Elena Vyacheslavovna Leonicheva

The purpose of the research was to study interannual and seasonal dynamics of mobile potassium compounds in orchard soil and potassium status of apple trees affected by foliar and ground fertilization with potassium and nitrogen. The investigation was carried out in 2016-2020 growing seasons in soil-climatic conditions of forest-steppe zone of the Central Russian Upland (Orel region). The experiment studying mineral fertilizers’ efficiency has been running since 2015 in the apple orchard with cv.’Ven’yaminovskoe’. The 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. The 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. The level of mobile potassium in root zone of unfertilized plots was relatively constant during five years. At the same time the regular ground fertilization led to gradual accumulation of potassium in the topsoil. The accumulation rate depended on the doses of fertilizers. When the soil potassium content reached a range 150 mgkg-1 the seasonal fluctuations of index have intensified and vertical migration of potassium occurred. The main factors affecting potassium regime of apple trees were: weather conditions, yield and fertilization rates. Conjugate soil and plant diagnostics showed that the negative effect 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. The highest yield of apple trees in first four years of fruiting observed with soil fertilization by N60K80 in combination with foliar sprays.