Jordan recommends that growers inoculate their peanut seed or fields to ensure that adequate levels of rhizobia are present in each field.
Choose Assurance Over Unpredictability
“The data demonstrate that while peanut response to rotation is often predictable, response to inoculant and rotation combinations is less predictable. Therefore, peanuts should be inoculated in all years regardless of previous rotation history to minimize risk and maintain yield,” he says.
The economic value of inoculation is also demonstrated in these trials.
“Assuming a commercial inoculant cost of $8 per acre, economic return in new peanut fields at $535 per ton was 51 times higher than the cost of the inoculant. A five-fold increase in economic return over inoculant cost was noted in fields with a recent history of peanut production.”
Generally, Jordan says, a peanut plant with 15 nodules on the tap root by 40 days after emergence is showing adequate nodulation.
Based on his research, Scott Tubbs, University of Georgia research agronomist, offers this rule of thumb: It takes around 50 pounds per acre of peanuts to pay for an inoculant application. Yield increases of more than 150 pounds per acre to more than 1,000 pounds per acre have been observed over non-inoculated peanuts in a variety of rotations, including short rotations, and in both irrigated and rain-fed conditions.
Tubbs says, “You may not see benefits from inoculants each and every year, but considering it only takes a 250 pound per acre yield bump once every three to five years to break even on an annual product application, such a decision should be an easy one for most growers to make since the chances of a profitable outcome in the long-term is much greater than not.”
At times, even with the use of an inoculant product, such as when the product was not properly cared for at planting and many of the bacteria died or when soils become saturated after planting and the bacteria are adversely affected, an application of ammonium nitrate may be needed. However, as Tubbs notes, yield will probably not equal a properly inoculated crop.
“On new land, inoculant failure can reduce profit by 200 pounds per acre even when 120 pounds of topdress nitrogen is applied. Foliar nitrogen applications are not cost effective and often cause unacceptable leaf burn.”
This example further shows that properly applying a liquid inoculant is the best way to achieve maximum yield in the peanut crop. “It has been stated before by my predecessors and colleagues, and by me in previous years as well — an inoculant application is one of the most cost-effective ‘insurance policies’ at a grower’s disposal,” Tubbs says.
In 2016, the cool, wet start to the growing season in Virginia and the Carolinas was not good for effective nodulation and early peanut root growth.
“Under these conditions, peanut developed only a few roots with a reduced number of nodules,” says Maria Balota, assistant professor with Virginia Tech’s Tidewater Agricultural Research and Education Center. “Plants were smaller and less green than ‘normal’ plants, in particular when planted in crop residue because this maintained soil cooler and wetter.”
What can be done to prevent poor nodulation?
“One very important thing is to inoculate at planting,” Balota says. “It is also important to scout for the number and size of the nodules in the first 45 days after planting.”
For producers in the Virginia-Carolina region, Balota says, based on her research, the threshold of nodules a farmer should look for at two weeks after planting is an average of five big nodules on the main root; at 30 days, 70 nodules of any size on the main and lateral roots; and at 45 days at planting a producer should be able to find an average of 130 nodules.
If poor nodulation is found at beginning flowering, which usually leads to smaller and yellowing plants, Balota says an inorganic nitrogen needs to be applied.