Effects of Method and Level of Nitrogen Fertilizer Application on Soil pH, Electrical Conductivity, and Availability of Ammonium and Nitrate in Blueberry

Blueberries (Vaccinium spp.) require low soil pH and prefer N primarily as ammonium for optimum production. Nitrogen fertilizer methods and rates were evaluated in a new field of `Bluecrop" blueberry (Vaccinium corymbosum L.) to determine their effects on soil pH and availability of ammonium and nitrate in soil solution. Treatments included four application methods (split fertigation, continuous fertigation, and two non-fertigated controls) and four rates of N application (0, 50, 100, and 150 kg/ha N). Fertigation treatments were irrigated by drip and injected with liquid urea fertilizer; split fertigation was applied as a triple-split from April to June while continuous fertigation was applied weekly from leaf emergence to approximately 2 months prior to the end of the growing season. Non-fertigated controls were fertilized with a triple-split of granular ammonium sulfate and irrigated by drip or microsprays. Soil pH was usually lower with microsprays than with drip, even when no N fertilizer was applied; however, soil pH was also reduced with higher N applications and, in fact, was similar between continuous fertigation and granular fertilizer (microspray) treatments when 150 kg/ha N was added. Nitrogen application with granular fertilizer, whether irrigated by microspray or drip, maintained much higher ammonium concentrations than continuous or split fertigation but often increased electrical conductivity (salinity) of the soil solution (ECw) to >2 dS/m. By comparison, ECw was always <1.5 dS/m with either fertigation method. Granular N application coupled with microsprays also resulted in higher nitrate concentrations than any other treatment, which may lead to more N leaching since the ability of blueberry to acquire nitrate-N is limited