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Based on the economic reasons, the agrarians refused to apply organic fertilizers on arable land. Nowadays, to obtain high yields of agricultural crops, agrochemicals have been actively used, which led to organic matter shortage entering the soil. Straw, as a by-product, is usually removed from fields, which aggravates the situation on arable land. Moreover, this leads to deterioration of the humus state and nutrient regime of arable soil. The research objective was as follows: to study the dynamics of nutrient release from the plowed straw. The studies were carried out on the basis of Northern Trans-Ural State Agricultural University, located in the forest-steppe zone of the eastern margin of the Trans-Ural Plateau. The soil is leached chernozem, thin, formed on covering silt. The straw was collected from each area where mineral fertilizers were applied for the planned yield from 3.0 to 6.0 t/ha of grain. The straw was buried at various depths (10, 20, and 30 cm). It was established that immediately after the plowing up of plant residues in the autumn period, the nitrogen leaching was observed from the straw in the areas where fertilizer at various rates were introduced for the planned grain yield. In May, its concentration in the plowed up plant residues reaches 0.56-0.80% by weight. In June, the nitrogen concentration in the straw increases after the microflora growth on the surface of the plant residues. Different levels of mineral nutrition do not affect the release of phosphorus and potassium from the plowed up plant residues. The main amount of phosphorus and potassium from the plowed up straw is released in the period from October to June, reaching 0.11 and 0.10%, respectively.

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The paper contains an analysis of fertility changes in dark gray forest soils under man-made forests of Pinus sylvestris (L.) with the age of 15; 30; 45 and 60 years. The studies were performed in the territory of a forest enterprise located in Abatsky district of Tyumen oblast, in the northern forest-steppe of Western Siberia. Dark gray forest soil under a birch forest was used as a control. It has been established, that change in type of forest cover leads to changes in the species composition of the grass and shrub stratum. Humus state of the dark gray forest soils under man-made pine forests gradually deteriorates. Humus content reduces to 5.4% in the case where pines reach 60 years of age, while in the control plot under natural vegetation it amounts to 7.4% of soil mass. Qualitative composition of humus also gradually deteriorates: A fulvate-humate type is substituted with a humate-fulvate one, with low nitrogen enrichment. It has been established, that leaching is amplified under man-made pine forests with the age of under 45 years. Subsequently (60 years), podzolization starts in the dark gray forest soil, manifesting as destruction of soil adsorbing complex and increased acidity of the humus layer. In 45 years, base saturation decreased from 77% to 71% of the cation exchange capacity. Change in the humus state and chemical properties had a negative impact onto agrophysical properties of the dark gray forest soil. Water stability of structural aggregates gradually reduces from 65 to 42% with increased age of pine, while bulk density increases to 1.27 g/cm3. To prevent loss of fertility soils in Northern Trans-Ural, it is recommended to thoroughly analyze the plots planned under coniferous trees, to avoid their planting onto dark gray forest soils or soils similar in fertility. When moving such soils into arable lands, special measures are required for radical improvement in fertility (application of fertilizers, chalking) with subsequent sowing of perennial herbs.