Determining Optimum Calcium and Magnesium Sources and Rates for Home Gardeners Growing Vegetables in Potting Media Using Alkaline Irrigation Water

Home gardeners living in areas with alkaline water sources do not have easy or economically affordable means of acidifying irrigation water for vegetable production. One solution for achieving optimal vegetable yields using alkaline irrigation water is to grow the vegetables in a modified medium. To date, no medium on the retail market suits such growing needs. Therefore, medium recipes with varied levels (0, 4, or 8 lb/yard 3 ) and sources of calcium [dolomitic lime, calcium sulfate (CaSO 4 )] and magnesium [dolomitic lime, magnesium sulfate (MgSO 4 )] were tested using an alkaline irrigation on ‘Oakleaf’ lettuce ( Lactuca sativa ), ‘Earliana’ and ‘Salad Delight’ cabbage ( Brassica oleracea var. capitata ), and ‘Snow Crown’ cauliflower ( Brassica oleracea var. botrytis ) crops. Additionally, crops were grown in two environments, under a high tunnel and on a nursery yard. High tunnel and nursery yard sites were used to test media performances in the presence of, and eliminating, rainwater to simulate container-grown vegetables growing in both a home garden situation and a commercial greenhouse production situation. The base mix of all media treatments in the study was 80 bark : 20 peat and fertilized with 12 lb/yard 3 slow-release fertilizer at a rate of 1.8 lb/yard 3 nitrogen (N), 0.5 lb/yard 3 phosphorus (P), and 1 lb/yard 3 potassium (K). This initial fertilizer application was incorporated to each medium before filling containers. Four treatments were tested against a commercially available medium, industry standard (IS) treatment (a commercially available bagged medium), and a control medium [treatment C (no supplemental calcium or magnesium fertilizer)] by supplementing the base mix with the following fertilizer levels: 4 lb/yard 3 each of CaSO 4 and MgSO 4 (treatment 1); 4 lb/yard 3 dolomitic lime (treatment 2); 4 lb/yard 3 each of dolomitic lime, CaSO 4 , and MgSO 4 (treatment 3); 8 lb/yard 3 dolomitic lime (treatment 4). Media treatments 1 through 4 outperformed the IS and C media treatments in nearly all crops. All crops grown on the nursery yard, and cabbage grown under the high tunnel, had greater yields when grown in medium treatment 3, compared with the IS and C media treatments ( P ≤ 0.05). All crops grown in medium treatment 2 on the nursery yard produced greater yields than the IS and C media treatments ( P ≤ 0.05).