Effects of Salinity Induced by Ammonium Sulfate Fertilizer on Root and Shoot Growth of Highbush Blueberry

Abstract

Abstract Ammonium sulfate fertilizer is commonly used in highbush blueberry (Vaccinium corymbosum L.) but often causes salt damage, particularly in young plants, when high rates are applied. Three experiments were done to determine the sensitivity of ‘Bluecrop’ blueberry to ammonium sulfate and identify the salinity threshold at which plant growth was affected. In the first experiment, plants were grown in pots and fertigated two to three times per week with 0, 0.25, 0.75, and 1.5 g·L-1 ammonium sulfate solution. Electrical conductivity of the solutions (ECw) increased linearly with fertilizer rate and averaged 0.1, 0.5, 1.5, and 3.0 dS·m-1, respectively. Plants fertigated with 1.5 g·L-1 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-1, which indicates that root and leaf growth in blueberry was sensitive to ECw > 1.5 dS·m-1. In the second experiment, plants in pots were fertilized with ammonium sulfate or urea at a frequency of three times 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 by weekly fertigations or by a triple-split application of granular fertilizer at a total rate of 133 kg·ha-1 N during the third year after planting. Yield in the plants was greater with fertigation or with granular urea than with granular ammonium sulfate, the latter of which resulted in ECw levels in the soil solution as high as 13 dS·m-1. In the field, fertilizer programs and practices such as fertigation that maintain ECw < 2 dS·m-1 are recommended for highbush blueberry.