NITROGEN RATE AND TIME OF SAMPLING EFFECTS ON SOIL TEST VALUES CF HIGHBUSH BLUEBERRIES GROWN ON A MINERAL SOIL

Abstract

Nitrogen rates (using urea) of 22, 67 and 135 kg/ha were applied to mature mulched and unmulched highbush blueberries over a 5 year period. Soil samples were taken each year at budbreak (prior to fertilization) and post-harvest at the suggested time of foliar sampling (approx. Aug.1) to determine N rate effects within and among years. Data analysis revealed that the most common soil test variables affected by N rate and date of sampling were pH, electrical conductivity (EC) and nitrate. For unmulched plants, a significant reduction in soil pH was found each year between budbreak and Aug. 1 for the 67 and 135 kg/ha rates, but not usually for the 22 kg/ha rate. For mulched plants, pH reduction within N rate among sample dates was usually not significant. Overall soil pH reduction was greatest for the 135 kg/ha rate over the 5 years, and the pH reduction for the 67 kg/ha rate was similar to the 135 kg/ha rate for the unmulched plants. For mulched plants, 22 and 67 kg/ha rates had a similar trend of only a slight pH reduction over the 5 years. EC and nitrate trends were very similar, with the highest levels of each on the unmulched plants.