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Dry Bean Inoculation

Though dry bean has a relatively poor ability to fix nitrogen compared to some other pulses, some input suppliers offer inoculants for dry beans in a variety of formulations.

Keep these tips in mind for proper inoculation for your dry beans.

  • Inoculant for dry beans should be used when planting in a virgin field.
  • Dry bean is normally grown on irrigated fields where residual N levels are quite high; if residual N level in the top foot of soil exceeds 40–50 lb./ac., nitrogen fixation will be inhibited and ineffective (often no pink/red nodules will be observed on the bean root under these conditions).
  • Dry bean seed is often treated with Captan®; this fungicide can harm dry bean rhizobium. Only apply inoculant to the seed immediately before seeding, or apply in granular form in the seed row.

Inoculants come in three formulations.

  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.
  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.

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 dry bean inoculant, talk to your input supplier and read all labels carefully.