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Pea Inoculation

One of the most important inputs for any pulse crop is inoculant, and several input suppliers offer field pea inoculants in a variety of formulations. Proper inoculation for field peas will reduce – or remove – your need to apply nitrogen fertilizer and will help get your crop get off to a good start.

Inoculating pea with the correct strain of rhizobia will help meet the nitrogen requirements of the pea crop. Properly inoculated pea should not require any extra nitrogen fertilizer.

Nodules will begin to appear on pea roots three to five weeks after seeding. When nodules are visibly red or pink when cut in half, the rhizobia are fixing nitrogen. If no nodules have appeared after this time, inoculation was unsuccessful and a broadcast application of nitrogen fertilizer may be considered.

Nodules on field pea roots will begin to die and turn greenish-brown to brown as the plants reach the late flowering to early pod filling stage.

Formulations

Field pea inoculants come in three formulations. Much research has been done on different formulations of inoculants for use with pea.

  1. Peat Powder Inoculant: Applied directly to the seed with a non-toxic sticking agent, this formulation is a finely ground peat that contains over a billion rhizobia per gram. Peat powder inoculant is one of the most common types used in Canada.
  2. Liquid Inoculant: This formulation, which also contains over a billion rhizobia per gram, is applied directly to the seed, and because it comes in liquid form, a sticking agent is typically included in the fluid. Liquid inoculant comes in bags that make it easy to distribute evenly onto the seed while it is being augered into a truck box or through a drill fill. Liquid inoculant produced significant differences at some sites – when averaged over a number of sites, however, liquid inoculant showed a limited response.
  3. Granular Soil Inoculant: Unlike peat powder or liquid inoculants, granular soil inoculant is not applied directly to the seed but, rather, with the seed in the seed row. This formulation does, however, contain the same amount of rhizobia as both the powder and liquid inoculants and is gaining in popularity because of its convenience. Under cold or very dry spring seedbed conditions, granular soil inoculation has shown considerable potential for producing large, stable yields of field pea and minimizing the risk of growing the crop. The use of granular inoculant resulted in the highest pea yields in cases where a statistically significant response to inoculation was evident.

Generally, it’s advisable to inoculate your seed the day you’re seeding, but different brands or types have different storage limits and recommended application timing. Some types of inoculants can also be mixed with fertilizer or pesticides. When choosing the right field pea inoculant, talk to your input supplier and read all labels carefully.

Some sites show little to no response to inoculation with any formulation as these sites had previous pea crops or naturally occurring (native) rhizobia. When seeding on land with no known history of field pea, it’s best to use inoculant at recommended rates – although some rhizobia occur naturally in soils, it’s important to ensure sufficient numbers of the correct strain of highly effective rhizobia are present when the seed germinates.