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Soil pH
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With the growing season over, it’s time to put your feet up and relax, right? There are no weeds to pull, or watering to be done. The harvest is in, and now it’s time to enjoy a little down time. Well, maybe not just yet. There is still some time to treat your soils and do a little preparation for next spring. In Barton County, we have a pretty high Ph. We can’t be sure what your soil Ph is without a soil test. The range for most of this area is from 7.1 all the way up to 8.3, this may cause iron chlorosis. Soils in Barton County normally contain adequate amounts of iron, but a high pH makes that iron unavailable to the plant.
Iron plays a major role in the production of chlorophyll. Thus, a lack of iron reduces the amount of chlorophyll and results in yellowing of leaves. Iron chlorosis weakens, and in severe cases, may kill a susceptible plant. A popular recommendation for high pH soils is adding sulfur in order to lower pH. This works well for many soils, but not those that are calcareous.
Calcareous soils are those that contain actual particles of calcium carbonate (limestone). For part of our county, we have a base rock of limestone, so this can be a concern. How can you tell? Perform this simple test to see if your soil contains appreciable amounts of free lime. Apply one drop of vinegar to dry soil. A vigorous fizz usually means the soil contains at least 3 percent calcium carbonate. A mild fizz suggests a calcium carbonate of between 1 and 2 percent and a fizz that can only be heard suggests the soil has a calcium carbonate content less than 1 percent.
Calcareous soils can be difficult to practically impossible to acidify because the sulfur must neutralize all the free limestone before the pH is affected long term. In many cases you would need well over a pound of sulfur per square foot just to neutralize the free lime. So what do you do? That depends on the situation. With vegetable gardens and annual flowerbeds, work products into the soil during the time of year when there are no plants present. Oregon State University suggests mixing 5 pounds of sulfur per 100 square feet into the soil before planting. The idea is to form little pockets of acidity that result in enough iron availability for the plants during the year of application. Note that this must be done each year.
Another possibility is to use iron chelates. Iron chelates hold the iron in such a way that the plant can get to it. However, not all iron chelates will work in high pH soils. For soils with a pH over 7.2, use a chelate that contains FeEDDHA (iron ethylenediamine-di- (ohydroxyphenylacetate)). This can be found in the products Sequestar 6% Iron Chelate WDG, Sequestrene 138 and MillersFerriPlus. Chelates can either be mixed into the soil at planting or sprayed on the foliage early in the season and should be reappied as needed.
Alicia Boor is the Agriculture and Natural Resources agent for Barton County K-State Research and Extension. You can contact her by e-mail at or calling 620-793-1910