There are a lot of questions and comments about liming soil and how best to correct pH. Some folks feel that pelletized lime is best, some say ag lime is the way to go. There are liquid products sold in jugs to spray on your plots. I think there is a lot of misinformation out there so I thought I would do some research and draw from my own experience and explain what you should know about the what, why and how of correcting soil pH.
PH is the most important soil parameter to get right. Nothing else matters if pH is way off. A nearly neutral pH is where your soil needs to be to grow most plants we want in food plots. To get there, we can apply a wide variety of substances and methods. The very best and least expensive is to have a spreader truck deliver pulverized lime from a limestone quarry and spread it for you. But that is not the only answer. For more details, read on.
Soil pH Definition
Before we can correct your soil pH we need to understand what it is. What is pH anyway? PH, for us non-chemists, is the activity of Hydrogen ions in the soil solution. Different things cause this situation and we will get into that a little later. But that’s all it really is. On the other side of neutral, the alkaline side, is the activity of hydroxide molecules.
The pH scale
I think everyone reading this knows that the pH scale goes from 1 to 14. It is a log base ten scale, so every increment is ten times different than the next. A pH of 7 is neutral, so there is essentially no H+ or OH- molecules active in the soil solution. Most soils have a pH of 5.5 to 7.5. In the Northeast forested region, our soils are generally in the high 5s. Too acidic for most food plot plants. A good pH for food plots is 6.4 to 6.8.
What Causes Acidic Soil
Several natural factors and man-made factors affect pH. Parent materials like sandstone and shale are naturally acidic while limestone soils are neutral. In Pennsylvania, the farms, at least the productive ones are located in the limestone valleys while the mountains and rolling shaley hills are better off in timber cover. Forest soils are acidic because of the parent material as well as another cause – rotting vegetation.
A man made cause of acidity is overuse of nitrogen fertilizer. Folks often figure that if a little fertilizer is good, a lot is better. And for some reason people often apply fertilizer without a soil test. Nitrogen, if it isn’t taken up by a plant breaks down into nitrate (pollution) and Hydrogen ions (acidity.) When plants take up nitrogen, the root give off OH- ions to maintain a neutral electrical balance, and when the plant dies, organic material goes back to feeding other plant roots and soil biota. [This is one of the reasons we want to keep a cover crop on the ground all year.] Remember that too many H+ ions make the soil acidic.
Effects of Soil Acidity
When pH gets really low, like below 5, aluminum and manganese mobilize in the soil at toxic levels. Also, necessary nutrient elements become much less available in the soil solution. Therefor, the pH must be corrected before fertilizer does any good. What happens is that H+ ions take up exchange sites of the soil particles, displacing nutrient ions so the nutrients are not able to get to the plant tissues as needed, even if they are present in the soil. The main takeaway here is that soil nutrients cannot get into the plants if the pH is low and most nutrients are mobile and available to the plant at a pH close to neutral but a little below. Most plants thrive in this pH range.
How to Correct Soil Acidity
There are many materials the can be used to correct soil pH. I have used paper pulp sludge, sewage treatment plant compost, ground sea shells, dolomite, slag, agricultural lime, pulverized lime, pelletized lime and hydrated lime. The most common soil additive to sweeten or neutralize soil is limestone. Limestone is mostly calcium carbonate. Calcium carbonate is CaCO3. Remember that acidity is H+ molecules. CaCO3 reacts with H to form CO2 and H2O. Calcium ions then take the place of Hydrogen on the soil particles. We then have the added benefit of an important nutrient, calcium, which is used in great quantities by plants to build cell walls and in the biological functions. Also, when calcium molecules are bonded to soil particles, it can easily exchange its bond site with other positively charged nutrient ions, or cations. These include sodium, magnesium, ammonium and potassium.
What Type of Lime is Best
There is a lot of argument about what type of lime is better. There really is no best type, it really depends on the situation. If you need a to move the pH a long way, for instance you have a pH reading of 5.5 and you need several tons of lime per acre. There is only one choice and that’s a delivery of pulverized limestone. You can get ten tons spread for somewhere in the neighborhood of $500 with no effort. For small jobs in remote food plots, spreading pelletized lime, which is pulverized limestone mixed with clay and pressed into pellets for easy handling. This is very labor intensive and expensive. You can also get ag lime and rent a chain spreader and pull it behind a truck or tractor. Not as quick acting as pulverized limestone but you can get a lot on the field anywhere you can get your truck. Here is a link to a video about that: https://www.youtube.com/edit?o=U&video_id=TykS3_eugIc
If your soil test shows you need magnesium, you can get dolomitic limestone which has some magnesium carbonate along with calcium carbonate to increase magnesium levels at the same time as raising pH levels. If you have a very low soil organic matter (well below 5%) you can possibly find lime-stabilized compost at a nearby sewage treatment facility. This is some good stuff that will solve a lot of soil problems and it is very cheap to buy. You can discuss the analysis of the material with the staff. A lot of people have a problem with the idea of spreading sewage on their field but I assure you its very clean and safe and is very environmentally friendly thing to recycle rather than throw it in a landfill. All sludge should go back to the soil to complete the nutrient cycle. Paper mill sludges can have the same positive effects of increased organic matter and pH. I have seen situations where one can obtain this material for free as it has to be hauled to a landfill and it would be far cheaper for the mill to bring it to your field.
Well, there are some simplified explanations of how pH effects your soil and its ability to grow deer food plots and how to correct acid soil conditions. There are a couple more details you should be aware of. One is that calcium doesn’t move very far in the soil quickly, so it is a good idea to incorporate the lime into the root zone with disking. This is the only time I recommend tillage – when heavy applications of amendments are done.
How Often Should I Lime?
Once pH is straightened out, and you grow a rotation of cover crops as recommended in other articles, you should have many years of good pH levels without having to amend the soil again. Plants and corrected mineral levels will keep the soil at a good level within its own healthy ecosystem.
If a crop is taken off every year, you loose the nutrient ions that were attached to soil and were used by the plant. If you apply herbicide and fertilizer, you are applying salt chemicals that will acidify soil. The texture of the soil helps buffer acidification. When there is a large clay component with a high Cation Exchange Capacity, then there is a larger reservoir of cations that need changed so your current pH is buffered. Clay soil is harder to get a change, takes longer.
