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Soil pH Important to Crops, Gardens


by Jeff Burbrink
Elkhart County Extension educator

Published: Friday, February 9, 2018

The following is from Jeff Burbrink, Elkhart County Extension educator.

An article I saw recently in a magazine aimed at Midwestern Corn Belt farmers touted the benefits of lime applications to fields. "Research Shows Increased Yield with Liming Treatments" was the headline.

This article, or at least the headline, bothered me. It implies that lime will solve a problem. It made an assumption that everyone's fields are all in the same condition. In our area, I know that is not true.

A few soil chemistry basics first: Soil pH is a measure of the acidity or alkalinity of the soil. It is measured on a scale from 0 to 14. From 0 to 7 is acidic. From 7 to 14 is alkaline. Some people use the term sour to describe acidic (think lemons). Sweet is another common term to describe alkaline (or basic) soil pH. A pH of 7, half way between 0 and 14, is neutral.

The corn and soybean crops we grow in Elkhart County, as well as most of our vegetables, prefer a soil pH that is slightly acidic, say 6.2 to 7.0. In that range, the major nutrients needed by these plants are available to the plants' root systems. At pH outside of that optimal range, some nutrients are tied up by the chemistry in the soil, and the plant cannot extract them.

A good example of this is pin oak trees. Plant a pin oak in a soil with a pH higher than 7.3, and you will watch the tree leaves slowly turn yellow from lack of iron, or manganese or both. The tree will live, but it will not thrive. Generally speaking, if you plant a pin oak on the sandy soils in Elkhart County, you will probably see this happen in your own yard, because the pH is too high on most of those soils for a pin oak.

Lime is used to correct a pH on an acid soil. The calcium in the ground up limestone neutralizes acid. By adding lime to a soil with a pH of 5.5 or 6, you would expect to see the pH rise.

But what if the pH is above 7, say a 7.5 or a 7.8? Judging by all the soil tests that go across my desk each year, having a high pH is more the norm in our community than the exception. Putting lime on might only intensify problems if the pH is out of the range your plants require. In fact, every year I see lawns that people have treated with lime because "something was wrong" and it only made the problem worse.

To correct a high soil pH issue, the solution is to apply some sulfur. The amount of sulfur to apply depends on several factors: the starting pH, the type of soil (sandy, loamy, clay) and the target pH you are trying to reach.

You cannot guess how much sulfur to apply to your field, or garden or your lawn. Nor can you guess how much lime to apply. That is why you'll see Extension Educators and Specialists repeating over and over that it is important to soil test fields and gardens every 3 to 5 years. A basic soil test measures pH, as well as a few key nutrients like phosphorus and potassium.

Yes, there are fields in our area that need lime to correct low pH issues. There are many fields and gardens that are alkaline and would benefit from some sulfur to lower the pH. Testing, not guessing, can answer many questions.

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