Cover Crop Garden: Winter Legume Mix

Winter Legume Mix:

  • Lentils
  • Austrian Winter Pea
  • Crimson Clover
  • Arrowleaf Clover
  • Red Clover
  • Hard Red Winter Wheat
  • Winter Oats
  • Einkorn Wheat
  • Rye
  • Barley
  • Common Vetch
Winter legume-small grain mixture at the OSU cover crop garden.

Mixing in winter legumes to a winter small grains mixture is prevalent in other parts of the county and world.  The benefits of the small grains mixes are still present in these systems.  However, as the small grain total percentage and planted volume are typically lower than when planted without legumes, benefits like canopy coverage and total C may be slightly lower.  While some of the limitations from a small grain only mixture, high C causing immobilization of N in the successive cropping system, are often not as critical if even present following these mixes due to the N contributed from the legume.  

One of the primary challenges with this mixture is getting early cover.  Most legumes have a prolonged early growing period.  These mixed components can be very valuable from numerous avenues later in the season but are known for slower early growth.  Therefore, enough small grains should be in the mixture to provide adequate early season cover, especially if it is intended for grazing.  Another challenge is cost.  Legumes will often be one of the direct costs of a cover crop mixture.  To negate these costs, many growers will plant lower rates of legumes.  However, growers need to ensure enough percentage of volume of the mixture is present as legumes to capture the benefits of that component of the mix.  The final part is to ensure the mix ratio allows for the growth of both crops.  Optimum early-season conditions can result in the small grain growing rapidly and inhibiting significant growth of the legume crop, especially if planted with a high enough rate.  However, lower small grain percentage and higher legumes can increase cost and result in thinner or spotty stands earlier in the growing period.  Spotty stands can be a greater challenge in winter cover crops systems compared to summer system as there is often a prolonged period of limited to no growth during the winter months.  

The most significant benefit of adding legumes into a mixture is potentially supplying the successive cash crop with some N without adding it as fertilizer.  The amount or N rate that growers can expect for their successive crop varies.  With good breakdown conditions early in the season, it would not be unexpected to see 20-50 lbs N/ac being supplied to the subsequent crop.  However, numerous factors will influence this.  Factors like the amount of legume biomass produced, stage of the crop, termination timing and method, and C:N ratio of the cover as a whole will greatly impact the amount that should be expected.  Most legumes reach peak N fixation around flowering.  Shortly after this (depending on the legume) the plant will dedicate more of the sugars produced in photosynthesis toward growing the developing seed than fixing N.  This increases the amount of C in the plant and widen the C:N ratio.  Therefore, the highest N contributions will be when a crop is terminated after flowering but before pod set.  

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