OPTIMUM LEVELS OF EXCHANGEBLE MAGNESIUM IN THE PODZOLUVISOL LOAM SOIL AND EFFICIENTCY OF THE SULFER-CONTAINING FERTILISERS FOR CORN PRODUCTION
Field trials were conducted in 2010-2013 years on the Podzoluvisol light loam soils on four different levels of the exchangeable magnesium content (1 n. КСl) has been presented. The levels of exchangeable magnesium are: 74-77; 120-144; 181-195; 240-263 mg kg<sup>-1</sup> Mg. The equivalent cation ratios on presented levels has corresponding significances: Ca<sup>2+</sup>:Mg<sup>2+</sup>=10,7-13,2; 6,5; 3,9-4,0; 2,7-2,9 and К<sup>+</sup>:Mg<sup>2+</sup>=1,04-1,30; 0,55-0,64; 0,33-0,48; 0,21-0,36. It was determined accounting range of the optimum content of the exchangeable magnesium in soil (180-240 mg kg<sup>-1</sup> Mg) and equivalent cation ratios of the soil absorbing complex (Ca<sup>2+</sup>:Mg<sup>2+</sup>=3,5-4,0; К<sup>+</sup>:Mg<sup>2+</sup>=0,3-0,5) for receiving of the high productivity of green mass and grain corn. Essential gains of green mass corn yield - 5,0-2,6 t/ha and grain corn yield - 0,74-0,28 t/ha was obtained when a foliar spray of Mg fertilizer (1 kg/ha, 4% MgSO<sub>4</sub>·7H<sub>2</sub>O) was applied only on the low and medium contents of the exchangeable magnesium in the soil. Application of the 60 kg/ha sulfur fertilizers allowed to obtain gains of green mass corn are 2,0-7,7 t/ha at the magnesium content in the soil not higher than 181 mg/kg. Phospogypsum in contrast with the ammonium sulfate fertilizer was more efficiency.