In the past I have had many conversations with growers about plant nutrition in their high tunnels. A good plant nutrient management plan is an integral part of making a success of the crop you are growing. Plant nutrition is important to grow a strong and healthy seedling, the first step of a successful crop. Fertility management of especially vining crops (e.g. tomato, cucumber, peppers) are critical to achieving a good yield. It does not matter if you grow your crop in soil or in a soilless production system. Steering your crop to have the optimum balance between vegetative and reproductive growth will result in good yields over a longer period.
It is important for growers to know what is in their water and soil. Therefore, soil analysis of a representative sample of the area that will be planted, and water analysis of a water sample from the source that will be used is important. The water quality of water sources such as ponds and wells can change throughout the season. The grower might consider sampling two to three times during the growing season. This will help to manage your plant nutrient program better.
One of the big issues with well water in Indiana is that in some instances it is very alkaline. Alkalinity (as CaCO3) measures the combined amount of carbonate, bicarbonate and hydroxide ions in the water, and it describes the ability of water to neutralize acids. In other words, it buffers water against pH changes. A water that helps to buffer against pH changes is great, but a too high alkalinity will lead to an increased incidence of dripper clogging. The pH of container-grown plants tend to increase over time. Usually the optimum alkalinity range for plants is between 30 to 60 ppm (mg·L-1). Some laboratories report alkalinity in milli-equivalents (meq·L-1). Alkalinity of 50 ppm CaCO3 is equal to 1 meq·L-1. Most growers aim to have a water alkalinity of between 1.5 and 2 meq·L-1. Alkalinity can be adjusted with acid. Acid injection or the use of an acidic fertilizer can help to remedy the situation. Although, usually fertilizers with a high potential acidity do contain a high percentage of ammonical nitrogen and urea. This approach works well for container-grown plants, but be aware of ammonium toxicity under cool conditions (below 60°F). There are a few sources of acid available on the market of which sulfuric acid is very affordable and nitric acid is very caustic and has harmful fumes. Always exercise caution when working with acids, and remember always add acid to water and never water to acid. Also, take into account that the source of acid used can provide specific nutrients. Citric acid is the only source that does not supply any additional nutrients. A very useful tool to calculate how much acid is needed can be found at https://extension.unh.edu/Agric/AGGHFL/alk_calc.cfm. All you need to complete the form is the pH and alkalinity content of the water and what is your target alkalinity level.
This is the first article in a 7 part series that will look at soil fertility and nutrient solution management for high tunnels. The series will address (1) Alkalinity, (2) Water Hardness and the Removal of Unwanted Ions, (3) Water Soluble Fertilizer Calculations, (4) Fertilizer and Nutrient Solution Mixing Tips, (5) Fertilizer Injection, (6) Soil fertility, and (7) Monitoring and Diagnostic Tools.