|MACHADO, RUI - UNIVERSITY OF EVORA|
|VARGAS, OSCAR - OREGON STATE UNIVERSITY|
Submitted to: Acta Horticulturae
Publication Type: Proceedings
Publication Acceptance Date: 11/8/2012
Publication Date: 1/10/2014
Citation: Machado, R., Bryla, D.R., Vargas, O. 2014. Effects of salinity induced by ammonium sulfate fertilizer on root and shoot growth of highbush blueberry. Acta Horticulturae. 1017:407-414.
Technical Abstract: Ammonium sulfate fertilizer is commonly used in highbush blueberry, but due to a high relative salinity, it often causes salt damage, particularly in young plants, when too much of the fertilizer is applied. Three experiments were done to determine the sensitivity of ‘Bluecrop’ blueberry to ammonium sulfate and identify the salinity threshold in which plant growth was affected by the fertilizer. In the first experiment, plants were grown in pots and fertilized two to three times per week with four rates of 0, 0.25, 0.75, and 1.5 g/L ammonium sulfate solution. Electrical conductivity (EC) of the solutions increased linearly with fertilizer rate and averaged 0.1, 0.5, 1.5, and 3.0 dS/m, respectively. Plants fertilized with 1.5 g/L ammonium sulfate produced less leaves and roots and had a lower leaf to stem dry weight ratio than those fertilized with 0 or 0.25 g/L, which indicates that root and leaf growth in blueberry was sensitive to EC > 1.5 dS/m. In the second experiment, plants in pots were fertilized with ammonium sulfate or urea at a frequency of 3 days per week, weekly, or every 28 days, using the same total amount of nitrogen (N) in each treatment over a 4-week period. In this case, plant growth was higher with ammonium sulfate than with urea but also higher, regardless of fertilizer source, when plants were fertilized more frequently. In the third experiment, plants were grown in the field with no N fertilizer or with ammonium sulfate or urea applied either by fertigation weekly or by a triple-split application of granular fertilizer at a total rate during the third year after planting of 133 kg/ha N. Yield in the young plants was greater with fertigation or with granular urea than with the granular ammonium sulfate, the latter of which resulted in EC levels in soil solution as high as 13 dS/m. In the field, fertilizer programs and practices such as fertigation that maintain EC < 2 dS/m are recommended for highbush blueberry.