The objective of this study was to examine the effects of a spray application of magnesium chloride on pine seedlings. Magnesium chloride is used statewide in Colorado as a soil stabilizer on dirt roads and de-icing agent for roadways in winter. Magnesium chloride is replacing sodium chloride in these uses because of the reduced corrosive effects. However, little is known about the physiological effects of MgCl2 on roadside vegetation. With a controlled greenhouse experiment, we examined the effects of four concentrations of reagent-grade magnesium chloride (0 M, 0.74 M, 1.48 M, and 2.22 M) and one treatment of the commercially available magnesium chloride at the concentration applied to roads (3.15 M) on aboveground organs of one-year-old Pinus contorta seedlings. Chlorophyll content, shoot/needle dry weight biomass, and new needle growth at the apical shoots were measured over a 60-day period. Thirty days after the first spray application, necrotic needles were apparent on seedling exposed to the three highest concentrations of MgCl2, and lower chlorophyll contents were measured. Early results indicate that aerial drift of magnesium chloride on roadside vegetation can have an impact on pine health and vigor at the normal rates of commercial application and lower rates.

Key words: magnesium chloride, Pinus contorta, seedling growth