Seminole Crop E News

Agricultural News for Farmers and Agribusiness in SW Georgia

Peanut Inoculant Considerations

Posted by romeethredge on April 11, 2014

We are fortunate that legumes including peanuts fix nitrogen from the atmosphere in the presence of a good inoculant so we don’t have to supply this nutrient ourselves.

Here are some peanut inoculant considerations for 2014 by Dr. Scott Tubbs, UGA Cropping Systems scientist.

 It’s been a cool and wet winter, and we’re coming out of what was the wettest year on record in many locations.  This would be a good time to refresh your memories on peanut inoculant applications.   Because of the conditions mentioned above, the rate of survivability of native Bradyrhizobia present in the soil is likely to be much lower than in most years (regardless of how many years it has been since the last time peanut or a cross-inoculating species was grown in a field).

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Therefore, I would highly recommend growers to strongly consider the investment in a peanut inoculant at-planting this year, especially in poor draining fields that had standing water for more than a couple days.  When soils are saturated, oxygen is depleted and several things can occur with respect to these bacteria.

First, if heavy rainfall occurred shortly after a liquid inoculant was applied the last time peanuts were grown in a field, it is possible that the concentration of the Bradyrhizobia bacteria was drawn away from seed furrow from dilution or leaching.  Saturated conditions can also kill the bacteria leaving lower native populations for infecting future peanut plantings.  When saturated conditions occur while peanuts are growing in a field, N-fixation is halted since oxygen is needed in this process, but is not readily available in the soil pore space since water occupies all of that volume.   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.  Without taking the time to run the dollar values at current prices, I can still safely say that in most years it takes merely a 50-80 lb/ac increase in yield to cover the cost of the inoculant application at planting.  You will not see benefits from inoculants each and every year, but considering it only takes a 250 lb/ac yield bump once every 3-5 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.

Also keep in mind that the product is listed on the label to be delivered at around 1.0 fl oz per 1,000 linear row feet (may differ slightly depending on which product is selected).  This is developed for single row application.  Inoculant application is not like adjusting seeding rate, where you are pulling half of the amount out and moving it over to the adjacent twin furrow.  With an inoculant, the applied amount needs to be per furrow, therefore a twin row planting inoculant application will double the amount of inoculant applied compared to a single row planting.  I have no data to support using a half-rate of inoculant per furrow to keep the total application rate per acre the same as a single row planting.

   Some additional reminders regarding inoculant formulation decisions:

  • When applied at labeled recommendations, the amount of viable cells delivered on a per acre basis does vary by formulation, with the liquid inoculants supplying the most (8.3 x 1011 cells/ac), followed by sterile peat products (5.8 x 1011 cells/ac), and granular supplying the least (2.4 x 1011 cells/ac).  However, this should not be the primary deciding factor on which formulation to select.

  • Sterile peat/powder formulations are only recommended if there is no way of applying the other formulations.  To get good coverage/sticking of the product to the seed, the seed need to be moistened.  This requires drying time to prevent messy planter problems.  When applied dry, there will be inadequate seed coverage.  I have data showing reduced nodulation and yields using this formulation compared to the other formulations.

  • Do not confuse the granular inoculant formulation with the sterile peat/powder formulation, they are not the same.  The granular formulation, while also a dry product, is not applied to the seed prior to planting, it is metered through a dry metering box such as an insecticide/herbicide hopper and placed in-furrow.

  • Regardless of formulation, these are living organisms.  If you want them to remain alive/viable, then don’t leave them sitting in the cab of a hot pickup truck or tractor, nor exposed to direct sunlight.

  • Likewise, since this is a living medium, exposure to certain pesticides designed to kill living organisms (insecticides, fungicides, etc.) may adversely affect the product.  Minimize exposure to such products, and consult the labels/websites/representatives for more information about mixing of products.  There should be minimal concerns of exposure to typical peanut seed treatments, and short-term exposure to common in-furrow fungicides in the case of tank-mixes.  But a chlorine-free water source must be used as the carrier for liquid inoculants.

  • When soil conditions are relatively dry, liquid inoculants will disperse away from the intended target, thus the concentration of Bradyrhizobia near the seedling upon emergence and early season growth when infection should be occurring may be hindered.  The granular formulation will remain at the bottom of the seed furrow, where intended.  Therefore, in non-irrigated conditions with only marginal soil moisture, granular products should be considered.

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