Nutrient Management and Budgets In High Tunnels

Proper nutrient management is essential for optimizing yield and quality in a high tunnel system.  Because the season is extended and conditions less stressful, the yield potential of vegetables in a high tunnel system is generally higher than in open field production.  This is especially the case in cold climate regions of the U.S. such as Minnesota.  As yield potential increases, the need for nutrients also increase.  Lack of nutrients may cause nutrient deficiencies, while excessive application can result in salt accumulation.  Both situations can negatively affect yield and quality.  In order to obtain a better understanding of the nutrient uptake capacity of high tunnel-grown vegetables, a study was conducted using tomato (Lycopersicon esculentum cv. Sunshine) and cucumber (Cucumis sativus cv. Sweet Success) in a high tunnel in Staples, MN.  The native soil is a Verndale sandy loam and was amended with 4 inches of yard waste/manure-based compost in the fall prior to planting the following spring.  Soil samples were collected before planting and following final harvest to a depth of two feet.  Both tomatoes and cucumbers were planted in double rows in beds spaced 4 ft apart.  Within bed spacing was 18 inches between plants in staggered rows. Plants were irrigated with a drip tape system installed beneath plastic mulch.  Because of high soil test potassium and phosphorus, only nitrogen, as either urea-ammonium nitrate (UAN, 28% N) or calcium nitrate (CAN, 15.5% N), was applied using a batch fertigation system.  Three, nine foot sections (each section containing six plants) of each vegetable were monitored for yield and nutrient uptake. Tomato and cucumber plants were pruned periodically to promote upright growth.  All pruned material was weighed fresh and then dried.  Harvest of tomatoes started on July 15 and continued at periodic intervals until October 7.  Cucumber harvest started on June 28 and continued until October 19. Fresh weight yields were recorded and subsamples were collected periodically to determine fruit dry matter percentage.  At the final harvest, all remaining above ground shoots and leaves were weighed and then dried.  Dried samples of pruned material, vines, and fruit were ground and then analyzed for nutrient concentrations and nutrient uptake calculated.  A nutrient budget for each crop will be presented.