Understanding Soil pH
Most sportsmen realize that fertilizer is an important component in establishing or maintaining successful food plots. Yet few understand the importance of lime and soil pH in the food plot equation. In fact, lime is often the most important ingredient for creating and maintaining successful food plots.
Soil “pH” is a measure of the soil’s acidity based on a 0 to 14 point scale, with 7 being neutral. Values below 7.0 represent acidic soil and those above 7.0 indicate basic soil. An important consideration is that soil pH is measured and expressed in a logarithmic scale. This means a change in pH of one numeric unit represents a tenfold change in the sol’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.
Most soils across the whitetails’ range are acidic, and require lime applications to neutralize. Only a few isolated areas, such as portions of Alabama’s Back Belt region and some of the islands in the Mississippi River have soils naturally above neutral (basic). Acidic soils have several negative effects on food plot crop growth and nutritional value, most notably reduced microbial and insect activity. The survival and proliferation of Rhizobium bacteria, which assist legumes in fixing nitrogen are limited in acidic soil. In addition, the critical plant growth nutrients of fertilizer – phosphorus, potassium and calcium – “bond” to acidic elements, making them unavailable for plant use. Therefore, if the soil is acidic, only a portion of the fertilizer applied to a food plot will be available to the plants.
There are several reasons why soils are, or become acidic. Two common causes are related 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. Second, when forage crops are removed by deer browsing activity, the soil also 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 droppings.
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. Most universities with an agricultural school or department provide soil-testing services for a minimal fee ($4.00 - $20.00). Private laboratories specializing in soil testing are also located throughout agricultural regions of the United States. Once the laboratory analyzes your soil, they will provide you with a recommendation of how many tons per acre of lime that must be applied to neutralize the soil. Usually one or more tons of lime per acre must be applied to change the soil’s pH. Some Purina dealers also sell hand-held pH meters with remarkable accuracy.
The most common form of agricultural lime is limestone rock ground almost to the consistency of powder, which is then spread by a commercial spreader. Pelletized lime can also be purchased in 50-pound bags and spread with a seed or fertilizer broadcast spreader. Yet palletized lime costs about $200.00 per ton, while powdered lime costs only $15.00 to $35.00 per ton. Obviously powdered lime is much more economical. The frequency of soil testing and lime application depends on several factors, such as soil type. Sandy soils require more frequent lime applications than clay soils. However, clay soils will require more lime than sandy soils to produce the same change in soil pH. Lime should also be applied far ahead of planting to allow the lime to react with the soil, generally at least a month before planting. For perennial crops, timing is not as important as applying enough lime to maintain proper soil pH.
Lime is most efficient at neutralizing the soil’s pH when it has maximum contact with the soil. By tilling the soil soon after liming, soil contact can be maximized. Also, soil moisture at the time of liming is very important, since moisture is necessary for the lime’s neutralizing chemical reactions to occur.
On most hunting properties, the acreage that can be developed into food plots is limited. Therefore, from a deer herd quality point of view, it is necessary to maximize the production of nutritious forage from these limited areas. Maintaining the appropriate pH of the food plot is an essential step in accomplishing this goal.