The Effect of Soil Nutrition and Foliar Fertilizers on the Soil Potassium Regime and Potassium Status of Apple Trees in a Rainfed Orchard

Abstract

The purpose of this research was to study the interannual and seasonal dynamics of mobile potassium compounds in orchard soil and assess the potassium status of apple trees influenced by foliar and ground fertilization with potassium and nitrogen. The research was carried out in 2016–2020 growing seasons under soil-climate conditions of the forest-steppe zone of the Central Russian Upland (Orel region). The field experiment studying the efficiency of nitrogen and potassium fertilizers has been running in the apple orchard with apples of cv. “Venyaminovskoe” since 2015. The soil of the experimental orchard is loamy Haplic Luvisol. Ammonium nitrate and potassium chloride were used as soil fertilizers at doses of 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 that were monthly taken from a depth of 0–20, 20–40, and 40–60 cm from May to September. The level of mobile potassium in the root zone of unfertilized plots was relatively constant during the five years. At the same time, the regular ground fertilization led to a gradual accumulation of potassium in the topsoil. Its accumulation rate depended on fertilizer doses. When the soil potassium content reached 150 mg/kg, the seasonal fluctuations of the index increased and vertical migration of potassium began to be observed in the soil profile. The main factors influencing the potassium regime of apple trees were weather conditions, yield, and fertilization rates. A correlated soil and plant diagnosis has shown that the negative effect of the decrease in the availability of soil potassium also persists in the subsequent growing season; however, it can be weakened using soil and foliar fertilizers. The highest yield of apple trees in the first four years of fruiting was observed when the soil was fertilized with N60K80 in combination with foliar sprays.