Soil and Fertilizer Management Considerations for Forage Systems in Georgia (B 1346) University of Georgia Extension Georgia possesses diverse soil conditions and many forage production factors are influenced by this diversity. As a result, the soil environment of a given site must be considered when selecting forage species, determining fertilization strategies and planning forage utilization systems. This article guides forage producers through the process of exploring their soil's characteristics and sampling the soil in pastures and hayfields for testing, and provides information about specific nutrients and soil amendments relative to forage production practices. Recommendations are also made on how to minimize the economic and environmental risks associated with the addition of nutrients to pasture and hayfields. 2014-12-03 16:38:18.997 2008-11-17 16:54:05.0 Soil and Fertilizer Management Considerations for Forage Systems in Georgia | Publications | UGA Extension Skip to content

Soil and Fertilizer Management Considerations for Forage Systems in Georgia (B 1346)

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Cows grazing

Dennis W. Hancock, Extension Agronomist - Forage Crops, Crop & Soil Sciences Dept.
Glen H. Harris, Extension Agronomist - Soils and Fertilizer, Crop & Soil Sciences Dept.
Randy W. Franks, County Extension Coordinator, Wayne County
Steven P. Morgan, County Extension Coordinator, Harris County
T. Wade Green, County Extension Coordinator, Twiggs County

Exploring a Soil’s Characteristics

When designing a forage management system, it is important to understand the soil environment of the site. There are four levels or scales that must be considered when developing a management plan for a specific site: the geographic region, soil province, soil types, and site-specific conditions (Figure 1).

Forage Management Decision Flow ChartFigure 1. Forage management decisions are affected by soil characteristics on four basic scales.

Georgia's geographic regions and soil provinces maps

Geographic Regions in Georgia

Essentially, Georgia can be thought of as having three main geographic regions: 1) the Limestone Valley/Mountains Region, 2) the Piedmont Region and 3) the Coastal Plain Region (Figure 2). Some forage management recommendations are based on these regional breakdowns. The two most notable examples of recommendations based on region are planting dates1 and variety recommendations2. These region-specific recommendations are primarily the result of climatic differences from one region to another rather than differences in soil characteristics.

Soil Provinces in Georgia

It is often helpful to understand soil differences within the geographic regions when refining forage management recommendations. Crop and soil scientists at the University of Georgia recognize six soil provinces in Georgia: 1) Limestone Valley, 2) Blue Ridge, 3) Southern Piedmont, 4) Sand Hills, 5) Southern Coastal Plain and 6) Atlantic Coast Flatwoods (Figure 3). These soil provinces differ from each other in many ways (e.g., texture, drainage, parent material, organic matter content, etc.). As a result, the forage system must accommodate these differences.

Limestone Valley

This province contains fertile upland soils and zones along streams that make excellent pastures. Good pastures can be produced on almost any land in the valleys. Steep and undulating terrain is mostly woodlands, but some areas can support pasture growth if care is taken to establish sod-forming permanent pastures. Soil erosion potential is high in the Limestone Valley and Blue Ridge soil provinces. When establishing or renovating pastures, establishment practices that minimize the risk of soil erosion (i.e., no-till or minimum till) should be employed. Cool-season perennials make excellent pasture in this province, but cold-hardy bermudagrasses are well-suited to hay lands and pastures in well-drained, sunny sites.

Though this area averages more than 52 inches of rainfall per year, dry weather frequently occurs in the spring, summer, and fall. Some use of drought-tolerant plants is recommended. (For more information about soils in the Limestone Valley, see the Crop and Soil Sciences Department Factsheet titled “Summary of Soil Test Results from Pastures and Hayfields Originating from the Limestone Valley Soil Province in Georgia between 1996 and 2007” at http://www.caes.uga.edu/commodities/fieldcrops/forages/soils/BR.html.)

Blue Ridge

The rich cove lands of this province are well-adapted to cool-season perennial pasture and hay production. Cold-hardy bermudagrasses can be used successfully for hay lands and summer grazing in this area, but are rare because of terrain and drainage issues. Winter annual pastures can be planted on any of the cultivated soils of this province. However, the upland soils have better drainage and are better suited to winter annual pasture. This area receives abundant rainfall (more than 65 inches per year in most areas). (For more information about soils in the Blue Ridge soil province, see the Crop and Soil Sciences Department Factsheet titled “Summary of Soil Test Results from Pastures and Hayfields Originating from the Blue Ridge Soil Province in Georgia between 1996 and 2007” at http://www.caes.uga.edu/commodities/fieldcrops/forages/soils/BR.html.)

