Site description and experimental design
The experiment was conducted using ‘Honeycrisp‘ grafted onto 9 different rootstocks at Washington State University (WSU) Sunrise Research Orchard in Rock Island, WA (47°18’35.6”N 120°03’59.5”W). The soil is a shallow sandy loam soil with good drainage. The rootstocks in this experiment were: Budagovsky- 9 (B.9), CG.4292, CG.5257, M.9-T337, Geneva 210 (G.210), Geneva 814 (G.814), Geneva 87 (G.87), Geneva 890 (G.890), and Geneva 969 (G.969). The dwarfing capacity of these rootstocks ranged from dwarfing (B.9) to semi-vigorous (G.890). The experiment was planted in 2017 and arranged in a completely randomized design (N = 3) with three to eight trees per replication. The orchard was oriented north to south and rows were spaced 3.6 m apart and 0.9 m between trees which were trained to a spindle system and irrigated using at approximately 110% replacement of estimated evapotranspiration during the growing season using a combination of drip and micro-sprinklers. Trees were managed and pruned according to commercial tree fruit management practices. In 2018 and 2019, flowers were completely removed from the trees to eliminate any cropping during early growth. Soil volumetric water content and soil temperature were measured using an ECH2O 5TM soil moisture and temperature probe (Meter Group, Pullman, WA, USA) (Table 1). Three soil moisture sensors were placed in different locations in the herbicide strip equidistant between two trees at 20 cm depth. Relative humidity and air temperature were measured with a VP-3 sensor placed in the middle row 1.8 m above ground. Each soil probe, air temperature, and relative humidity sensors were interfaced with an EM50G data logger (Decagon Devices, Pullman, WA, USA) and data were logged every 15 minutes from April to September. Solar radiation and wind speed were obtained through the AgWeatherNet weather stations located immediately adjacent to the WSU-Sunrise Orchard (https://weather.wsu.edu/).