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 due to a high salt index, it often causes salt damage, particularly in young plants, when too much of the fertilizer is applied. A study was done to determine the sensitivity of blueberry to ammonium sulfate and identify the salinity threshold in which plant growth is affected by the fertilizer. One-year-old ‘Bluecrop’ blueberry plants were transplanted from 0.5-L pots to 8-L pots filled with a 1:1 (v/v) mixture of peat and pine bark and fertilized with four rates of 0, 0.25, 0.75, and 1.5 g•L-1 ammonium sulfate solution. Each solution was applied 2-3 times per week as needed for a total of 8 weeks. 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. Fertilizer rate had no effect on total shoot dry weight but significantly affected new root dry weight and partitioning of shoot biomass. Plants fertilized with 1.5 g•L-1 ammonium sulfate produced less 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 between 1.5 and 3.0 dS•m-1. In the field, fertilizer programs and practices (e.g., fertigation) that maintain ECw in soil solution < 1.5 dS•m-1 are recommended for rapid establishment of highbush blueberry.