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Publication #SL248

Soil Fertility Management for Wildlife Food Plots1

C.L. Mackowiak2

Introduction

A good seed bed is the foundation for a successful wildlife food plot. Soil fertility is an important component of seed bed preparation. At a minimum, growers should be familiar with their soil characteristics. Deep sands typically do not hold many nutrients. The heavier, red soils such as those found in the Florida Panhandle, will likely hold more nutrients when fertilized. Your local County Extension or NRCS (Natural Resources Conservation Service) office should have a soil survey book or you can go online and use the NRCS Web Soil Survey at http://websoilsurvey.nrcs.usda.gov/. The soil maps and descriptions of your property will describe soil type, inherent fertility and pH, and will guide you in choosing a plot location, thereby avoiding marginal soils.

Soil Sampling

Your next step is to sample the soil for pH and plant-available nutrients. You want to be certain that the small package of soil you send to the lab represents the soil you intend to manage for your food plots. This is best accomplished by gathering a composite soil sample.

A composite soil sample is comprised of several representative subsamples taken throughout the food plot that are combined into a single sample, using a 5-gallon bucket or a clean, non-metallic container. Metal containers may contaminate your soil sample with iron, zinc or other metals that may affect the lab results for those metals. Ten to 20 subsamples taken from the upper 6-8 inches of topsoil are used to create a composite sample. If you are unsure, take additional subsamples.

A shovel, soil probe or soil auger can be used to remove soil. To further prevent contamination, be sure the equipment is rust-free, particularly if micronutrient analysis will be conducted (Figure 1). Soil probes are fairly inexpensive and provide much more uniform core removal than shovels. Prices range from about $50 to over $200.

Figure 1. 

Examples of soil sampling options. From left, soil probe, spade, sharpshooter and soil auger.


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The most systematic method for gathering samples is subsampling at either grid centers or intersections (Figure 2). This approach is used in precision agriculture, but is less necessary for wildlife food plots. Instead, a random or zig-zag sampling pattern is acceptable. The zig-zag method has the preferable advantage over random sampling of removing some unintentional bias in selecting subsampling points (Figure 2).

If soil pH and fertility are in good standing, sampling every three years is adequate. Annual sampling may be required if fertility is sub-optimal or the food plot is located on deep sands.

Approximately two cups of a soil composite are required by an analytic laboratory. Allow your soil sample to air-dry (e.g., spread sample on a cookie sheet) before packaging it for delivery. Soils are analyzed for plant-available nutrients, not total nutrients. Moist soil samples kept in air-tight bags may undergo chemical changes, which may produce an inaccurate representation of nutrient availability in the original sample. You may send your samples to a trusted commercial lab or contact your local Extension agent for instructions on sending them to the University of Florida (UF) Extension Soils Testing Lab (ESTL), which is located on UF's campus in Gainesville.

Figure 2. 

Each example represents a 10-acre field. Each point represents a subsample.


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Soil Analyses

Laboratory analytic parameters may include soil pH, buffer pH, available NO3-N, P2O5 (phosphate), K2O (potash), Ca, Mg, Fe, Mn, Zn, Cu, B, cation exchange capacity (CEC), and percent base saturation. At a minimum, the soil should be tested for pH, buffer pH (used for calculating lime requirement), P2O5, and K2O. Nitrate-N soil values change rapidly over time; therefore, soil testing for NO3-N may not be warranted, nor is it recommended by UF/IFAS.

Percent base saturation, buffer pH, Ca and Mg values provide information relative to soil acidity and liming status. Cation exchange capacity provides an estimate of nutrient storage and release from soil particles whereby the higher the CEC value, the more fertile the soil may be. Because clays tend to hold more nutrients, the CEC provides an approximation of soil texture and vice versa. Sandy soils typically have a CEC below 12, and loamy soils typically have a CEC above 20. Soils high in CaCO3 (calcium carbonate) may have a higher CEC than their soil texture would infer. This is typically true of soils overlying marl or karst topography (i.e., limestone).

Micro or minor elements (Fe, Mn, Zn, Cu, B, Mo) are required in much lower doses than N, P, and K, and they are not measured as often. However, some Florida soils are deficient in one or more minor elements and, therefore, trace elements should be analyzed every few years, more often in very sandy soils. It is important to act cautiously when applying trace nutrients because excessive applications can harm plant growth over many years.

Soil pH/Liming

If your soil pH is above 6.0, then liming is probably not required. Without a proper soil pH, some fertilizer nutrients become less available (Figure 3), resulting in lower yields. In comparison, an acid soil (pH < 5.0) increases the risk of plant aluminum (Al) and manganese (Mn) toxicity.

Figure 3. 

Relationship between soil pH and relative plant nutrient availability (a widening bar equates to greater availability). Where nutrients are shown interlocking, they combine at that pH to form insoluble compounds that reduce phosphate solubility.


