Snowmelt erosion is one of the reasons for the decreasing soil fertility in the most valuable agricultural lands in the south of West Siberia. The aim of this study was to examine the influence of long term soil use and degree of soil erosion on the main fertility indicators of Greyzemic Phaeozem (30-year fallow, non-eroded, slightly eroded, moderately eroded and strongly eroded). Soils were analysed for organic carbon (SOC), pH w, cation-exchange capacity and total and available forms of nitrogen, phosphorus and potassium. Plants were analysed for sheaf and grain yield and NPK content of wheat. A decrease in the content of the total forms of carbon and nitrogen and an increase in the C/N ratio were observed with an increase in the degree of soil erosion. SOC losses in the ploughed layer of slightly, moderately and strongly eroded soils were 6.6, 13 and 27%, respectively, while the nitrogen losses were 5, 33, and 71%. The widest (37) C/N ratio was found in strongly eroded soil. The content of total phosphorus in the ploughed layer of slightly, moderately and strongly eroded soils decreased by 3.8, 23 and 15.4%, respectively, in comparison with non-eroded soil. Available forms of phosphorus and potassium increased with an increase in the degree of soil erosion, with the highest values found in moderately eroded soil. Exchangeable K/available K ratio, the overall mobility of potassium in the eroded soils also increased. The highest plant productivity was found on moderately eroded soil. A deterioration of the nitrogen regime led to a narrowing of the N/K ratio from 2.4 (grain) and 0.4 (straw) up to 1.9 (grain) and 0.3 (straw) for non-eroded and strongly eroded soils respectively. A critical decrease of soil fertility and plant productivity was found in strongly eroded soil.
