Differential Susceptibility of Strawberry to Salts.

Strawberry is a primary crop in coastal California, with annual value of $ 1.4 billion.  Bare-root strawberry transplants are very sensitive to salts during the first 3-5 weeks after planting when the new root systems begin to develop.  Even though current EC (Electrical Conductivity, a measure of salinity) threshold for yield reduction is 1 dS/m, several strawberry fields have excellent production in soils with EC 4-6 dS/m. Thus, we investigated effects of the specific salts on strawberry in summer and fall-planted strawberry in typical 1.2 m-wide raised beds covered with plastic mulch in clay loam soil near Santa Paula, CA.

In two replicated RCBD experiments initiated in June (proprietary variety) and October (Benicia) transplants were irrigated nine times during establishment period with 250 ml/plant of either distilled water or one of four salt solutions of potassium sulfate, sodium sulfate, calcium chloride or sodium chloride diluted to achieve at EC 5, 10, 15 or 20 dS/m).  Standard grower production practices were followed during the remainder of the season.

Sulfate concentrations at EC 5 dS/m did not affect fruit production in summer or fall strawberry, while plants irrigated with sodium or calcium chlorides were 65% or 85% smaller than distilled water irrigated plants and failed to produce fruit.  At greater EC values, fruit production declined 30-80% for the sulfates and was near zero for chlorides at EC >5dS/m. The negative effects of all salts were more pronounced in summer, likely due to higher evapotranspiration rates and lack of rain. Linear relationships between concentrations of each of the salts and strawberry fruit yields were developed and did fit the data well. The study emphasized the need for testing for specific ions in irrigation water instead of relying solely on EC measurements for management decisions.