The paper highlights the results of many-year (1982-1992, 2011-2014 гг.) research on the concentration of mineral nitrogen in the arable medium peat soil layer of the forest-steppe of Trans Urals zone. The research was carried out on the experimental-reclamation system Reshetnikovo located in the central part of the Tarman bog on the second lacustrine-alluvial basin of the Tura River in Tyumen region. The soils on the experimental plot have a slightly acidic reaction (5.2 - 5.9), relatively low

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... hydrolytic acidity (28.1 - 40.8 mg-eqv/100 g of soil), relatively low degree of base saturation (61.7 - 75.5%), high gross nitrogen concentration (3.1 - 3.9%), low concentration of phosphorus (0.09 - 0.14%) and potassium (0.02 - 0.05%). The researchers found out that mineralization of peat is slow and almost always fails to provide sufficient and continuous supply of nitrogen, despite its large gross reserves. Due to insufficient number of mobile nitrogen compounds from peat organic matter during the growing season it is necessary to apply nitrogen fertilizers. When peat soils contain low concentrations of phosphorus (0.7 - 3.7 mg/100 g of soil), the highest number of nitrate nitrogen is accumulated in the arable layer under perennial grasses due to its low consumption for the yield. Re-reclaimed peat soil is characterized by negative nitrogen concentration. As perennial grasses require nitrogen, it is fulfilled by means of fertilizers on 41.4 - 72%. The authors observed a tendency of reducing nitrate reserves under perennial grasses even if nitrogen fertilizers are applied. This indicates a decrease in the mineralization rate of peat organic matter. The ammonium nitrogen concentration increases. Discontinuance of nitrogen fertilizers use reduces the nitrate nitrogen concentration on 30-49% in the first year and on 46.7-59.1% by the end of the fourth year of after-effect. The amount of ammonium nitrogen increases in 1.6-3.7 times in 4 years.