Now is the time to find out what shape your pastures are in.
Dr. John Jennings, University of Arkansas Extension forage specialist, told Ozarks Farm & Neighbor it’s a good idea to conduct soil sampling in the fall. “You usually have moisture so you can get a good sample, especially on rocky or hard soil,” he explained. “Also, you can get results back before the big rush in late winter or early spring, so you have your results in time to be able to make adjustments in fertility amendments for spring forage production.”
Even if you can’t fertilize every field, Jennings said it’s valuable to know what the fertility levels are. But he’s worried about a problem that’s been building over the last 5 to 10 years. “Producers are letting their soil potash levels drop way down,” Jennings said. “Potash fertilizer has really increased in price, so a lot of producers have cut back on the applications they’ve been making. When the potash level in the soil drops down too low, the forage production goes along with it,” adding if yields crash and fields become unproductive as a result of low potash, it takes a while to catch up.
In most cases, producers don’t need to incorporate the fertilizers they apply into the soil. An exception is when preparing a seed bed for a new establishment; Jennings said in that case it’s a good idea, because disking all of the inputs into the seed bed gets them down into the root zone and helps the seedlings develop a good, strong root system.”
Another deficiency that can be detected via soil test is acidity; if the pH of the soil is too low, an application of lime is called for. Jennings said a low pH will stall productivity, particularly of legumes like clovers and alfalfa, which need a higher pH than typical grasses. Tim Schnakenberg, University of Missouri Extension agronomy specialist for the Southwest Region, recommended keeping the pH in the 6.0-6.5 range. He told OFN, “If you have a piece of ground that was never limed, maybe just grew grass or trees for timber, usually the pH is going to be somewhere from 4.5-5.0. When you have a pH at that level it’ll grow things, but it may not grow them as well as if the pH was elevated. The limestone will react to the soil and adjust that pH, and it makes more nutrients available that are already in the soil but are tied up and can’t be utilized by the plant roots.”
In addition to testing for soil acidity and for the key nutrients phosphorus and potassium, producers can also test soil for magnesium, calcium and even micronutrients, although Schnakenberg said in most instances they’re already at satisfactory levels. Although the soil test will yield recommendations for nitrogen as well, forage producers don’t test for N. Schnakenberg said, “It’s really pointless to test for nitrogen, because it is a very mobile nutrient in the soil and doesn’t stay put very long. You can test it today and get a number, but that doesn’t mean it’s the same in a month. It’s not as stable as the other elements are.”
He recommended getting the lime applied as soon as possible, because it can take six months to a year before it starts adjusting the pH. It’s also helpful to apply phosphorus and potassium in the fall; that gives it all winter to break down and move into the soil profile, where it’s available for next year’s growth. Nitrogen, on the other hand, will volatize, and fall applications are not recommended. Soil nutrients are very stable, and frequent testing is not necessary; Schnakenberg said every 3-4 years will do, provided it’s done well. He said, “We like to recommend going down and probing the soil, either with an auger or a soil probe, 10-20 different places. When you do that in random areas that are representative of the field, you can be confident that you’ve taken a lot of variability out of the field.”
