The research is based on the results of local monitoring in 1990-2018 on reference plots of agricultural lands and archival materials of a large-scale agrochemical survey. The purpose of the research is to identify patterns of change in the humus content of arable soils of the forest-steppe in the Omsk region after prolonged use in agriculture. The objects of research were the soils of the forest-steppe zone of the Omsk Region: ordinary chernozem low-power low-humus heavy loamy soil; meadow-chernozem medium-thick medium-humus heavy loamy soil; solonetz meadow chernozemic deep low humus clay soil. The largest area on the last round of agrochemical survey of 1194.3 thousand ha (58.9%) has an average humus content (4.1-6.0%), it increased significantly from 784.5 thousand ha (38.7%). The increased and high (> 6%) humus content significantly decreased over the study period by 416.5 thousand ha from 1118.5 (55.1%) to 702.0 thousand ha (34.6% of the surveyed area). The weighted average humus content over 28 years has changed: from 6.2 to 6.0% in the northern forest-steppe, from 6.0 to 5.3% in the southern forest-steppe, on average it is by 0.5%. A tendency toward a decrease in the humus content of soils remains in the soils of the Omsk Priirtyshye region. The main reason for this is both the ongoing water and wind erosion of soils, and the very low level of organic fertilizers use. The authors revealed the gradual decrease in the content of humus in ordinary chernozems and meadow chernozem soils. There was a stable humus content in the arable horizon of the solonetzes of deep meadow-chernozem soils.

The studies developed agrochemical regulatory parameters for the use of organic fertilizer based on litterless chicken manure for managing potato nutrition on meadow-chernozem soil in the forest-steppe of Western Siberia. The place of research was the experimental field and the department of agrochemistry and soil science of the FSBEI HE Omsk State Agrarian University in 2012-2014. The studied objects included potato plants of the Alaya Zarya variety and meadow-chernozem medium-thick medium-humus medium-loamy soil. Potatoes formed a yield of 22.9 t / ha without fertilizers and 26.0-33.2 t / ha with fertilizers. The use of 12 t / ha was the most effective because the yield increases in 10.3 tons or 45.0%, the payback of 1 ton of manurewas0.86 tons of tubers. 1 ton of litterless manure increases the concentration of N-NO3 by 2.06 mg/kg, P2O5 - 2.73 and K2O - 1.28. The authors established quantitative characteristics of the action intensity of 1 ton of manure on potato yields (1.14 t/ha) and proposed a formula of calculating doses for a planned increase in yield based on this study. They identified a normative indicator (coefficient b2) of the action intensity of 1 t/ha of manure on the nitrate-nitrogen content, mobile phosphorus and potassium. It allows to predict their accumulation in the soil and to determine the dose of fertilizers considering the optimal and actual content of the nutrient element in the soil.

This research is based on local monitoring in 1994-2018 on reference plots of agricultural lands and materials of a large-scale agrochemical survey. The research examined the soils of the forest-steppe zone of the Omsk Region: ordinary chernozem low-power low-humus heavy loamy soil; meadow-chernozem medium-thick medium-humus heavy loamy soil; and solonetz meadow chernozemic deep low humus clay soil. It was found that almost the entire surveyed area of arable land in the forest-steppe zone of the Omsk Irtysh Land (98.1 %) had low mobile zinc availability with an average level of 0.85 mg/kg. 41.1% of arable land had low mobile manganese availability, 41.3% had medium and 17.6% had high availability; the weighted average was 13.0 mg/kg. Most of the arable land was characterized by a low degree of mobile copper content security (81.2%), while 18.3% of the land had soil with an average content, and only 0.5% of the land had high mobile copper content. The average concentration was 20.0 mg/kg. The soil levels of mobile molybdenum availability wereas follows: 71.6% of land had medium availability, 26.5% had high, and only 1.9% had low; the weighted average concentration was 0.20 mg/kg. All soils had a high degree of mobile forms of boron, while the weighted average was 2.69 mg/kg of soil. 67.8% of the area had low mobile cobalt availability, 31.6% had average availability, and 0.5 % had high availability, with an average concentration of 0.16 mg/kg in the zone. The reference plots did not differ in terms of their content of mobile zinc, copper, and cobalt, ordinary chernozems, meadow chernozem soils, and deep solonetz. Movable connections of molybdenum, manganese, and boron in ordinary chernozem were lower than in meadow chernozem soil, and the maximum ones were observed in solonetz meadow chernozemic deep. Keywords: trace elements, content, soil, survey, dynamics, Omsk region

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