Liming is not new science, back in 1760 George Washington was adding marl, a source of calcium carbonate, to his farmland as a way to “sweeten the soil.” Managing soil acidity sounds so old school but we are still using calcium carbonate to perform this soil altering function.
Current liming recommendations are more than 20 years old. They don’t reflect the economics of today’s agriculture, such as the cost of the liming product and application, and the value of the crops produced.
The Tri-State Fertility Guide recommends maintaining a pH of 6.5 for fields devoted to row crops. Over half of the soil tests we have observed recently have failed to meet the pH of 6.5 level recommendation. One point scientist agree upon is that managing soil acidity is an important component of today’s high yield agriculture.
We can spend the money to do grid sampling to tell us where we need to be putting the lime, and we now have access to variable rate equipment that can apply the material accurately, but determining exactly how much material to apply is less obvious. The basics of soil science are the same today as in Washington’s day.
Soil pH is a measure of the hydrogen ion concentration, with a pH of 7 considered neutral. As hydrogen ions increase, the soil becomes more acidic, and the pH drops. A soil with a 6.0 pH has 10 times more hydrogen ions as does a soil with a pH of 7. The single most important management step in growing corn is applying nitrogen fertilizer, which leads to a lower soil pH.
When fertilizers that contain ammonium undergo nitrification (converting the ammonia form to plant available nitrate), the chemical reaction releases hydrogen ions. Researchers have calculated that it takes 1.8 pounds of calcium carbonate to neutralize the free hydrogen ions released from every pound of nitrogen applied as Anhydrous Ammonia, Ammonium Nitrate, or Urea. Diammonium Phosphate(DAP) requires 3.6 pounds.
Ammonium Sulfate and Monoammonium Phosphate(MAP) requires 5.4 pounds of calcium carbonate to neutralize the free hydrogen ions released. In addition to neutralizing the freed hydrogen ions from the fertilizer application, today’s high yield crops remove a significant amount of basic cations that must be replaced to maintain the charge balance in the soil’s chemical system.
A 150-bushel corn crop harvested for grain requires approximately 20 pounds of ag lime per acre to replace the basic cations; a 45-bushel soybean crop requires 95 pounds of ag lime per acre to replace cations.
Total calcium carbonate required to produce a 150 bushel corn yield would be 290 pounds per acre to maintain the soil’s chemistry on an even balance. This doesn’t seem like a lot, but if we aren’t routinely soil testing to watch the pH level we could be destroying soil health and productivity.
The Carroll and Harrison Soil and Water Conservation Districts received a grant in 2013 from Muskingum Watershed Conservancy District to assist land owners in the Muskingum Watershed Conservancy District offset the cost of soil tests. The MWCD and SWCD’s felt that farmers having up to date soil test information would guide them toward proper application of lime and fertilizer. With proper fertility for the growing crops, excess nutrients would not have the opportunity to leave the site.
The crops could then utilize the available nutrients and a minimum of the nutrients would be subject to runoff into our streams, lakes and rivers. Proper soil pH assists in the soil chemical functions for weed control and nutrient uptake by the growing plants. Since liming tends to be a long term investment, extra steps should be taken to communicate with landlords. Provisions can be included in your lease that includes compensation for the lime on a three year, prorated basis if the lease is interrupted.
Soil testing should be done every three to five years, if soil test kits are needed, contact the OSU-Extension, SWCD, your agronomist, or your fertilizer dealer.