4.6–7.7 times. As a result of grassing of the phytomeliorative crop rotation plots with a mixture of awnless bromegrass and alfalfa blue-hybrid, the effect of desalinization is decreasing (in the upper layer on average by 6.4 and 9.3%, in the lower layer – by 24.9% in the aftermath of the crop rotation with awnless bromegrass). The identified changes in the soil salinity have been reflected in the representation of salt-tolerant and salt-sensitive bacteria. The abundance of low salt-tolerant representatives of the class Spartobacteria on the grassed area after crop rotations with sweet clover and bromegrass decreased by 3.2 and 3.6 times, and the abundance of the relatively salt-loving Cytophagia increased by 1.6 and 2.4 times. In the sown meadow after crop rotation with sweet clover, a higher amount of complexly decomposable plant residues (mainly cereals) was observed, as evidenced by the increased content of acidobacteria. According to the abundance of the genera Gaiella from the class Thermoleophilia and Microlunatus from the class Actinobacteria, the meliorative effect in terms of desalinization and aeration of solonets is greater in sweet clover than in bromegrass. Grassing increases mineralization activity and oligotrophic soil in solonetz on average in 20–40 cm layer more strongly than in 0–20 cm layer by 1.6–2.2 times. Potential microbiological humus accumulation under sown meadow decreases in the upper layer of the plot previously occupied by the rotation with sweet clover, and in the lower layer – by the rotation with bromegrass.