Years ago, liming the soil was inexpensive as lime could be purchased at the local magnesium mine at Haley’s Station. But when the Haley plant closed, lime had to be trucked in from a distance. I got 216 tonnes last week and it came from near the Quebec/Vermont border in six long transports.
My farm is on a clay sea bed. It’s a nice clay soil to work with, just the odd stone here and there. But the soil needs to be limed by two or more tonnes of lime per acre at least every 10 years.
It brings some interesting questions and comments from the non-farmers, such as: Why are farmers getting their fertilizer in huge tandem loads dumped in the field?
Scientists throughout the world agree that acid soil holds back forage profits unless sweetened with lime. When needed, lime is a big crop booster that leads to equally bigger crops and thus better returns for the farmer.
Most farmers, especially dairy farmers, who grow alfalfa hay crops, know the importance of a good soil pH. Lime is the least expensive ingredient of any soil management program.
Lime is so important that some farmers list it as the fourth element along with nitrogen, phosphorus, and potassium. Of course, it isn’t an element in the true sense. But it does deserve the respect. With the ever increasing costs of other inputs, including fertilizer, one thing is for certain: liming acid soils is an absolute must for high yields and profits.
What causes soil acidity? Almost without exception where the average rainfall is more than about 25 inches per year, the soils are naturally acid. When water leaches through, the soil becomes acid, no matter if limestone itself is the parent rock from which the soil is formed. And sometimes the water itself is acid (acid rain). Also, some acids are formed when crop residues and soil organic matter decay in the soil.
Manure, ammonium nitrate, anhydrous ammonia, urea, ammonium phosphates and urea-ammonium nitrate solutions acidify the soil. It takes about three pounds of lime to neutralize one pound of N supplied by these fertilizers. And it takes five pounds of lime to neutralize the acidity of one pound N supplied by ammonium sulfate.
How does liming correct acidity? Acidity is caused by the presence of hydrogen (H) ions; pH is the measurement of the activity of these H ions. The measurement scale covers a range from 0 to 14. A pH of 7.0 means the soil in neutral; pH values below 7.0 are acid. Those above 7.0 are alkaline.
When limestone is mixed with the soil, the soil is neutralized by the action of the limestones causing it to become less acid and thus raising the pH. Although calcium and magnesium are important components of limestone, they do not change the pH. It is the carbonates that neutralize acidity.
Crops in general have a different pH requirement for optimum growth. Most forage species grow best when the soil pH is near 7.0. And most legumes, especially alfalfa and red clover, need a nearly neutral soil to promote growth of nodule-forming bacteria. If you have a field that will not grow alfalfa, the soil probably requires lime.
How often a field needs to be limed or re-limed is best determined by a soil test. Some years ago Michigan State University soil scientists estimate that from 400 to 600 pounds of lime are used up per acre each year under normal cropping conditions in that state.
