Chernozem humus state change of the Chelyabinsk region as an agricultural use result

The agricultural land monitoring program provides for monitoring the humus state of the studied lands, which is an integrated indicator of the natural soil fertility. The paper presents the results of studies on changes in the content of humus, total nitrogen, fractional-group composition of humus. According to analyzes carried out at the Chelyabinsk Research Institute of Agriculture, all subtypes of chernozem soils in the region showed a lower humus content on arable land compared to virgin analogs. Thus, the difference between virgin land and arable land in the first round was 1.02 % in leached chernozems, 2.16 % in ordinary and southern ones, 1.24 %, by the sixth round these differences were 3.5; 2.88 and 1.79 %, respectively. There was a slight increase in humus reserves in the virgin lands of leached and ordinary chernozem. The content of total nitrogen increased on virgin soil of leached chernozem by 39.5 %, ordinary chernozem by 45.4 %. In our opinion, this is due to the entry into the soil of a large amount of organic matter in the form of plant phytomass litter. An increase in the total nitrogen content on arable land is facilitated by climatic factors, as well as the release of post-harvest residues into the soil as a result of the application of the minimum technology for growing grain crops. The results of analyzes of the fractional-group composition of humus showed that in most types of soils, humic acids predominate in the composition of humus. In the southern chernozems, the content of fulvic acids is higher than that of humic ones. The data on optical density show that leached chernozems have a very high optical density, which indicates the predominance of mature humic acids in the humus composition. Fulvic acids prevail in the humic substances of southern carbonate chernozem, and the ratio of SGA:SFA. does not exceed 1. This type of soil has a lower optical density of humic acids.