Peanut Soil Management
Peanuts are a leguminous crop that fix atmospheric nitrogen. Much of the focus on soil fertility for peanuts is calcium. Calcium is needed in the pegging zone (top 3 inches of the soil) where the fruit or nuts absorb calcium directly from the soil rather than through the roots.
Calcium: Soil testing can help determine how much calcium is present and how much more is needed. Gypsum usually supplies the needed calcium as well as sulfur for peanut production. University of Georgia recommends 500 – 1000 lbs of gypsum per acre around early bloom depending on soil test level. Virginia type peanuts and peanuts grown for seed should receive a ton or 2000 lbs per acre. When lime is used to supply calcium to peanuts apply at planting because calcium in lime is less soluble than in gypsum. Only use lime when looking to increase soil pH. Do not deep turn soil after liming applications. Water is needed for peanuts to absorb calcium from the soil. The critical pod fill period when calcium is needed is 60-90 days after planting. For dryland peanuts avoid planting too late so critical pod fill period lines up with high rainfall months June-August. Too much rain around early bloom can also be problematic for gypsum application. During years when wet conditions delay gypsum application during early bloom period, or if gypsum is ever in short supply, calcium chloride or calcium thiosulfate can be applied through the pivot on irrigated land 60-90 days after planting. Deficiency in calcium in the pegging zone leads to ‘pops’ or unfilled pods as well as pod rot and black heart issues.
pH: Ideal pH for peanut is 6.0 – 6.5. Add lime if soil pH tests below 5.8 with a target pH of 6.2-6.5. Generally, dolomite is recommended over calcitic lime because of cost and the presence of magnesium. If soils test high in magnesium, calcitic lime is recommended to avoid interference with calcium uptake. When pH is low peanuts risk aluminum and zinc toxicity. Manganese deficiency often occurs in high pH soils of 6.3 or above.
Nitrogen: Consider applying liquid inoculant or using seed treatment each year to insure biological nitrogen fixation. Apply inoculant if field has been out of production for more than three years. I am not aware of any research that suggests application of nitrogen fertilizer increases peanut yield.
Phosphorus and Potassium: Peanuts have deep tap roots making them good scavengers of phosphorus and potassium. Apply phosphorus and potassium based on soil test recommendations. If you send soil samples to a private laboratory ask for the Mehlich 3 extraction, especially if you are enrolled in the BMP program. Rotating peanuts with field corn often provides enough residual phosphorus and potassium. Excess potassium in the pegging zone can interfere with calcium uptake. A calcium potassium ratio of 3 to 1 is recommended in the pegging zone. Apply all needed potassium or phosphorus at or near planting. There is no advantage to split applications.
Manganese: Deficiencies often occur in high pH soils. Manganese is often applied through foliar sprays but there are products that can be applied to the soil as well.
Boron: Boron is generally applied through foliar feeding 0.25 lb boron per acre during the first two fungicide sprays. Avoid applying more than 0.5 lbs boron per acre a year because excessive foliar boron can be toxic to peanuts.