Credit:

Taken from R.W. Miller and D.T. Gardiner. Soils in Our Environment. Prentice Hall, 2001.


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It is best to incorporate the lime several months before planting your food plot. This provides time for the lime to neutralize soil acidity. Applying lime to the surface without incorporating it into the soil may limit liming effects to the upper inch or two of soil.

Not all liming materials are the same! Pure calcite is used as the standard to rank all other liming materials. Calcium carbonate equivalent (CCE) is a term used to describe relative effectiveness. If you have a material with a CCE of 70, then it will take 1.3 tons of your product to produce the same liming effect as 1.0 ton of pure calcite. Additionally, some fertilizers have either a liming or acidifying effect (negative CCE) (Table 1). Lime particle (mesh) size determines liming effectiveness or the effective neutralizing value. Rule of thumb: large lime particles (less than 20 mesh) will have minimal neutralizing value so choose smaller particle (higher mesh) sizes.

Table 1. 

Typical CCE of some liming materials.

Liming Materials

Typical CCE (%)

Calcite (pure)

100

Calcitic limestone

75 - 100

Dolomitic limestone

75 - 108

Aragonite

95 - 100

Hydrated lime (Ca(OH2)

120 - 136

Marl

50 - 90

Burned lime (CaO)

178

Flue dust

60 - 80

Wood ash

30 - 70

Basic slag

50 - 70

   

Other Materials

 

Calcium nitrate

20

Potassium nitrate

23

Rock phosphate

10

Gypsum (land plaster)

0

   

Urea

-83*

Ammonium sulfate

-110*

Diammonium phosphate

-70*

   

Humus

9

Milorganite

10

Sludges

20 - 80

*Negative values represent acidifying.

Often food plot fertility is accomplished at fall planting. Since agricultural lime requires some time to affect soil pH, pelletized lime may be used to get more rapid liming. Pelletized lime is often pulverized lime pressed into a pellet, which provides effective liming in a relatively short time. The ESTL will provide liming recommendations with your soil analysis report.

Fertilizer Recommendations

Fertilizer recommendations may be provided in either parts per million (ppm) or lbs per acre. If the analytic results are in ppm, they can be converted to lbs per acre by multiplying the values by 2. A good guide to follow for fertilization requirements of specific forages common to food plots is SL129/SS163: UF/IFAS Standardized Fertilization Recommendations for Agronomic Crops (http://edis.ifas.ufl.edu/ss163).

In addition to the UF/IFAS forage recommendations, some legumes (many clovers, alfalfa) tend to have a higher pH requirement (6.5), but there are several species, such as crimson clover and perennial peanut, that perform well in moderately acidic soils (pH 5.5 or greater). Since forage blends are frequently used, a rule of thumb is to lime to keep soil pH around 6.0. Besides being high-quality, legumes rarely need N fertilizer since they often have root associations with microorganisms that fix N, which benefits the microorganisms, the host plant, and sometimes neighboring plants, particularly as the legume is grazed, browsed, or dies.

There is plenty of anecdotal information suggesting that intermixing legumes with other forage species may reduce the need for fertilizer N. Legumes, in particular, tend to have higher S, Ca, Mg, and B requirements and, therefore, may benefit from additional fertilization with one or more of these nutrients.

To make the most use of fertilizers, follow the best management practice (BMP) of splitting the recommended fertilizer rate into two or more applications. This improves the likelihood that the plants will capture more of the fertilizer to meet their nutrient requirements. Additionally, splitting applications will lessen the economic loss from leached fertilizer and reduce the potential for surface and groundwater nutrient contamination.

Organic Fertilizers

Organic fertilizers, such as manures, litters and composts, can sometimes be used for wildlife food plots. The organic matter often improves a soil's water holding capacity and nutrient retention. The amount of available nutrients found in composts is low. Therefore, application rates may approach 20 ton/acre to meet plant nutrient requirements. In comparison, manures and litters are more nutrient-dense, so application rates are typically 5 tons/acre or less. One to 2 tons per acre is a frequent application rate.

Biosolids (AA-rated municipal sludge) are also good sources of plant nutrients. However, wildlife (deer in particular) may have an aversion to the material until it degrades and becomes incorporated into the soil. Thus, biosolids may work to protect against browsing pressure for a time, allowing for better forage establishment. To delay early encroachment by deer, application rates of around 300 lb dry biosolids/ac are all that is required. It might be advantageous to test biosolids on a small area for one or more seasons to evaluate their effectiveness as a temporary deer repellent prior to using them on larger acreage.

To learn more about specific wildlife food plot forages, see the following:

Footnotes

1.

This document is SL248, a fact sheet of the Soil and Water Science Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Publication date: March 2007. Revised May 2012. Please visit the EDIS website at http://edis.ifas.ufl.edu.

2.

C.L. Mackowiak, associate professor, Department of Soil and Water Science, North Florida Research and Education Center, Quincy, FL; Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.