The 2011 ASHS Annual Conference

Rhizosphere environment is critical in the production of healthy and vigorous plants. Blueberry (Vaccinium  corymbosum)  is known to thrive in low pH environments. Nitrogen forms {nitrate (NO₃) and ammonium (NH₄)} and ratios (NH₄^:NO₃) affect rhizosphere pH, which ultimately dictate the bio-availability of macro and micronutrients. Two experiments were conducted to investigate the range of nutrient solution pH, and nitrogen (N) forms and ratios on the root and shoot performance in blueberry. One year old seedlings were grown at six pH levels (4.5, 5.0, 5.5, 6.0, 6.5, and 6.8) in calcined clay and wood charcoal soilless substrates, and fertigated with 3.57 mM concentration of (NH₄^:NO₃)-N at two and one hour intervals in the morning and afternoon, respectively.  Nutrient solution at pH 6.0 and below produced higher shoot and root fresh and dry mass. In the second experiment, the plants were supplied with 5.0 mM concentration of five different ratios of NH₄^:NO₃-Nitrogen nutrient solution: a) 100:0, b) 50:50, c) 25:75 and d) 0:100 at pH of 5.5 and 6.0. Plants fed with mixed NH₄ and NO₃ – N at pH of 5.5 produced higher shoot and root fresh and dry mass. Nutrient solution supplied at pH of 6.0 consistently produced lower shoot plant biomass irrespective of NH₄:NO₃-N forms and ratios.  The NH₄:NO₃ (75:25) - N form nutrient solution supplied at pH of 5.5 treatment produced the highest fresh and dry mass. The 100% NO₃-N nutrient solution treatment supplied at pH of 5.5 and 6.0 produced the lowest shoot and root mass, and the foliage of these plants appeared reddish.