The paper presents the results of long-term observations of the agricultural land transformation into natural phytocenoses. The comparative analysis of sustainability and biodiversity of two closely located Plots No. 1 and No. 2 showed that the initial state of the land mainly determines these indicators. The transformation of well-cultivated fallows of Plot No. 1 was with a sufficiently high rate of succession. It led to the disturbance of the ecosystem, the degradation of the phytocenosis and a low level of biodiversity and productivity. A decrease in the number of almost all entomophilous plants, including Fabaceae, Asteraceae, from 25.6% to 3.4% was on the plot in the period from the 6th year. Moreover, there were shrubs of the test plot with birch the appearance of dominant species, by nettle and willow-herb. The transformation of seeded herbage with a Legume component of Plot No. 2 by the year 8 led to the displacement of sown grasses, the emergence of synusia with a high density and biomass of plants based on hybrid clover and Poaceae. They occupied a large area of Plot No. 2 and determined a steady state of the biocenosis with high biodiversity and productivity, with the retention of a high number of Fabaceae in the herbage from 9 to 16% for a long time. The paper indicates that the management by the initial state of phytocenoses, in particular, haymaking and a clover-cereal mixture sowing, makes it possible to change the direction of transformation of biocenoses and carry out long-term planning and restoration of their stability and biodiversity.