Michigan State University Offers Tips On Greenhouse Soil Testing
According to an article from Ron Goldy, Senior Educator with Michigan State University Extension, there are about 20 nutrients that are considered essential for plant growth. Carbon, hydrogen, and oxygen are obtained from air or water, while others are obtained from growing media, whether that is soil in the field, a hydroponic system, or something in between.
Nutrients obtained from air and water are largely beyond producer control, although in greenhouse situations CO2 levels can be enhanced, but those obtained from the growing media can, in most situations, be adjusted if needed.
Most producers are aware soil pH influences nutrient uptake. If soil pH is not within the proper range — 6.2 to 7.2 for most crops — nutrient uptake is inhibited. That doesn’t mean the nutrient is not in the soil, it just means the soil chemical environment is not suitable for uptake of that nutrient. This usually takes place in highly alkaline (greater than 7.5) or highly acidic (less than 5.5) situations.
If the pH is outside the desired range, recommendations are often made to either add sulfur to lower pH or lime to raise it. High organic soils, however, are well buffered and resistant to pH changes, so plants grown in these soils will generally need foliar applications of limiting elements. Outside the desired pH range, it is also possible for some non-essential nutrients to become more available, which can lead to nutrient toxicities. Aluminum is best known for this at lower pH.
For more information, check out Goldy’s report on the Michigan State University Extension website.