Changes in the content of mobile potassium in the soils of the forest-steppe of Western Siberia

The research is based on the results of local monitoring in 1994-2018 on reference plots laid on agricultural lands and on the archival materials of a large-scale agrochemical survey carried out in 1965-2018. The objects of research were the soils of the forest-steppe zone of the Omsk Region: ordinary chernozem with low fertility, low humus and high loamy content; meadow-chernozem with average fertility, average humus and high loam content; deep meadow-chernozem solonetz with low humus and low clay content. Almost all arable soils of the southern forest-steppe (98.5%) have high and very high potassium content (> 120 mg/kg of soil). In the northern forest-steppe, such soils account for only 44.8%. In general, the arable soils of the forest-steppe zone of the Omsk Irtysh Region have a high and very high content of mobile potassium on an area of 1.495.6 thousand ha (73.8%), but their share is gradually decreasing by an average of 0.01% per year. Over the 25-year monitoring period, the weighted average content of mobile potassium in the arable layer of ordinary chernozem reference plots decreased from 191.2 to 186.0 mg/kg of soil, on meadow-chernozem soils from 187.2 mg/kg to 179.4 mg/kg of soil. Its content in solonetzes of deep meadow-chernozem soils remained at the same level (174.0-175.4 mg/kg of soil).