THE EFFECT OF MAGNESIUM SULFATE ON THE YIELD OF "СOLKHIDA" TEA CULTIVARS ON THE BLACK SEA COAST OF RUSSIA

Growing tea in the humid subtropics of Russia with prolonged use of macro fertilizers in high doses significantly impoverishes the tea-suitable soils in the region (brown soils) with exchangeable magnesium, which is the result of its increased mobility against the background of high soil acidity. At the same time, the need for Md in tea plants is sufficiently high, and magnesium fertilizers in the system of mineral nutrition for the crop are insufficiently studied. In the field experiment, the effect of root application of magnesium sulfate (based on Mg60) with macro fertilizers in optimal doses (N240P70K90 – control) on the yield of the intensive ‘Colkhida’ tea cultivar was studied. It was found that against the background of magnesium deficiency in the soil (0.4–0.6 mg-eq/100 g), the annual introduction of MgSO4 during the first 9 years (2003–2011) had a positive effect. The yield of tea leaves was on average 25 % higher than the control (6.2 and 4.9 t/ha, respectively). In subsequent years, against the background of an increased availability of magnesium in the soil (up to 2.5–3.0 mg-eq/100 g), the positive effect of the application ceased to manifest itself. In the period 2012–2015, the average yield with the introduction of magnesium (5.0 t/ha) was even slightly lower than the control (5.3 t/ha). The use of magnesium sulfate was discontinued. With its aftereffect, over the next 5 years (2016–2021), the yield remained at a level close to the control (3.7 and 3.9 t/ha, respectively). In general, for the period 2012–2021, tea yield on the studied variant varied significantly (2.1–8.6 t/ha) depending on meteorological conditions. In favorable years, it reached on average 6.2 t/ha and did not differ from the control. In more difficult meteorological conditions (spring frosts and summer drought), the yield averaged 2.8 t/ha, which was 12.5 % lower than the control. The decrease in yield is associated with deterioration in the overall functional state of plants, including a more significant violation of the water regime for plants on the variant with MgSO4 in the summer period. With water deficiency and soil drought, the concentration of cell juice in flushes increased here to 9.4–15.0 % (in some years up to 20 %), which was on average 1.3 times higher than the control indicators.