Soil tests from soil samples taken immediately after harvest of crops in the fall can be used to determine lime as well as fertility requirements for crops for the coming year. If soil pH needs adjusting, fall is a good time of the year to apply needed lime since it may take as long as six months for full reaction. However, some reaction does occur soon after application. Bacteria, which fix nitrogen in relation to the peanut plant, do better and form more nodules with an adequate calcium (Ca) level and with pH around 6.0 or higher. If the crop that precedes peanuts is well-fertilized, there may be enough residual nutrients in the soil to make direct fertilization unnecessary. The analysis and report of the soil sample will also indicate which nutrients are needed on a particular field. Calcium and magnesium (Mg) may be supplied by limestone. If no lime is needed, Ca can be supplied by gypsum, and Mg can be included in the fertilizer. If phosphorus (P) is low, add P according to soil tests.

The same is true for potassium (K) and other nutrients needed by peanuts. Boron (B) and manganese (Mn) are normally the most deficient micronutrients on sandy soils. Therefore, if peanuts are to be planted on a sandy soil, it would be advisable to use B at the rate of 0.5–0.75 lb of elemental B per acre. Higher rates of B can be toxic to the plants. Applications of B should be split since it is a highly leacheable, mobile nutrient. High application rates of other nutrients can make B deficiency more pronounced.

The deficiency that we most often associate with B deficiency is internal fruit damage called “hollow heart”, which reduces the quality and value of the crop. However, in more severe cases, B deficiency can result in split stems and roots, on the lower part of the stem with shortened internodes, terminal death, and extensive secondary branching. Leaves may be dark green and mottled with few or no peanuts developing on stubbed pegs. Some fields have been observed with these symptoms recently and this is a reminder that there is a reason to apply B even if few visual observations of deficiencies are seen. B may be applied early with herbicides or with fungicides to avoid making additional trips across the field. The crop may take up less than a tenth of a pound per acre but it is still important for crop production.

Peanuts with a yellow cast during the growing season can have several causes including poor nodulation, micronutrient deficiencies, water logged soils, or herbicide damage. Some fields are yellow due to being water logged which results in poor nodulation and nitrogen fixation. Plants usually grow out of this as soils dry out. Iron and other micronutrients may be limiting in water logged soils too, which will grow out of it as soils dry out.

Manganese deficiencies often occur in soils that have been limed for years and have a pH above 6.3. These symptoms can be seen as a light green to yellow cast to the peanut canopy and are usually more prevalent late in the season and on sandier sites. Manganese applications can be made to the crop or a base application may be made at planting. It is possible to lower the pH through acid forming fertilizers such as ammonium sulfate; however, applications of a few pounds of micronutrient may be more cost effective and the response will be quicker than changing the pH.

Lime should be added if the soil pH is below 5.8, with the target pH being 6.2–6.5. If lime is needed, both a dolomitic or calcitic lime can be used and additional Ca as gypsum may be needed on larger seed varieties. In addition to reducing soil acidity, calcitic lime supplies the plant nutrient Ca while dolomitic lime supplies both Ca and Mg. Peanut responds very little to direct fertilization of most nutrients. However, Ca is needed in high levels by peanut for developing a viable seed.

High levels of Ca are not necessary to grow a healthy plant. The amount of Ca taken up by the plant is dependent on the concentration in soil solution and on the amount of water moving into the plant. Calcium deficiency results in high incidence of pod rot and unfilled pods called “pops”. These peanuts also have lower germination if saved for seed.

Georgia research has shown that Ca applied as lime should not be turned under and that turned under lime had yields similar to no lime. Even though peanut has a lower Ca requirement than soybean or cowpea, peanut does have an exceptional need for Ca for seed maturation and quality.

Lime should be applied to fields well in advance of planting and may be applied to strip tilled fields as a surface application. For those growers who use minimum tillage and strip tillage, surface applications are acceptable. We have long term plots that have not been turned or had lime incorporated for 35 years that are still producing good crop yields.

A high Ca and P layer can develop in the top two to three inches after many years of surface applications of fertilizer and lime. Calcium is routinely applied as gypsum at pegging on sandy soils for rapid replenishment of soil solution Ca. This is not as necessary on heavier soils or fields with irrigation that have higher diffusion gradients toward the pods. Since peanuts are often grown on sandy soils, which are drought prone, there is a limited ability of these soils to replenish the soil solution Ca. Heavier soils and irrigated soils are better able to supply needed Ca for proper uptake. The Ca needs are primarily for pod and seed development and not for growing a healthy plant. Test soils and apply needed amounts of Ca for good yields and quality.

The critical period for Ca absorption begins about 20 days after pegs start entering into the soil and may extend for an additional 60 days. However, some researchers have reported that 69% of total Ca uptake occurred between day 20 and 30 after pegging begins. It is then a necessity that proper amounts of Ca are supplied for the first 30 days after pegging begins.

The problem occurs when limited soil moisture coincides with the high Ca need period and there is no moisture for Ca to be in solution for uptake by peanut. Sandy soils in the peanut region have low moisture retention capacity which leads to moisture induced Ca deficiency.

Much of the irrigation installed in the Southeast was due to corn in rotation with peanuts. High levels of K and Mg in the soil can inhibit uptake of Ca and therefore peanuts are often not fertilized and “high cal” lime is used instead of dolomite. Soil test levels of about 450 lb/A of Ca result in maximum yields of runner type peanuts while levels almost double this are necessary for maximum yield of Virginia type peanut as noted from research by S. Hodges at the University of Georgia.

The larger peanuts have a smaller surface-to-weight ratio and require a higher concentration of soil solution Ca in order to provide adequate Ca to the pod. Therefore, if soil samples show only Ca to be low, then calcitic lime would be satisfactory. However, if both Ca and Mg are low, then dolomitic limestone should be selected.

Lime should be applied three to six months before planting peanuts, but can be applied up to time of planting. Lime should be applied in the fall to allow time to react with the soil.

If Mg soil test is not low, use calcitic lime so that Mg will not compete with Ca for uptake by peanuts. Gypsum is often applied to peanuts at pegging time so that peanuts will have an adequate Ca supply.

Rates of 250 lb/A of dry gypsum in a band to 1000 lb/A of wet gypsum are often applied to peanuts that are to be saved for seed or when the soil test shows a need. Recent research from Alabama over several SE locations has shown that non-irrigated peanuts may have proportional yield increases with gypsum applications up to 1500 lbs/A.

Peanuts may not always respond to rhizobium inoculation. The main reason for this is that there is an indigenous population of rhizobium called cowpea miscellany that is common to many native plants. These organisms are potentially able to nodulate a crop of peanuts grown for the first time in a field. Peanuts are only moderately efficient in fixing and translocating atmospheric nitrogen (N). With soybean, as much as 80% of the plant N comes from the atmosphere while about 55% of the plant N needs of peanut are from N fixation.

Calcium is important to nodulation, and maximum peanut root growth occurs at a pH of about 7.3 while shoot growth, nodulation, and N fixation is best at a pH range of 5.9 to 6.3. An application of lime can improve the availability of Ca, Mg, and P and decrease aluminum toxicity.

Inoculants may be applied to soils that have not had peanuts grown on them for several years or at all. In some cases inoculation can increase nodulation and in others little response may be noted. However, inoculants are cheap insurance in providing needed N for plant growth. Nitrogen fertilizer will not normally increase yields unless the N-fixing bacteria that live in nodules on the peanut roots are not present. If needed, a commercial inoculant can be applied in the seed furrow at planting to provide the needed bacteria.