By Scout Nelson
Saturated media extract testing, often called SME testing, is becoming more common in high tunnel vegetable production. The method was originally developed for greenhouse potting media and soilless growing systems. Researchers are now studying how useful it may be for high tunnel soils.
In a standard soil test, special chemical solutions are used to measure nutrients available in the soil throughout the growing season. These tests are designed for field soils that contain mineral particles, organic matter, water, and air. In contrast, SME testing simply mixes water into the soil, filters the liquid, and measures nutrients found in that solution.
Greenhouse potting mixes usually contain peat, bark, coconut coir, and perlite. These materials have low buffering capacity, meaning they cannot hold nutrients for long periods. Because of this, greenhouse growers often fertigate crops weekly and use SME testing to monitor nutrient levels closely.
High tunnel soils, however, are more like field soils than greenhouse media. Although they often contain high organic matter and use drip irrigation systems, their root zones are much larger than those in containers. Experts say high tunnel soils still behave more like traditional agricultural soils.
Researchers explain that SME testing is most useful for measuring nutrients available at a specific moment. It can help detect excess ammonium, boron toxicity, salt buildup, soil pH, and nitrate levels. Some growers may also use the test to guide early fertilizer applications.
However, experts warn that SME testing should not replace regular soil testing for long-term fertility planning. The test does not properly measure soil buffering capacity, which is important for nutrients like calcium, magnesium, and potassium. It also does not accurately estimate phosphorus availability because phosphorus is not easily dissolved in soil water.
Specialists recommend continuing to use regular soil tests with high tunnel fertility guidelines. Foliar testing can also provide a better understanding of how plants absorb nutrients. Proper irrigation, multiple drip lines, and careful organic matter management are also important for maintaining healthy high tunnel soils and preventing nutrient problems over time.
Photo Credit: gettyimages-casarsaguru
Categories: Minnesota, Crops, General