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Correcting soil pH
Dr. Victor Martin

The drought monitor report as of April 9 is showing conditions moving from no dryness to abnormally dry for much of Southwest Kansas and we are still mostly abnormally dry. Moderate drought is expanding in the central part of the state. The six to ten-day outlook (April 17 to 21) indicates leaning to slightly below normal temperatures and a 33 to 40% chance of leaning to above normal precipitation. The eight to 14-day outlook (April 19 to 25) indicates near normal for temperatures and a continued 33 to 40% leaning above normal for precipitation.  

Last week’s column discussed the possible negative effects of soil pH with low (acid) and high (alkaline) pH for our common crops. Our crops, and beneficial soil organisms prefer a soil pH of approximately 6.2 to 7.2, slight acid to very slightly alkaline.  Today, what can be done to cope with soil pH when it’s out of that range.

Let’s deal with high pH, alkaline soils first. Typically, as long as the soil doesn’t have a high salt content and it’s under 8.5, we typically don’t worry much. Occasionally at a pH of 8, but typically higher, we may see crops such as soybeans exhibit an iron deficiency, especially is parts of Southwest Kansas. You can try to apply iron as a foliar spray but it can potentially damage the crop, isn’t cheap, and may or may not work. The better suggestion is to plant more tolerant crops. At high pH, there are applications to lower pH such as elemental sulfur or even sulfuric acid. However, these are extremely expensive and impractical on a crop field basis. It may be practical for a small area such as a flower bed for acid loving flowering plants or even with certain crops like blueberries. A problem you should correct is a combination of high soil pH with high salt content. Here the most practical option is calcium sulfate, gypsum. The calcium can displace the sodium and allow it leach with rainfall or irrigation below the root zone.

Acid soils are more practical to correct. Acid soils in our area are more likely found on the sandy soils of our region, in South Central Kansas, and especially Southeast Kansas. You may find acid soils in North Central and Northeast Kansas but typically not to as great an extent.  

There are several products to raise soil pH but the most common and practical is calcitic limestone, Ag Lime. Dolomitic lime, which contains both calcium and magnesium carbonate is also an option. The amount you will need is a function of soil type, organic matter content, and the actual pH. If a soil test indicates acid soil conditions, a Lime Test Index, will tell you how much you need. Heavier, higher clay content soils, require more than lighter sandier soils but require liming less often. Higher organic matter content also increases the amount of lime needed. There are other factors such as the purity and fineness of the material that matter. The key is Ag lime is crushed rock and take time to work. It needs incorporation and moisture to raise soil pH.

Finally, if you can’t lime for whatever reason, there are some cheats. For wheat farmers, you can select an acid tolerant variety. And adding phosphorus in the row at planting can help.

Dr. Victor L. Martin is the agriculture instructor/coordinator for Barton Community College. He can be reached at 620-792-9207, ext. 207, or