Southern Piedmont

The Piedmont region of Georgia contains one large soil province, the Southern Piedmont. This is not to say, however, that areas within the Southern Piedmont are the same. Quite the contrary is true. In fact, the Southern Piedmont is difficult to characterize, as its soils are quite variable.

The Southern Piedmont contains more of the state’s forage-based livestock enterprises than any other soil province. Pastures in this region contain mixtures of cool-season and warm-season perennials, while hay lands are predominantly bermudagrass. Though there are exceptions, the lower Piedmont is generally considered the southern edge of adaptation for tall fescue and the northern edge of adaptation for bahiagrass. As a result, pastures in the lower Piedmont often contain significant amounts of bahiagrass, bermudagrass and tall fescue.

The best land for pastures is along the streams and river bottoms of this area. These low, moist zones are excellent for summer pastures, if adequately drained. Many parts of the Piedmont were extensively row cropped in the 19th and early 20th centuries. Severe soil erosion during this era resulted in the loss of much of the topsoil throughout this area. Though the upland soils still provide good spring and fall grazing, periodic droughts during the spring, summer and/or fall severely limit forage production in this area. Drought-tolerant plants should be used on the uplands for summer grazing. (For more information about soils in the Southern Piedmont, see the Crop and Soil Sciences Department Factsheet titled “Summary of Soil Test Results from Pastures and Hayfields Originating from the Southern Piedmont Soil Province in Georgia between 1996 and 2007” at http://www.caes.uga.edu/commodities/fieldcrops/forages/soils/SP.html.)

Sand Hills

Soil in the Sand Hills province is quite variable, and, as the name suggests, is characterized by sandy soils and undulating terrain. The Sand Hills province is located around the Fall Line (where the Piedmont transitions to the Coastal Plain).

Land that produces row crops in this area will provide acceptable forage yields. Some of the better areas will produce winter and summer annual pastures. However, because many of these soils are quite prone to drought, hybrid bermudagrasses that develop deep-root systems should be used for hay and grazing in this area. (For more information about soils in the Sand Hills, see the Crop and Soil Sciences Department Factsheet titled “Summary of Soil Test Results from Pastures and Hayfields Originating from the Sand Hills Soil Province in Georgia between 1996 and 2007” at http://www.caes.uga.edu/commodities/fieldcrops/forages/soils/SH.html.)

Southern Coastal Plain

Just south of the Sand Hills, the terrain in the upper sections of the Southern Coastal Plain becomes less rolling. Soils in this soil province are typically heavier and more fertile than the soils in the Sand Hills and Atlantic Coast Flatwoods. The best soils are in moist zones along streams. However, productive pastures can occur on better upland sites. Winter annual pastures often do best on upland soils in this area.

The Southern Coastal Plain is the second-largest soil province in Georgia and is home to the state’s official soil, the Tifton soil series. The Tifton soil series is the predominant soil series in the Southern Coastal Plain, occupying more than 75 percent of the lower and eastern part of this soil province. (For more information about soils in the Southern Coastal Plain, see the Crop and Soil Sciences Department Factsheet titled “Summary of Soil Test Results from Pastures and Hayfields Originating from the Southern Coastal Plain Soil Province in Georgia between 1996 and 2007” at http://www.caes.uga.edu/commodities/fieldcrops/forages/soils/SCP.html.)

Atlantic Coast Flatwoods

Flatwoods soils in Georgia are often poorly drained, with the water table periodically (usually in the winter) reaching within a few inches of the soil surface. Soils in this area also commonly contain organic hardpans. As a result, the best pasture soils are on good uplands and well-drained lowlands. Most of the uplands can produce winter annual pasture and perennial summer pasture. Closer to the Atlantic Coast, the soils are predominately poorly-drained and may not be suitable for pasture use. In the Flatwoods soils, bahiagrass swards generally will persist better than bermudagrass, unless the site is well-drained. (For more information about soils in the Atlantic Coast Flatwoods, see the Crop and Soil Sciences Department Factsheet titled “Summary of Soil Test Results from Pastures and Hayfields Originating from the Atlantic Coast Flatwoods Soil Province in Georgia between 1996 and 2007” at http://www.caes.uga.edu/commodities/fieldcrops/forages/soils/ACF.html.)

Soil Types in Georgia

There are literally hundreds of soil types in Georgia. It is not uncommon for a single pasture or hay field to contain several different soil types. Each soil type has its own characteristics. The easiest way to determine what soil types are on a given farm is to examine the soil survey (Figure 4).

