Interaction of drought stress and potassium deficiency on soybean vigor and leaf temperature

Potassium (K) nutrition and drought stress affect soybean (Glycine max (L.) Merr.) vigor and productivity through the combined impacts on water regulation. A study was conducted with soybean grown in 18.9-L buckets under a rain out shelter to determine how the interaction between these crop stresses at various growth stages influences the crop leaf K concentration, biomass production, total K uptake (TKU), grain yield, and temperature of the uppermost fully expanded trifoliate. Treatments included soybean grown with and without preplant fertilizer K, soil moisture at 50% (drought) or 80% (well-watered) field capacity, imposed drought during vegetative growth (V3–V7), flowering (R1–R3), pod development (R4–early R6), and seed development (R5–mid-R6) on two different silt loam soils. Widespread K deficiencies were observed during the study across all treatments. Drought stress significantly (p < 0.05) reduced the TKU, aboveground biomass production, and grain yield. The crop growth stage when drought stress was imposed was a significant factor, with greater reductions in plant response parameters when stress was imposed during reproductive growth. Preplant fertilizer K increased trifoliolate K concentrations and TKU in drought conditions, but did not increase the grain yield of well-watered soybean. Leaf temperature increased when under drought stress compared to well-watered soybean (p < 0.0001) but the impact of crop K nutrition status on leaf temperature was inconclusive because of widespread K deficiencies. Results emphasize the complexity of the interactions between K nutrition and drought stress in soybean, as drought stress impeded K uptake, exacerbated K deficiencies, and limited yield.