You know soil testing is important, but do you know what to look for when the results come back? Jim Friedericks, laboratory manager at AgSource Laboratories in Ellsworth, Iowa, says even though tests are similar, they don’t always give the same results, so it’s especially important to pay attention to the details.
“Soil analysis is the most accurate, cost-effective way to optimize crop production, but when people send soil samples to laboratories for analysis, the reports may be difficult to interpret,” he says.
Friedericks says there are five aspects of a soil test in particular to which farmers should pay close attention.
1. Soil pH. The most suitable soils for field crops generally range between 6.3 to 7 pH. Soils above 7 are basic soils, while soils below 7 are acidic soils. Unbalanced pH can limit availability of phosphorous, manganese, copper, boron and zinc, Friedericks says. Liming is a good investment but a gradual process because it involves reaction between soil and lime particles.
2. Phosphorous levels. This nutrient promotes root growth and winter hardiness. When plants are deficient in phosphorous, they may appear stunted and often have an abnormal, dark-green color. Target levels in Midwest crop production is 20 to 25 ppm, Friedericks says. Soil test results are usually reported as elemental P, while fertilizer recommendations are reported as P205, he notes.
“It requires about 18 lbs of P205 to raise the soil test level by 1 ppm,” he says. “Determining the amount of fertilization needed to raise the amount of P requires calculation, and farmers should take this into consideration.”
3. Potassium levels. This nutrient aids in protein synthesis, photosynthesis and movement of water within plants, Friedericks says. Corn takes up nearly as much potassium as nitrogen in a given year, he says. It’s a great investment to protect a crop against disease because of its ability to strengthen stalks and stems against disease, he says. Thicker plant cells can make it more difficult for some diseases to invade plants during stressful periods of the growing season.
4. Organic matter. This is a key measure of soil health and structure. Although it’s hard to make immediate changes to organic matter levels, farmers should have a long-term plan for improvement in mind, Friedericks says.
“At the very least, farmers want land management to maintain or increase the organic matter content as a way to improve soil health, thus reducing crop vulnerabilities,” he says.
5. Cation Exchange Capacity (CEC). This, plus base saturation levels, help characterize soil type, Friedericks says. Together, they show how a soil can hold specific plant nutrients in the profile.
“Because there is a strong correlation between CEC values and the amount of clay and organic matter in the soil, the higher the CEC, the more soil can retain and make available moisture for plant growth,” he says.
AgSource has additional information on soil analysis and soil test reporting at www.agsource.com/laboratories.