Soil Survey Map Figure 4. Example of a soil survey map available from the USDA NRCS's Web Soil Survey (http://websoilsurvey.nrcs.usda.gov/app/).

Most areas of Georgia have been surveyed by soil scientists from the USDA Natural Resources Conservation Service (NRCS). These soil surveys are published by the USDA NRCS either as surveys of single counties or combinations of two or three counties. Though not all counties have a modern soil survey available, NRCS soil scientists are working hard to provide statewide coverage. The status of soil survey work in Georgia can be found at http://www.ga.nrcs.usda.gov/technical/soils/publications.html.

Soil survey information is a powerful tool. In addition to outlining generalized physical and chemical properties of the soil types of interest, it can give relative estimates of crop performance. The soil survey even provides estimates of hay yields on a soil type and the number of animal units a particular soil type can carry.

Hard copies of the soil survey (assuming the survey for the area is complete) can be obtained from the local NRCS office, Conservation District, or library. Fortunately, the soil surveys of most counties in Georgia have been digitized and are available online via the USDA NRCS’s Web Soil Survey (http://websoilsurvey.nrcs.usda.gov/app/). Tutorials and guides on how to use the Web Soil Survey are also available on their website.

Site-Specific Conditions

On every farm, there will be variation that cannot merely be explained by differences in soil type. These differences will often be substantial between fields, and conditions are often highly variable within a field. The variability may be the result of natural differences in soil formation, water-holding capacity, soil organic matter, slope or other factors. However, the most common contributor to differences between fields or areas within a field is historical management (e.g., pastures vs. hayfields, historical applications of nutrients, areas in a pasture where animals congregate versus areas where animals spend little time, etc.).

Soil conditions may be variable enough within a field that it warrants the identification of specific areas that are managed separately from other areas. Such “site-specific management” has been enabled by “precision ag” tools such as GPS, GIS, variable-rate applicators, etc3. These techniques are often more expensive than traditional, uniform management systems. As a result, site-specific management is usually not cost-effective, except for the most intensively-managed forage systems.

Most soil conditions are difficult or cost-prohibitive to change (e.g., soil water-holding capacity, organic matter, slope, etc.). However, the fertility of the soil is easier to improve. The first step in improving soil fertility is to take a soil test (see “Sampling the Soil in Pasture and Hayfields” below). Soil samples submitted through your county extension agent will be analyzed at the University of Georgia Agricultural and Environmental Services Laboratories’ Soil Lab. Lime and fertilizer recommendations will be made based on those soil test results.

Sampling the Soil in Pasture and Hayfields

Urine and Dung Patches in a Pasture Figure 5. Urine and dung patches should be avoided when sampling soils. The prevalence of these hummocks is a common indicator of nutrient deficiencies in other areas of the pasture.

A soil test is the best tool for assessing soil fertility. Soil testing is a chemical analysis that reveals any soil fertility issues that may be limiting production4. The soil sample analysis provides a guideline for the amount of lime or fertilizer needed to correct deficiencies or imbalances in soil pH or available nutrients. These amounts are determined by the specific needs of the crop being grown. Furthermore, soil test recommendations from the Cooperative Extension office are based on decades of scientific studies. Thus, by regularly testing soil and following the recommendations, soil fertility can be maintained at levels that result in optimum productivity of the pasture or hayfield.

The key to soil testing is to ensure that the sample is representative of the area of interest. At the very least, each field should be sampled separately. Soil pH and some nutrients will often vary with soil type. Fields with substantially different soil types should be sampled separately within major soil types.

When sampling pastures, be sure to avoid areas around water sources, shade, mineral feeders, where hay has been fed, or any other area where animals may have congregated and created a nutrient buildup. It is also important to avoid sampling in areas immediately surrounding urine or dung patches (Figure 5). In general, soil samples should be obtained from pastures every three years and from hayfields each year. More information on how to take a representative soil sample can be found in the Cooperative Extension Leaflet 99 titled “Soil Testing”.

The Importance and Role of Specific Nutrients and Soil Amendments

As with all crops, forages must be provided an ample supply of available nutrients. Maintaining optimum soil fertility is critically important for ensuring good establishment, persistence, winter hardiness, pest resistance, drought tolerance, sufficient forage quality, adequate yields, and economic returns. If any nutrient is deficient, problems in one or all of these areas can occur. Thus, it is critical that a good soil fertility program be the basis of any forage management system. This section presents factors that affect the availability of the nutrients in soil, briefly conveys the importance of several essential elements and identifies the most common sources of individual nutrients.

