Hoophouse Nutrient Management — Notes from Great Lakes Vegetable Producer’s Network Weekly Roundtable Discussion

A few weeks ago, Great Lakes Vegetable Producer’s Network discussed hoophouse nutrient management. Judson Reid from Cornell University and David Van Eeckhout from The Good Acre, St. Paul, MN are the invited speakers. They shared their insights in hoophouse nutrient management. I find them very helpful, thus want to pass my notes to Indiana hoophouse growers.

Judson pointed two things from greenhouse perspective that may greatly benefit hoophouse growers, one is ventilation, another is pollination. Ventilation is important for managing relative humidity and maintaining carbon dioxide level. But ventilation may be sacrificed in hoophouse for the reason of maintaining temperatures during periods of cool weather. For hoophouse growers, anything that can increase ventilation (end wall vents, peak vent) could greatly benefit vegetable production in the early season. Hoophouse tomato growers can also greatly benefit from bumblebees for pollination. If the structure is usually closed and there is little wind movement of the plants, plants or flowers must be manually vibrated or visited by insects for pollination.

In terms of fertility management, Judson noted that a big change between fertility management inside hoop house and in the open field is Calcium. Vegetables grown in open field may need additions of Calcium fertilizer, but soils inside a hoophouse tend to build up Calcium when hard water with high levels of calcium carbonate is used for irrigation. Phosphorus also tends to build up in soils of hoophouses. This often occurs when composts and other fertilizers or soil amendments are applied as sources of nitrogen without attention to the amount of phosphorus that is being applied, which can be well above the amount needed or removed by the crop. A related issue is pH creep due to irrigation water high in alkalinity. Speakers gave practical ways to avoid pH creep: 1. Measure soil pH, find what pH is, one measurement in the spring, one measurement in the fall; 2. Apply sulfur on an annual basis, and include this as a standard practice if irrigation water is known to increase soil pH; 3. Acidify irrigation water if needed. Be cautious when adding acid. Test irrigation water for alkalinity and consult charts that provide guidance for the amounts of various kinds of acid to add based on the alkalinity of the water. Mixing high alkaline well water with rain water can be another approach to reducing alkalinity; 4. Remove plastic every 3-4 years and leave soil uncovered during a period with substantial precipitation. Plastic should be replaced periodically anyway because the light transmittance declines. By leaving plastic off, precipitation moves through the root zone and leaches salts and calcium; reducing salinity and pH. David pointed out that organic fertilizers are expensive, and without knowing soil pH, it is like throwing money away.

About using foliar fertilizers, speakers agree that it is a corrective action, not the main way to apply fertilizers. Foliar fertilizers may solve some immediate problems, for example, Mn (manganese) deficiency; Mn probably is enough in the soil but deficiency can occur when soil pH is too high. Foliar applied Mg (magnesium) may also have some effects, but if irrigation water is hard (alkaline) it probably contains magnesium carbonates and so magnesium is already being regularly supplied to the soil. As a corrective action, use foliar fertilizers only when a specific nutrient deficiency is known and the plant cannot obtain the nutrient from the soil.

Great Lakes Vegetable Producer’s Network is scheduled at 12:30 ET every Wednesday from the May to Sep. covering a lot of topics in vegetable production. Check the website https://www.glveg.net/listen for previous (recorded) and upcoming sessions.

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