ROTATION OF MAIN NUTRIENTS IN AGRICULTURE IN BELGOROD REGION
Agrochemical investigations from the first to the eighth five-year cycles were carried out in areas 15 585, 15 963, 15 589, 15 002, 14 629, 14 173, 13 736, and 13 107 sq km, correspondingly. Deficient nitrogen balance in soils of the region developed in 1964-1970 and 2000-2009, but its intensity in those years was quite admissible - 87.8...92.2 %. During 1976-1994 the intensity of nitrogen balance was 128.1...162.5 %. During 1984-2009 the weighted average content of easy hydrolysable forms of this element was 156...160 mg/kg and virtually did not change. In 1964-1994 phosphorus balance was positive, and in 1984-1989 its influx was 2.4 times higher its carry-over. In 2000-2009 the balance of this element became negative (intensity was 67.6...77.1 %), resulting in lower concentration of its mobile forms in soil by 15 mg/kg (11.5 %). Potassium balance in 1976-1983 was close to deficit-free one, and in 1984-1989 it was positive, but in other cycles of agrochemical inspection it was deficient. In 1990-2009 the weighted average content of mobile forms of this element was 126...128 mg/kg. In general, reducing of the fertilization use caused a significant deterioration of the main element balance of plant mineral nutrition in soils in Belgorod region. However, weighted average content of easy hydrolysable forms of nitrogen and mobile forms of potassium has not yet changed, and content of phosphorus mobile forms decreased by 11.5 %.