A Comparison of Ca and Mg Rates in Soilless Media for Optimum Vegetable Production Irrigated with Alkaline Water

Home gardeners residing in areas with alkaline city water sources do not have means of acidifying water for optimal vegetable production. A solution to achieving optimal yields with alkaline water is to use a specialized media; however, current media available does not meet these needs.  New media recipes with varied levels (0 to 8 lbs/yd³) and sources of Ca (dolomitic lime, gypsum) and Mg (dolomitic lime, magnesium sulfate) were tested using alkaline irrigation water on lettuce, cabbage, and cauliflower crops under high tunnel and on can yard sites.  Media treatments with the following fertilizer levels: 4lbs/yd³ gypsum and 4lbs/yd³ MgSO₄ (Ca/Mg); 4lbs/yd³ dolomitic lime (4L); 4lbs/yd³ dolomitic lime, 4lbs/yd³ gypsum, and 4lbs/yd³ MgSO₄ (4L+Ca/Mg); 8lbs/yd³ dolomitic lime (8L), outperformed a commercially available (IS) medium and the control (C) (no Ca or Mg fertilizer) medium in nearly all treatments with all crops.  All crops grown on the can yard and cabbage grown under the high tunnel had significantly greater yields when grown in medium 4L+Ca/Mg (80:20 bark:peat with 12 lbs/yd³ Osmocote^® Plus, 4 lbs/yd³ dolomitic lime, 4lbs/yd³ gypsum, and  4lbs/yd³ magnesium sulfate) compared to the IS and C media (p≤0.05).  Media treatment 4L (80:20 bark:peat with 12 lbs/yd³ Osmocote^® Plus and 4 lbs/yd³ dolomitic lime) produced significantly greater yields and plant growth of all tested crops on the can yard compared to the IS and C media (p≤0.05). Media longevity was tested by planting cucumber, tomato, and bell pepper into the same pots, at the same sites, during the spring with no additional pre-plant amendments added to the media.  All crops grown on the can yard, and cucumber and bell pepper grown under the high tunnel, had significantly greater yields grown in media 4L+Ca/Mg (80:20 bark:peat with 12 lbs/yd³ Osmocote^® Plus, 4 lbs/yd³ dolomitic lime, 4lbs/yd³ gypsum, and  4lbs/yd³ magnesium sulfate) or 8L (80:20 bark:peat with 12 lbs/yd³ Osmocote^® Plus and 8 lbs/yd³ dolomitic lime), compared to the IS (p≤0.05).  Tomatoes and bell peppers grown on the can yard and under the high tunnel had significantly greater growth and yield when grown in 4L+Ca/Mg or 8L than the C media (p≤0.05).