Soil pH

Soil pH measures soil acidity. Most forage crops grow best when the soil pH is 6.0 – 6.5. However, some legume species require a slightly higher soil pH (e.g., alfalfa requires a pH of 6.5 – 7.0). When soils are too acid (pH is too low), crop growth will be reduced. On the other hand, soils can become too basic (pH is too high) when too much lime is applied. Though this can also have a detrimental effect on plant growth, high soil pH values (> 7.0) are rare in Georgia.

When soil pH is kept at the level appropriate for the forage crop(s) being grown, the nutrients stored in the soil will be most freely available to the plant. This increases the plant's ability to efficiently use fertilizer and nutrients already in the soil. Proper soil pH also prevents high concentrations of toxic elements (e.g., aluminum) that can injure root tips and prevent proper rooting. Maintaining the appropriate soil pH also promotes desirable bacterial activity in the soil.

Most Georgia soils are acidic or will naturally become more acidic over time. The addition of ammoniacal forms of nitrogen fertilizer (e.g., ammonium sulfate, urea, UAN solutions, ammonium nitrate, etc.) can accelerate soil acidification. To correct low soil pH, the soil acidity must be neutralized. Lime supplies carbonate ions that neutralize soil acidity (increase soil pH). Agricultural lime is the most common product used to raise soil pH values, though other products (e.g., wood ash, marl, basic slag, egg shells, etc.) can also be used.

Liming agents differ in the amount of calcium and magnesium they contain. Both calcitic and dolomitic limestone contain calcium. However, dolomitic limestone also contains magnesium and should be used (if possible) to maintain sufficient soil magnesium levels. If magnesium is present in adequate levels, then calcitic limestone can be used.

One reason for maintaining a rather neutral soil pH is that it prevents aluminum (Al) from becoming soluble in the soil. When the pH drops, Al becomes dissolved in the soil moisture. Soluble Al is toxic to plants and drastically inhibits root growth. The addition of lime raises the soil pH, and the Al returns to a solid form.

Unfortunately, it is difficult for lime to quickly infiltrate deep into the soil profile. As a result, the soil surface may be neutral while the subsoil is very acidic. In this situation, the addition of gypsum (CaSO4) may be helpful for some crops. Although gypsum does not alter the soil pH, it can infiltrate the soil profile and reduce the toxicity of soluble Al. For example, research with alfalfa has shown significant yield increases in response to gypsum application on some soils with acidic subsoils. A subsoil sample (soil from deeper than 15 inches) must be tested to determine whether gypsum is needed.

Soil Organic Matter

Soil organic matter (OM) plays a critically important role in the biological, chemical, and physical characteristics of the soil. Soil OM supports soil microbes that are critical to making some essential nutrients available to the plant. Soil OM is also important in supporting populations of nitrogen-fixing bacteria that infect nodules on legume roots. The acidifying effects of ammonium fertilizers can be slowed by sufficient levels of soil OM. Soil OM also increases the ability of a soil to be well-drained while at the same time hold sufficient water to promote plant growth. In many of Georgia’s heavy clay soils, high levels of soil OM helps to prevent soil compaction.

Decaying roots, crop residue and animal dung provide the primary source of OM in the soils of pasture and haylands. To retain this OM, tillage operations should be kept to a minimum. Excessive tillage during seedbed preparations, use of aeration equipment, treading damage and other soil disturbances may decrease soil OM levels.

Essential Nutrients

Sixteen chemical elements are essential for normal plant growth and reproduction (Table 1)5. Some of these are non-mineral nutrients (e.g., hydrogen, carbon, oxygen, etc.) that are freely available to all plants, with very rare exceptions. However, several mineral nutrients may need to be supplemented.

Table 1. The 16 nutrients that are essential for normal plant growth and reproduction.
Groups Essential Nutrients
Non-Mineral 1. Carbon (C)
2. Hydrogen (H)
3. Oxygen (O)
Macronutrients
Primary 4. Nitrogen (N)
5. Phosphorus(P)
6. Potassium (K)
Secondary 7. Calcium (Ca)
8. Magnesium (Mg)
9. Sulfur (S)
Micronutrients 10. Boron (B)
11. Chlorine (Cl)
12. Copper (Cu)
13. Iron (Fe)
14. Manganese (Mn)
15.Molybdenum (Mo)
16. Zinc (Zn)

Essential nutrients are generally grouped into two categories, macronutrients and micronutrients, based on the concentration of the nutrients found in the plant. The nutrients required in the largest quantities are called macronutrients and are further grouped into primary and secondary nutrients. Primary nutrients are mineral elements that are needed in the highest concentration and that most frequently need to be supplemented. Primary nutrients include nitrogen (N), phosphorus (P) and potassium (K). Secondary nutrients (calcium (Ca), magnesium (Mg), and sulfur (S)) are also needed in high concentrations, but are not as frequently deficient in most soils. Other nutrients are also essential, but are required in much smaller quantities. These micronutrients include boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), and zinc (Zn).

