The changes in agroecological soil parameters were investigated: humus content, alkaline hydrolyzed nitrogen, mobile phosphorus, exchangeable potassium, soil solution pH reaction, hydrolytic acidity, soil content of mobile forms of heavy metals: lead, cadmium, copper and zinc; soil erosion resistance parameters: proportion of agronomically valuable and water-resistant aggregates, structural coefficient and bulk density of gray podzolized soil depending on the duration of cultivation of alfalfa (Medicago sativa L.). The soil of the experimental plot is gray podzolized medium loam. Alfalfa (Medicago sativa L.) was grown for four years with soil samples taken for laboratory analysis at the end of the second and fourth years of vegetation. Alfalfa (Medicago sativa L.), as a legume perennial grass, when grown for four years, exhibits powerful phyto-ameliorative properties: it increases the humus content in gray podzolized medium loam soil by 0.1%, alkaline hydrolyzed nitrogen by 2.9%, mobile phosphorus by 8.0%, exchangeable potassium by 25.6%. It optimizes the pH reaction of the soil solution, increasing it from 0.1 to 0.3 pH, achieving a neutral reaction in the range of 7.1-7.3 pH and reduces hydrolytic acidity by 24.5-28.3%. It reduces the mobility of heavy metals in the soil, which reduces their concentrations by 39.0% – lead, by 96.7% – cadmium, by 98.5% – copper and by 87.9% – zinc. The positive role of alfalfa (Medicago sativa L.) in increasing soil erosion resistance. It is manifested in an increase in the share of agronomically valuable soil aggregates by 4.9-6.7%, water-resistant aggregates by 32.2%, and the soil structural coefficient by 1.1-1.6. An additional positive factor in growing alfalfa is soil loosening, which is manifested in a decrease in soil bulk density by 5.0-33.3% to a value of 1.14 g/cm3.