Fixing Your Soil When Soil Is Too Acidic

By: Heather Rhoades

Many gardens start out as great ideas only to find that things don’t grow quite as planned. This could very well be because the soil is too acidic to support the life of some plants. What causes acid soil? There are many things that can cause the soil to be too acidic.

Effect of Acid Soils on Plant Growth

Sometimes there could be too much aluminum in the soil, making it acidic. Sometimes there is too much manganese, which is toxic to plants. If the soil is too acidic, it can be because of a calcium and magnesium deficiency, which is just as bad for plants as it is for humans. Iron and aluminum in great amounts can tie up phosphorus, which also makes the soil too acidic for plants.

Another thing to consider if your soil is too acidic is poor bacterial growth. This is because with bacteria, the soil becomes more alkaline, and if there isn’t enough of the good bacteria, your soil will not be fertile enough to support life.

So what causes acid soil? Many things can do it, from natural soil pH to the types of mulch you use. Acidic soil can have mineral deficiencies just like the human body, and unless these deficiencies are fixed, the plants won’t live. So if your soil is too acidic, you’ll need to correct it.

How to Lower Acid Amount in Soil

The most common way to raise the pH of soil is to add pulverized limestone to the soil. Limestone acts as a soil acid neutralizer and consists of either calcium and magnesium carbonate or calcium carbonate. These are called dolomitic limestone and calcitic limestone respectively.

The first thing that needs to be done is a soil test to see how acidic the soil actually is. You want your soil pH to be around 7.0, or neutral. Once you have run the soil test and have the results, you will know which kind of pulverized limestone to add as a soil acid neutralizer.

Once you know the kind of soil acid neutralizer to add to your soil, apply the lime according to the instructions given to you by the garden center. Never apply more than necessary.

Making sure you know what causes acid soil is important, but be careful not to add too much limestone in your efforts to correct it. If you end up with alkaline soil, you could have other problems like iron, manganese and zinc deficiencies, which also won’t support life. Further, you could end up with an overgrowth of bacteria in the soil, which can kill those things that spend a long time underground, like potatoes.

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Soil Acidity and Liming: Basic Information for Farmers and Gardeners SoilFacts

Nearly all North Carolina soils are naturally acidic and need lime, which neutralizes the acidity, for optimum growth of crops, forages, turf, trees, and many ornamentals. Even though most of these soils have been limed in the past, periodic additions of lime based on soil tests are still needed. Soil-test summaries and field records compiled by the North Carolina Department of Agriculture & Consumer Services (NCDA&CS) emphasize that poor management of soil pH accounts for a high percentage of the “crop problems” in North Carolina.

Factors Affecting Soil pH

The pH value of a soil is influenced by the kinds of parent materials from which the soil was formed. Soils developed from basic rocks generally have higher pH values than those formed from acid rocks.

Rainfall also affects soil pH. Water passing through the soil leaches basic nutrients such as calcium and magnesium from the soil. They are replaced by acidic elements such as aluminum and iron. For this reason, soils formed under high rainfall conditions are more acidic than those formed under arid (dry) conditions.

Application of fertilizers containing ammonium or urea speeds up the rate at which acidity develops. The decomposition of organic matter also adds to soil acidity.

Muriatic Acid and Soil

Like any acidic substance, muriatic acid can technically be used to neutralize soil, if you use enough of it. However, it is not generally a good option because of how caustic it is. When put into the soil, muriatic acid does not necessarily degrade very much. Although it may evaporate from the surface of the soil, a lot of it will stay in the ground and eventually leach into the water supply, which is harmful to wildlife and aquatic organisms. Some of the muriatic acid may break down on contact with alkaline substances, but the acidifying or neutralizing effect it may have is neither reliable nor safe.

Soil Acidification: How to Lower Soil pH

Many plant species require acid soil conditions to thrive. Throughout Ohio and many other parts of the Midwest surface soils are neutral to slightly alkaline. Elemental sulfur can be applied as a soil amendment to decrease the pH or acidify such soils. Due to the cost, the application of sulfur to acidify soils is more practical for horticultural crops than agronomic crops. The objective of this fact sheet is to provide interested individuals (agronomic and horticultural) with rates necessary to adjust soil pH.

Sulfur reaction in the soil is slow, and quick changes in soil pH should not be expected. It may take a few months or longer to change soil pH to the desired level because the process of sulfur oxidation (conversion of elemental sulfur to sulfate) is the result of microbial activity. Elemental sulfur should be incorporated to increase the speed of oxidation. Since the oxidation of sulfur is the result of microbial activity, fall and winter applications are not advisable (it can be done but changes in soil pH will not occur). Equation 1 shows the chemical process by which sulfur (S) application results in release of hydrogen ions (H + ) to change soil pH:

Equation 1: CO2 + S 0 + ½O2 + 2H2O —> CH2O + SO4 2- + 2H +

Addition of elemental sulfur to soil produces two hydrogen ions, which can be seen from Equation 1 (Havlin et al., 1999). The hydrogen ions released cause soil pH to decrease. Soil pH is, after all, simply a measure of the hydrogen ion concentration in soil solution, and the higher the concentration, the lower the soil pH.