Georgia soils often do not contain sufficient concentrations of primary macronutrients. Occasionally, secondary macronutrients and micronutrients are not available in the appropriate concentrations for proper plant growth and the addition of fertilizer (inorganic or organic) may be necessary to correct the imbalance. Sometimes, however, this lack of nutrient availability (e.g., micronutrient deficiencies) may be because the soil pH has become too low or too high. Even when a deficiency does exist, there are many cases where the addition of the fertilizer may cost more than the value of the increased plant performance and/or come with some environmental consequence. Thus, the use of soil test-based recommendations from the University of Georgia is critical to the appropriate use of fertilizer.

Nitrogen (N)

Nitrogen is necessary for rapid growth and high yields, and is an essential component of plant proteins. The amount of N fertilizer needed and the correct timing of applications varies with crops and how they are used (for grazing or hay). Application rates for N fertilizer will typically be higher for hay crops than in pastures that are grazed, because N is recycled via the urine and feces of grazing animals. Since the amount of N available from the soil is typically much less than the forage could utilize, N can be effectively used as a tool to increase or decrease forage productivity in pastures, as needed.

Nitrogen-deficient plants will be light green or slightly yellow, especially in the lower (older) leaves, and will be much less vigorous. In pastures, N deficiency is often exhibited by a great difference in growth and color between spots where animals have urinated and the surrounding areas.

Phosphorus (P)

Phosphorus is an essential plant element that plays a key role in many vital plant processes such as root development, reproduction, and energy transfer. Low soil levels of P can cause difficulties in establishing new pastures. This element does not readily leach from most soils, and one application per year is sufficient.

Phosphorus levels in most of Georgia’s soils are naturally low. For forage crops, however, P deficiencies are less frequent than deficiencies in other nutrients. Applications of animal manures have occurred routinely on many areas where forage is produced. As a result, these soils are usually high in P. However, P deficiencies are quite problematic when they occur. Stands that are deficient in P will be stunted, but may be relatively dark green. In grasses, the base of the tiller is often dark purple. In legumes, the leaves will be much smaller than normal and older leaves may be dark green or purple.

Potassium (K)

Potassium is second only to nitrogen in the concentration found in plants, and is essential for producing economical yields (especially when stress conditions occur). It is also critical to maintaining thick, persistent stands (see insert, “Potassium Fertility for Bermudagrass”). It affects plant vigor, disease resistance, forage quality, and winter survival. It is important to split K applications across two or more application times to prevent excess K uptake (described in detail in the “Timing and Method of Nutrient Applications” section of this publication). This is particularly important with alfalfa and bermudagrass stands that are harvested for hay.

Potassium Fertility for Bermudagrass

Each ton of bermudagrass hay will often contain the equivalent of more than 40 lbs. of K fertilizer (K2O). High-producing bermudagrass hayfields may yield well over 10 tons per acre. As a result of this high rate of nutrient removal, K deficiencies occur frequently in bermudagrass hayfields. Stands that are K deficient become less vigorous, less dense, more disease prone, and more apt to winterkill.

In most cases, K deficiency comes about slowly. Deficiency symptoms occur initially in the margins of lower leaves in the form of chlorosis (yellowing) followed by necrosis (death). In fact, a bermudagrass stand may be very old before it begins to exhibit severe stand thinning as a result of K deficiency. However, some varieties are more prone to K deficiency problems than others. For example, “Alicia” is very susceptible to leafspot diseases when K deficiency occurs.

Research has shown that stands can recover if given adequate K supplementation. One major reason for this is that K fertility is critical for healthy rhizomes, the underground stems that aid the spread of bermudagrass. Rhizome production is nearly 800 percent greater when K fertilization is adequate than when K is deficient.

Sulfur (S)

Sulfur is critical to protein formation, N-fixation in legumes, and maintaining root growth. Sulfur may become a limiting nutrient in plants that accumulate high levels of nitrogen in their tissues. In Georgia, the need for S varies considerably. Like N, the S in the soil is held and released

Status and Revision History
Published on Nov 17, 2008
Reviewed on Nov 8, 2011
Reviewed on Nov 30, 2014