Impact of nitrogen forms and ratios, and substrate pH on blueberry (Vaccinium corymbosum) root and shoot development.

摘要

Rhizosphere environment is critical in the production of healthy and vigorous plants. Ericaceae species such as blueberry are able to grow in low pH environments. pH is a determining factor of substrate nutrient bio-availability. Nitrate and ammonium N-forms are contributing factors of rhizosphere pH. Two experiments were conducted with the objective to measure the effects of N-forms (NH4+ and NO3-), NH4:NO3 ratios and pH levels on root and shoot growth and development in blueberry grown in soilless substrate. To investigate the range of substrate pH on the root and shoot performance in blueberry, seedlings were grown at six pH treatments (4.5, 5.0, 5.5, 6.0, 6.5, and 6.8). 'Bluecrop and Legacy' blueberry ( Vaccinium corymbosum) seedlings were planted in soilless substrates: (1) calcined clay and (2) wood charcoal. Fertigated with a modified Hoagland nutrient solution with a 1:1 ratio of NH4:NO3- N at 3.57 mM N concentration. The second experiment was to investigate the effects of N-forms (NH4+ and NO3-), five NH4:NO3 ratios five ratios (100:0, 75:25, 50:50, 25:75, and 0:100), and pH of 5.5 and 6.0 on root and shoot growth and development in blueberry grown in soilless substrate.;The plant dry mass consistently peaked in the lower pH ranging from 4.5 - 5.5. Mild visual deficiencies symptoms of calcium appeared consistently higher in wood charcoal substrates grown at lower pH of treatments 4.5, 5.0 and 5.5. Plants grown in the nutrient solution pH 6.0 had higher growth than nutrient solution pH 6.5 and 6.8. Supplying nutrient solution containing 75:25% NH4:NO3-N form at a pH of 5.5 could be the desired N form and pH in creating the optimal rhizosphere for the normal growth of blueberry. Supplying NO3--N containing more than 25%, may affect blueberry growth significantly. In addition, if the nutrient solution pH were to be higher than 5.5 even at 75% NH4 +-N form, the plants initially appeared to grow poorly, but did seem to rebound at day 20.