Here is a good article by Dr Grant Woods.
Most sportsmen realize that fertilizer is an important component in establishing or maintaining successful food plots. However, rarely do I hear of sportsmen applying lime or discussing the soil's pH in reference to food plots. Actually, lime is often a more important ingredient than fertilizer in the recipe for successful food plots. In this article I'll define soil pH, describe the negative effects of acidic soil on forage crops, and describe when and how to apply lime.
What is soil “pH”? It is a measurement of the soil's acidity or basicity based on a 0 to 14 scale, where 7 is neutral. Values below 7.0 represent increasing acidity in the soil, and those above 7.0 indicate a basic soil. I'll leave the chemical definitions of acidic and basic to the classroom. For those of us who plant food plots, an important consideration is that soil pH is measured and expressed in a logarithmic scale. Practically speaking, a change in one numeric unit represents a 10–fold change in the soil’s acidity or basicity. For example, a pH of 6.0 is 10 times more acidic than a pH of 7.0, and a pH of 5.0 is 100 times more acidic than a pH of 7.0.
From my experiences establishing food plots throughout most of the whitetail's range, the only two areas I have found where the soil pH is naturally above neutral is a portion of Alabama's Black Belt region and some of the islands in the Mississippi River. I am sure there are more areas, but they are certainly the minority compared to regions with acidic soils. Therefore, I'll speak primarily about acidic soils since few will encounter basic soils.
Acidic soil is cause for concern because of several negative effects it has on food plot crop growth and nutritional value. One of the negative effects of acidic soil is reduced microbial and insect activity. For example, the survival and proliferation of Rhizobium bacteria, which assist legumes in fixing nitrogen, is limited in acidic soil.
Also, several critical nutrients for plant growth, such as phosphorus, potassium, and calcium, may be present in acidic soil, but are unavailable because they are bonded to acidic elements. These elements are usually major components of fertilizer. Therefore, only a portion of the fertilizer applied to food plots will be available to plants if the soil is acidic. The bottom line is that putting fertilizer on acidic soil is like throwing money out of your tree stand. Neither practice will attract or benefit many deer.
There are several reasons why soils are, or become acidic. Two common causes specifically relate to typical food plot situations. First, the decomposition of leaves and twigs by microorganisms produces organic acids, which in turn make the soil more acidic. Hence, food plots established in forested areas usually have very acidic soils. Secondly, when forage crops are removed by browsing, the soil often becomes more acidic. This is especially true of forages grown for deer, since many of the chemical elements in plant matter that help balance the pH are carried off and deposited elsewhere in the form of scat.
Given that soil acidity levels are so important to establishing or creating a successful food plot, it is necessary to accurately determine the soil's pH. This can easily be accomplished by collecting a soil sample as described in the summer/fall 1994 issue of Quality Whitetails (page 19) and having it analyzed. Most universities with an agricultural school or department provide soil-testing services for a minimal fee ($8 to $20). There are also private laboratories that specialize in soil testing located in agricultural regions throughout the United States.
Once the laboratory analyzes your soil, they will provide a recommendation of how many tons per acre of lime
that must be applied to establish a certain pH. I have found that some laboratories only recommend enough lime to decrease the soil acidity to 6.5. This is appropriate if you are growing small grains such as wheat and sorghum. However, my best legume crops, and food plots in general, were accomplished by adding enough lime to raise the soil's pH to 6.8–7.0. Therefore, it is best to ask the laboratory what soil pH their recommendations are designed to produce. If it is 6.5, they can tell you how much additional lime will be required to raise the pH to 7.0.
The frequency of soil testing and lime application depends on several factors, with soil type at the top of the list. All other variables being equal, to maintain soil pH, sandy soils require more frequent applications of lime than clay soils. However, clay soils will require more lime than sandy soils to produce the same change in soil pH.
The type of lime used will also affect how often it must be applied to maintain a specific soil pH. Lime composed of fine particles will rapidly alter the soil's pH, but the effect is maintained over a shorter period of time than when lime composed of coarser particles is used.
Lime is most efficient at neutralizing the soil's pH when it has maximum contact with the soil. Tilling the soil soon after lime is applied can maximize soil contact. However, lime will have little effect on soil pH if the soil is dry since moisture is necessary for the neutralizing chemical reactions to occur.
The best time of year to apply lime depends of the crops to be grown and the type of soil. Lime should be applied far enough ahead of planting to allow the lime to react with the soil. As a general rule, apply lime in the spring for fall crops, and in the fall for spring crops. For perennial crops, timing is not as important as applying enough lime to ensure the soil pH does not become too acidic.
Usually one or more tons of lime per acre are required to change the soil pH. The most common form of agricultural lime is rock ground almost to the consistency of powder. Because of the high volume required, the most efficient and convenient method of spreading lime is by hiring a commercial spreader.
For small areas, or locations where a commercial spreader cannot gain access, pelletized lime can be purchased in 50-pound bags and spread by most seed and fertilizer broadcast spreaders. To put these options in perspective, pelletized lime costs about $200 per ton plus spreading labor, while powdered lime costs only $15 to $35 per acre, including spreading, depending on the location. Obviously, powdered lime is much more economical.
On most hunting properties, the acreage that can be developed into food plots is limited. Therefore, from a herd quality point of view, it is necessary to maximize the production of nutritious forage. Maintaining the appropriate soil pH in each food plot is an essential step in accomplishing this goal.
Dr. Grant Woods is a private wildlife consultant with Woods and Associates, Inc. Grant assists landowners and hunters throughout the U.S. in improving the quality of their deer herds. He is a strong advocate of Quality Deer Management and the QDMA and a regular contributor to Quality Whitetails. Future articles by Grant will explain the relative importance of other ingredients such as nitrogen and potassium in the establishment of successful food plots for white-tailed deer.
