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Peanut Inoculant Considerations

Inoculant Considerations (R. Scott Tubbs)

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).  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.   I have approval from administration to purchase a new twin-row planter  with the ability to apply liquid inoculant in-furrow, but the planter will not  be in place this season.  We will begin  addressing issues such as these and other long-overdue questions related to  single vs twin rows in multiple crops starting next year.

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.