If the soil is calcareous (contains free calcium carbonate), additional sulfur will be required to neutralize the free calcium carbonate. To neutralize a soil that contains 2% calcium carbonate, for example, requires 6 tons of sulfur per acre (this only neutralizes the calcium carbonate additional sulfur will be needed to affect a change in soil pH). Obviously, it would be impractical to apply enough elemental sulfur to alter soil pH of calcareous soils on a field scale. Soils of Eastern Ohio typically do not contain free calcium carbonate, but there are soils in Western Ohio that do. Assuming there is no free calcium carbonate, the amount of elemental sulfur needed to lower soil pH is given in Table 1. Note that the amount of sulfur required to lower soil pH varies depending upon soil texture.

To convert the recommended rates from pounds per acre to pounds per 1000 ft 2 divide the values in Table 1 by 43.56. To adjust the pH of a soil with a measurable volume, use Equation 2 to determine the rate of sulfur needed:

Equation 2: Calculated rate (lb/volume) = sulfur recommendation (lb/A) ÷ 37,635,722 x soil volume (in 3 )

Table 1. Rates of elemental sulfur required to decrease soil pH to a depth of 6 inches.
Desired change in pH Application rate based on soil texture 1
Sand Silt loam Clay
----------------------- lb S/A ----------------------
8.5 to 6.5 370 730 1460
8.0 to 6.5 340 670 1340
7.5 to 6.5 300 600 1200
7.0 to 6.5 180 360 720
8.5 to 5.5 830 1660 3310
8.0 to 5.5 800 1600 3190
7.5 to 5.5 760 1530 3050
7.0 to 5.5 640 1290 2580
1 Assumptions—cation exchange capacity of the sandy loam, silt loam, and clay soil are 5, 10 and 20 meq/100 g, respectively soils are not calcareous.

When using Equation 2, the sulfur recommendation is determined from Table 1, and soil volume is the volume (in cubic inches) of soil in the container. If acidifying the entire volume of soil (which may be possible if the container is small enough), mix the sulfur with the soil thoroughly. If the sulfur cannot be adequately mixed with the entire volume of soil, then determine the area of the container (in square inches – width * length) and determine to what depth the sulfur can be incorporated (measurement in inches). Calculate the volume of soil (in 3 ) and use Equation 2 to determine the new sulfur rate. For example, if attempting to acidify soil in a container that is 36 inches in diameter to a depth of 8 inches and the recommended rate of sulfur (based on initial soil pH) is 360 lb sulfur per acre, it would require 0.08 lb of sulfur be mixed with the top 8 inches of soil (360 ÷ 37,635,722 x 8143). For a deep rooted crop this may not acidify the entire volume of soil, so multiple applications over time will probably be necessary. Remember, soil pH adjustment will not happen quickly, so give the material time to react.

Soil pH adjustments with elemental sulfur should be monitored over time with routine soil sampling and analysis. This will ensure that the sulfur applied is having the desired effect on soil pH. Soils that are overacidified due to sulfur application (soil pH is lower than desired) should be limed to neutralize soil pH to the desired soil pH level. Soils that are underacidified (soil pH is higher than desired) should receive additional sulfur. Once the soil pH has been acidified to the desired level, the soil pH should remain low for a fairly long period (greater than 5 years). It may not be definite, so monitoring of soil pH with soil sampling is important.

Calibration and why accuracy went out the window quickly

There’s a 6.86 and 4.01 pH packet that you’re supposed to use to calibrate. Add the 6.86 to 250mL (a cup) of water, mix it up, stick the meter in a little and adjust the screw. Then do the same with the 4.01 pH packet with a new cup of water.

I did this with distilled water and had the same issue that others have run into: You could calibrate it at 6.86, but then it was a little off at 4.01 (showed 4.10). Calibrate at 4.01 and it’s off at 6.86 (showed 6.65).

Since plants usually tolerate wide pH ranges like 5.5-7.0, this wasn’t a huge deal for me. As long as I’m not at the min/max, it’s not the end of the world if I’m off by 0.1 or 0.2.

Neutralize Pine Needle Acid In Soil

Send a soil sample to a local extension service to determine the pH of the soil, and how much you may need to increase it and what other nutrients you may need to add to the soil. Purchase a pH-raising material. Hydrated lime will have a rapid effect on pH without the added nitrogen. Calculate the area of ground to be covered. For a square or rectangular plot of ground area is length times width.

Wear a breathing mask when spreading lime.

Consult with your local nursery to determine the best shade-tolerant grass for your area.

Watch the video: How to Adjust pH of soil EasilyHow to Adjust Alkalinity n Acidity of soil easily

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