Converting Your Farm to Organic for Profit and Pleasure—Chapter 3: Soil Building Green Manure Options, the Second Principle of Organic Agriculture

Part 3: To start, please permit me to add a few more words regarding green manure termination. Thanks to research done in the 1990’s in Saskatchewan, we understand that the best time to terminate a green manure legume crop is in the early bloom stage. After that stage of plant development, there is little additional nitrogen produced, as the main focus of the plant now turns to seed production. Hence the majority of the energy in the plant switches from vegetative growth to seed development. The nodules, which produce the nitrogen for the whole plant, begin to shut down, dry up and slough off the roots. Nitrogen from all parts of the plant, roots, stems and leaves, begins to trans-locate into the growing seed for protein production as the seed begins to develop.

The goal of green manure, however, is not seed production but soil nourishment. Since the plant has reached its overall goal of maximizing vegetative growth as well as nitrogen production, it is terminated. This plant material can then be incorporated into the soil to feed and nurture it without using any more valuable moisture. Of course, the crop itself is nurturing the soil while it is growing, its roots supporting a host of microbes. This is an additional advantage that chem fallow does not provide and is well understood by those growing cover crops. I believe there are other important advantages of cover crops that could be incorporated into our current green manure system. We are currently studying cover crop systems in adjoining regions and setting up experiments on our farm which will test the best ways to combine the advantages of both cover crops and green manure systems for our area.

So, to conclude this chapter on soil building, I have included a summary of advantages, as well as disadvantages, we have seen from each green manure crop we use here on our farm:

SPRING PEAS

  • Large seed
  • Seed in spring (as early as possible)
  • 90 lbs/acre
  • Low water usage
  • Minimal organic matter
  • Low nitrogen production
  • Fair annual weed competition (with a good stand)
  • Seed preference: Arvika Spring Peas (produces more biomass in the spring than Austrian Winter Peas)

CLOVER

  • Small seed
  • Companion seed with cash crop (green manure 2nd year)
  • 6 lbs/acre
  • Higher water usage
  • Greater organic matter
  • Higher nitrogen production
  • Better weed competition
  • Seed preference: Yellow Blossom Sweet Clover
  • ATTENTION: Watch to make sure it doesn’t grow into the wheat crop in the first year, if it does, it must be swathed before harvest so as not to stain the grain with clover juice which will give the grain an unpleasant flavor
  • TIP: Clover weevils will destroy seedlings in the year following a clover year on the prairie so avoid seeding clover in those years.

ALFALFA

  • Small seed
  • Companion seed with cash crop the first year (hay the 2nd year and green manure the 3rd year)
  • 6 lbs/acre
  • Highest water usage
  • Most organic matter
  • Highest nitrogen production
  • Best weed competition (a good stand will compete with annual weeks like Canada thistle)
  • Seed preference: an irrigated type of alfalfa (easier to terminate in green manure year than dry land varieties)
  • ATTENTION: Hardest to terminate
  • TIP: Double-work fields during termination year to avoid escapes

BUCKWHEAT

  • Intermediate seed
  • Seed in early June (when soil is warm)
  • 25 lbs/acre
  • Intermediate water usage
  • Lowest organic matter
  • No nitrogen production
  • Good weed smother crop
  • OTHER BENEFITS: solubilized phosphorus and tap root opens soil for better water absorption
  • TIP: terminate before first seeds mature

WINTER PEAS

  • Large seed
  • Seed in late August to early September (before seeding winter wheat)
  • 90 lbs/acre
  • Low water usage*
  • Minimal organic matter*
  • Low nitrogen production*
  • Fair weed competition (with a good stand)
  • Seed preference: Austrian Winter Peas
  • CAUTION: Winter survival has been a hit and miss, but we intend to try adding barley as a companion seed in the fall to increase winter survival.

* a little more than spring peas

NITROGEN TIP: It is always a good idea to do soil tests for nitrogen levels before seeding your cash crop to assess the result of your green manure effects. It may also be helpful to do nitrogen level soil tests prior to seeding your green manure. If you already have a lot of nitrogen, you might choose a green manure crop that uses less water and produces less nitrogen.

green manure crop infographic

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