Ames, Iowa, USA
July 1, 2010

Peanuts need high levels of nitrogen to produce high yields. Like other legumes, some of the plant’s nitrogen needs are met by the oxidation of soil organic matter.

“The majority of the nitrogen requirement, however, is supplied by bacteria residing in nodules on the plant’s roots,” says Justin Clark, Becker Underwood field development specialist for peanuts. “Most researchers agree that peanut plants respond better to the nitrogen produced by nodules on the roots than the application of nitrogen fertilizer. Whether a commercial inoculant was used or not, conducting in-field evaluations of peanut root nodulation can provide growers insight on how to increase yield potential of the crop the next time peanuts are planted in the field.”

Evaluating Nodulation
Peanut nodulation checks require only a few basic tools — a spade, a bucket of water and a sharp box cutter or blade — and the knowledge of what to be looking for. Be sure to conduct enough checks to provide a good representation of what’s taking place in the entire field. Clark offers the following tips for effective evaluation of nodulation on the roots of peanut plants.

Timing:

• Start checking plants five to six weeks following emergence and until pods mature.
• Poorly inoculated fields may exhibit yellowing of plants at approximately 45 days after planting. Although yellowing of plants may be associated with other causes, it is best to check plants for active nodulation.

Process:

• Use a spade to dig up the plant’s root system, making sure to collect as much of the root system as possible.
• Do not pull the plant as this can cause nodules to be separated from the roots.
• Carefully remove soil from around the root system.
• Soak roots in a bucket of water and gently remove the remaining soil.

Evaluation:

• Start with an examination of the overall mass of nodules, not just the quantity of nodules. Tap root nodules are evidence of inoculant application. Nodules on the lateral roots tend to be less active and may not be fixing nitrogen for the plant.
• Count the number of nodules. Few nodules indicate a problem. A large number of nodules, though, doesn’t necessarily mean the plant is actively fixing nitrogen.
• Slice open several nodules from the tap root and laterals to check and compare the color inside:
  • Pink to bright red — Actively fixing nitrogen
  • White — Indicates colonization by rhizobia, but they are not yet mature enough to start fixing nitrogen (check again in a few weeks.)
  • Green, brown, tan, black or mushy — Not active, ineffective or may be parasitic
• Nodules that don’t turn pink or red tend to be from native rhizobia that were in the soil and may not be specific to peanuts.
• Record the number of nodules per plant, their color and location within the field for review in post-harvest evaluation.
• If few nodules are found, or the color of the nodules does not show active nitrogen fixation, make another check in ten days as conditions may have slowed the development of the rhizobia.
• If nodulation rating indicates the need for nitrogen, and plants appear yellow to pale green in color, consider applying nitrogen.

“A lack of nodules,” Clark says, “indicates the need for use of a commercial inoculant before planting peanuts again in that location.”

Poor Nodulation – Potential Causes
Stresses on the plant and the rhizobia during the growing season can adversely affect the nitrogen-fixation process. Clark says using an inoculant at planting can help producers achieve even higher yields when any of the following conditions occur:

• Old inoculant — Always use a fresh inoculant containing high counts of vigorous, efficient and peanut specific rhizobia. Don’t use an inoculant left over from the previous year or rely just on native rhizobia present in the soil.
• Improper storage of inoculant product — Inoculants contain live organisms and need to be stored in conditions as close to those found in the soil. Avoid exposing inoculant materials to direct sunlight and store them between 40° to 77°F.
• Inoculant too far away from the seed — Applicator drop hoses and nozzles need to be properly positioned so the inoculant is placed near the seed.
• Improper calibration — Using too low of rate of inoculant can result in not enough inoculant being available.
• Planting too shallow — If seed and inoculant are not placed deep enough in the soil, the live rhizobia can die due to lack of moisture, too high of temperature, exposure to sunlight or of a combination of these conditions.
• Too much nitrogen — Having a large amount of nitrogen fertilizer in the soil and available to the seed can curtail nodulation.

“Applying a commercial peanut inoculant is an accepted best-management practice now used by most top peanut producers,” Clark says. “The use of VAULT® peanut inoculants ensures that fresh, vigorous rhizobia and other biological components are present in adequate numbers for maximum effectiveness, nitrogen fixation and yield potential.”

ecker Underwood, Inc., founded in 1982, is an international developer of bioagronomic and specialty products. In addition to being the leading manufacturer of seed coatings and colorants, the company is also the leading global producer of inoculants, beneficial nematodes, and a wide range of agricultural and horticultural products. To learn more about its products, visit the company’s Web site at www.beckerunderwood.com

Website: http://www.seedquest.com/yellowpages/americas/usa/b/beckerunderwood/default.htm

Published: July 1, 2010