It’s that time of year! Fertilizer applications are wrapping up and lime is still being spread. We’ve been fortunate to have nice weather to allow retailers to get a lot of inputs on this fall.
Why do we need lime? In Iowa, we are extremely fortunate to have some of the best soils in the world. These rich soils come with abundant organic matter (OM). When microorganisms break down OM, they release CO2, which reacts with water to produce H+, thus producing acid and lowering soil pH. Other inputs that contain ammonia or ammonium (anhydrous ammonia, AMS, manure, etc.) can lower the pH by releasing H+ ions during the nitrification process.
Why are acidic soils bad? Ideally, we want the pH of our soils for corn and soybean production to be between 6.5-7.0. In the Des Moines lobe, we have calcareous (high pH) subsoils, so we can handle pH of even 6.0. At these ranges, nutrients are the most plant-available. Even if fertility levels are high, and the pH is low, the availability of some nutrients is limited.
Is it difficult to raise soil pH? The more clay we have in our soils, the harder it is for lime to raise the pH. The opposite is true for sandy soils. It takes less lime to neutralize sandy soils compared to a clay loam. This is factored into liming equations using the buffer pH or lime index.
What can increase soil pH? There has been a misnomer in recent years that gypsum (CaSO4) acts as either a liming agent or can lower the pH in alkaline conditions. The former is false. Gypsum does not increase pH. The latter is a little more complicated. In large amounts, it can decrease pH, but only in the right soil conditions. This is true when there is a large presence of sodium in sodic soils. Generally (thankfully), we do not typically have those conditions in Iowa. Gypsum, however, is an excellent source of Sulfur that is readily plant available and has been shown to improve soil structure in tighter or Magnesium-rich soils. Pelletized lime is becoming more popular in no-till management systems and those with the ability to apply it themselves. There are less trucking costs, and it’s easier to handle. However, it is a more expensive option. Ag lime (CaCO3) is still the most economical way to improve soil pH in Iowa.
At Labre Crop Consulting, we can help you make the right recommendation for your soil. We want you to get the most out of your fertilizer inputs, and soil testing for your lime needs can do that!
We want to wish you and your family a very Merry Christmas and a safe and happy New Year!