Natalia Aleksandrovna Kulikova

The paper presents the results of the study of fatty acid profiles of typical chernozems with different management practice. The study showed that degradation of soil organic matter in typical chernozems is accompanied by depletion of fatty acids, while its accumulation resulted in an increase in their diversity. In this regard, the composition of fatty acid soil profiles allows classifying the soil successfully according to the prevailing processes of transformation of organic matter. An uneven distribution of fatty acids was discovered in soil aggregates of different sizes for the untillage chernozems, whereas arable chernozems possessed regular distribution of fatty acids among aggregates of different size. Eicosapentaenoic acid which is a moiety of microalgae, and dihomo-gamma-linolenic acid which is synthesized by fungi Mortierella can be considered as biomarkers of the withdrawal of typical chernozem from agricultural use to a fallow land.

In laboratory conditions, the decomposition of glyphosate with the formation of aminomethylphosphonic acid (AMPA) and its effect on the total abundance of bacteria and fungi, as well as the number of copies of genes encoding the enzymes C-P lyase of a-proteobacteria ( phnJ ), acid and alkaline phosphatase ( phoC and phoD ) and Fe-protein nitrogenase ( nifH ). It is shown that when applying glyphosate in recommended doses (5-10 mg/kg) 5-7% of the introduced herbicide is detected after 14 days, but when the dose is increased to 100 mg/kg, this value increases to 23%. Slowing down the rate of degradation of the herbicide appears only in the first week of incubation and is accompanied by a decrease in the number of copies of the phoC, phoD, nifH genes and an increase in the abundance of fungi. The obtained results indicate a predominant degradation of glyphosate with the C-P bond breaking and the formation of phosphates, as well as a possible inhibition of the nitrogen fixation process. It is shown that at an application dose of glyphosate 100 mg/kg, the accumulation of the first metabolite AMPA can occur during the degradation of the herbicide with a break in the C—N bond. Bioassay using wheat showed that when applying glyphosate at a dose of 100 mg/kg, there is an inhibition of plant development: the length of the roots and the biomass of the shoots reduced by 60 and 20% compared to the control, respectively. Based on the obtained data, it is proposed to use the reduction in the content of copies of the phoC gene and the growth of copies of ITS rRNA as indicators of the predominant decomposition of glyphosate through the sarcosin pathway. A reduction of copies of ITS rRNA gene by 40% or more can be used as an indicator of the possibility of AMPA accumulation during glyphosate degradation.

The historical and modern concepts of fallow lands (abandoned cropland), the causes of their occurrence and some features of their functioning are considered. The main stages of the development of abandoned cropland are highlighted from the perspective of a consistent change of vegetation in agrophytocenoses that arise after the cessation of soil cultivation. The literature data and existing approaches to assessing the land area of arable land withdrawn from agricultural circulation are analyzed. The prospects of using abandoned fallow lands both in the agricultural sector of agricultural production and in the broader ecosystem plan are considered. Attention is drawn to the fact that deposits of different ages are, in fact, chronological sequences of various dynamic biogeocenoses with actively transforming plant and soil components, which make it possible to assess, among other things, the rate of soil formation and degradation processes.