THE EFFECT OF SOIL NUTRITION AND FOLIAR FERTILIZERS ON SOIL POTASSIUM REGIME AND POTASSIUM STATUS OF APPLE TREES IN RAINFED ORCHARD

Abstract

Th e purpose of the research was to study interannual and seasonal dynamics of mobile potassium compounds in or-chard soil and potassium status of apple trees aff ected by foliar and ground fertilization with potassium and nitrogen. Th e investigation was carried out in 2016–2020 growing seasons in soil-climatic conditions of forest-steppe zone of the Central Russian Upland (Orel region). Th e experiment studying mineral fertilizers’ effi ciency has been running since 2015 in the apple orchard with cv.’Ven’yaminovskoe’. Th e soil of the experimental orchard is loamy Haplic Luvisol. Ammonium nitrate and potassium chloride were used as soil fertilizers with doses N30K40, N60K80 and N90K120. Urea (1%) and potassium sulfate (0,3%) solutions were used for foliar fertilizing. Th e content of mobile potassium compounds was determined in soil samples taken from a depth of 0–20, 20–40 and 40–60 cm monthly from May to September. Th e level of mobile potassium in root zone of unfertilized plots was relatively constant during fi ve years. At the same time the regular ground fertilization led to gradual accumulation of potassium in the topsoil. Th e accumulation rate depended on the doses of fertilizers. When the soil potassium content reached a range 150 mg∙kg-1 the seasonal fl uctuations of index have intensifi ed and vertical migration of potassium occurred. Th e main factors aff ecting potassium regime of apple trees were: weather conditions, yield and fertilization rates. Conju-gate soil and plant diagnostics showed that the negative eff ect of a decrease in the availability of soil potassium persists in the subsequent growing season, while can be weakened by applying soil and foliar fertilizers. Th e highest yield of apple trees in fi rst four years of fruiting observed with soil fertilization by N60K80 in combination with foliar sprays.