Suitable Sources of Nitrogen and Potassium Fertilizer for Fertigation of Northern Highbush Blueberry

Many blueberry growers are switching from broadcasting granular fertilizers to using fertigation through a drip irrigation system. Fertigation increases growth and production without increasing the need for more fertilizer. The objective of the present study was to evaluate different liquid sources of N and K fertilizers for fertigation in northern highbush blueberry (Vaccinium corymbosym L.). The study was conducted in a greenhouse using potted plants of ‘Duke’ blueberry. Treatments included a combination of the two soil types [optimum (4.9) and high pH (6.2)], two liquid K sources [(potassium sulfate and potassium thiosulfate (KTS)], five liquid N sources [urea, ammonium sulfate, ammonium thiosulfate (ATS), urea ammonium nitrate (UAN), and urea-triazone (slow-release N); 0.10 g·L^-1 N each), and five K rates (0, 0.05, 0.10, 0.15, and 0.20 g·L^-1). The plants were fertigated three times per week with each combination of K and N fertilizer, plus a modified Johnson’s solution to avoid limitations of other nutrients. Fertigation with ATS and/or KTS reduced soil pH by at least a unit within 1–3 weeks in both of the soils. On average, the concentration of K in the soil solution increased by 25% with potassium sulfate and by 39% with KTS, and was highest when KTS was applied with urea or ammonium sulfate. The concentration of Ca and Mg also increased with the K fertilizers and was greater with KTS. Overall, KTS appears to be a good source of K for fertigation in blueberry and is recommended for use with urea on soils with optimum pH (4.5–5.5) and with ammonium sulfate on soils with high pH.