Limitations of CaCl₂ salinity to shoot and root growth and nutrient uptake in ‘Honeoye’ strawberry (Fragaria × ananassa Duch.)

Salinity thresholds are required to develop better water and nutrient management practices for the production of saltsensitive crops such as strawberry (Fragaria × ananassa Duch.). To determine these thresholds, ‘Honeoye’ strawberry plants were grown in soilless media, fertigated daily with five concentrations of CaCl₂ [0 (control), 5, 10, 15, and 20 mM] plus a complete nutrient solution with each, and harvested for growth and nutrient analysis after 31, 58, 87, and 114 d of treatment. To adjust for plant growth, CaCl₂ concentrations were doubled in each treatment after 90 d. The electrical conductivities (ECs) of the solutions increased by approx. 0.2 dS m–¹ for each 1.0 mM CaCl₂ added. Salinity had no effect, relative to the 0 mM CaCl₂ control, on the dry weights (DWs) of leaves, crowns, or mature primary roots, but CaCl₂ concentrations ≥ 10 mM or ≥ 15 mM reduced the DWs of stolons by 15 – 32% and of new daughter plants by 5 – 22%, respectively, at 87 d. Salinity also reduced the DWs of new primary roots by 40 – 48% and feeder roots by 19% at 114 d at ≥ 30 mM or 40 mM CaCl₂, respectively; whereas 10 mM CaCl₂ increased the DWs of feeder roots by 33%. Marginal leaf necrosis was evident in each treatment and, by 113 d, occurred on 14% of leaves treated with 0 mM CaCl₂, on 51 – 79% of leaves treated with 10 – 20 mM CaCl₂, and on 93 – 98% of leaves treated with 30 – 40 mM CaCl₂. Treating with CaCl₂ not only increased the Ca in each plant organ, but also increased the concentrations of other nutrients, although not always at the highest CaCl₂ concentration. This included Fe in leaves, stolons, and daughter plants, B in daughter plants, and Zn in crowns, daughter plants, and feeder roots. Most of the other nutrients measured were reduced by CaCl₂ salinity, including N in stolons, daughter plants, new primary roots, and feeder roots, P and Mn in all tissues/organs but feeder roots, K in all tissues/organs but leaves, Mg in all tissues/organs but crowns, S in daughter plants and each root part, and B and Zn in new primary roots. These results indicate that to achieve optimum growth and runner production in strawberry, irrigation and fertiliser levels should be managed to maintain the EC of the soil (or the nutrient solution) at ≤ 1.3 dS m–¹ during the first 3 months after planting, and at ≤ 3.4 dS m–¹ once the plants have matured.