Liming no-till is no different than liming in any other tillage program except that it is less forgiving if you don’t do it right.

The key to liming in no-till is to lime on a regular basis and don’t let pH get low in the first place. If you maintain soil pH near to the optimum and don’t let it get below the 6.0-6.5 range for most crops, you can lime on the surface following a normal liming program and maintain the soil pH near the optimum without tillage.

However, if the soil pH is allowed to become very low, limestone moves very slowly down through the soil and thus it can take a very long time without mixing from tillage to neutralize the acidity even just in the plow layer. In research at Penn State on a long term no-till soil that had been left to become acid, it took 9 years to raise the pH in the plow layer (6”) from 5.1 to 6.5. There was no advantage in this research to applying limestone more frequently in no-till, it took a long time regardless.

If someone is transitioning to no-till the recommendation is that if the soil pH is very low, limestone should be applied and the soil tilled one more time to mix the lime and neutralize the acidity in the plow layer before beginning no-till. Then lime on a regular basis. If you are already in well established no-till and have neglected liming and thus have a low pH you will either have to apply limestone and live with the problem for a few years until the liming effect can move down through the soil or you may have to till to mix the limestone for more immediate reaction. If you choose to just apply the limestone on the surface, there will likely be some immediate benefit from the limestone in these low pH soils even though the full benefit may take years. This early benefit will be more likely in a well developed no-till soil with good residue management.

Acidity is constantly forming in soils in our region of the world, thus liming is an on-going management practice. For example, one of the biggest sources of acidity in ag soils is nitrogen fertilizer. Most N fertilizers create the equivalent of about 3 lb/A Calcium Carbonate Equivalent (CCE) lime requirement for each pound of N applied. For ammonium sulfate this is about 6 lb/A CCE for each pound of N applied. Thus, a 150 lb/A N application will create 450 to 900 lb/A of lime requirement per year. This is why agricultural soils in PA generally need 1-2 tons of limestone every 3 years or so. The actual amount needed will vary depending on soil properties so it is important to take a soil test to determine the actual lime requirement.

Remember that soil sampling no-till soils is different because most of the acidity, such as the N fertilizer starts at the surface. This can result in a very acid layer at the surface often called an “acid roof”. Normal plow depth soil samples can sometimes miss this acid layer. Therefore the following procedure should be followed when sampling long term no-till soils. Take a normal plow depth soil sample. If the test results call for limestone apply the recommended amount and no special sampling is required. Since the limestone will be surface applied it will automatically neutralize the acid roof first. However, if the normal soil test does not call for limestone, take a second sample from the surface inch of soil and check the pH. A simple field pH test kit can be used for this second test. If the normal test did not call for limestone but this surface pH is 6.0 or less, apply 1 ton of limestone/A.

The bottom line is never let the pH get too low in no-till. If you lime on a regular basis, usually every three years, to maintain the soil pH near to optimum and then no special management is required.

SOURCE: Doug Beegle, PSU Soil Fertility and Nutrient Management Specialist

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