Lime’s Role in Your Field
February 05, 2013 by Bob Berkevich
The pH management of our soil is one of the most important factors for crop production. However it always seems to be overshadowed by the management of the macro-nutrients, nitrogen, phosphorus, and potassium. The reality of the situation is that an improper pH can play a major role in the availability of these nutrients. It also happens to be one of the more difficult nutrients to fix within the soil in a short time frame. That being said, the fields that need limed in 2013 need decided on right now.
Proper pH
Soil pH is a measure of soil acidity or the active hydrogen in the soil solution. A pH < 7.0 is acidic and a pH > 7.0 is alkaline. The ideal soil pH for corn and soybean production is 6.5 to 7.0. A pH of 7.0 is considered neutral. The three main contributors to increased soil acidity in our crop fields are rainfall, nitrogen fertilizers, and legumes like soybean and alfalfa.
Soils that were formed under more rainfall will typically be more acidic than soils formed in more arid conditions. Water (H20) combines with carbon dioxide (CO2) to form carbonic acid (H2CO3). When the weak acid ionizes in the soil it releases a hydrogen ion (H+). The released H+ displaces a calcium ion (Ca++), causing the soil to become more acidic.
Nitrogen fertilizers that contain or are converted to ammonium (NH4+) contribute to soil acidification. Products like anhydrous ammonia, urea, and ammonium nitrate all go through the nitrification process which basically converts ammonium to nitrate (NO3-). When this conversion takes place, hydrogen ions (H+) are released in the soil.
Crops such as soybeans use more cations such as potassium (K+) and calcium (CA++). As they take in these cations, their roots excrete H+ ions to maintain an electrochemical balance within the plant tissue, resulting in soil acidification.
Why Lime is Used
The more acidic a field becomes, the more nutrient tie up occurs, resulting in lower yields. In order to correct soil acidification, Ag lime is applied to our soils. Ag lime is used because it contains calcium carbonate (CaCo3). The more pure calcium carbonate the lime contains, the more effective it is in correcting soil pH. It is important to note that the neutralizing power of lime comes from the carbonate, not the calcium. Gypsum (CaS04) does not contain carbonate and does not alter pH. The chart below illustrates how an acidic soil can tie up fertilizers that are applied and effect fertilizer efficiency.
Tips for Liming
Any successful lime program has a process. This process involves soil sampling, building proper lime recommendations, dispatching trucks and a good spreading job with calibrated equipment. Below are a few tips that will make your liming experience as efficient as possible.
1. Grid Sample - There are very few crop production fields in the Midwest that have no variations in them. Often times the amount of money you will save on the cost of lime after grid sampling will pay for the cost of the sampling. It's smarter to put 3 ton in some areas and 1 ton in others rather than blanket applying 2 tons per acre. The maps below show a farm that was grid sampled the fall of 2011.
The map above shows the variations in pH from 5.4 to 7 and the map on the right shows the variation in lbs. of lime that would be applied from 0 to 3,000 lbs. per acre.
2. Start Planning Now - The process of liming takes much more time and preparation than fertilizing. The lime order has to pass through many different channels before it gets spread on the field. The lime spreading company, quarry, and trucking company all have to be on the same page in order to cover a large amount of acres in one lime season. When liming in the fall, try to target fields that will be harvested early. Lime will tend to freeze in the beds of trucks at temperatures below 32 degrees F. In general the drier the lime the longer you can haul in colder temperatures.
3. Not all Lime is Created Equal - Choose your lime wisely. Remember the more calcium carbonate lime contains the more effective it is on neutralizing your soil. Also, grade size can play a big part in the time it takes to raise the pH of soil. The finer the grade size, the quicker it will work. The quality of lime can differ greatly from one quarry to another. One of the best ways to find good lime is to check with those hauling and spreading the lime. They often know which quarries have the biggest supply and best quality of lime.
References
Mosaic, Efficient Fertilizer Use Manual- pH, by Dr. Cliff Snyder
