Grass vs. Legume Competition – Does the Winner Tell Us Anything?

If you’re the one who’s been reading this blog regularly :), you know that since May 2011, we’ve been planting summer and winter cover crops to improve our dusty, depleted soil.  We’ve never planted just one species – it’s always been a mix of at least two different plants – at least one grass and one legume.  (For newbies, legumes work with soil bacteria to make their own nitrogen.  Examples:  beans, peas, vetch, clover, alfalfa, etc.)

As the soil health gets better & better over time, I think I’m seeing some of the fields expressing their healthy transition through the types of plants (grass vs. legumes) that are growing.  Could I be seeing things and reading way too much into them?  Quite possibly!  But it’s interesting to think about… at least for me!

Take this picture of our neighbor’s east field from May 2012.  It shows what we lovingly remember as our 3-foot tall “vetch jungle mat”.  But wait… something is missing.  Where’s all the rye we planted with the vetch?  Virtually no rye germinated.  What you see in this pic is 100% vetch.  We were happy to get vetch’s wonderful weed-blocking services and all that free nitrogen.  But we wondered… what in the world happened to the rye?  Why didn’t it germinate and grow?

May 2012.  Neighbor's east field.  Vetch jungle mat.  No rye germinated.

May 2012. Neighbor’s east field. Vetch jungle mat. No rye germinated.

Now check out this pic of the same field one year later, in May 2013.  We planted a winter cocktail of radishes, oats, cereal rye (we’re optimists), austrian winter peas, crimson clover, and lupines.  Both grasses – oats and cereal rye – germinated and grew stupendously.  The oats died in January from hard freezes, but you can see lots of healthy rye (looks like tall, skinny wheat) growing in this picture, along with crimson clover and peas (legumes).  We never put nitrogen fertilizer on this field, so why the extreme change in grass growth in just one year (non-existent to beautiful)?

May 2013.  Neighbor's east field.  Cereal rye growing well with legumes (crimson clover and peas).  Yellow flower is year-old mustard, planted in May 2012.

May 2013. Neighbor’s east field. Cereal rye growing well with legumes (crimson clover and peas). Yellow flower is year-old mustard, planted in May 2012.

Curious, I googled “grass legume competition” and found lots of information and research results, but no solid conclusions.   Many research studies tested grass/clover pastures at different nitrogen fertilization rates and found that more grass grew with higher nitrogen.  Makes sense, because grass loves nitrogen and clover can make its own.  Some researchers documented that added nitrogen made pasture grasses grow so big so quickly that the clover got shaded out.  But, other studies found that different mowing heights and times resulted in the same grass vs. clover effects.  So the precise effect of nitrogen on grass vs. legume competition isn’t clear, but it’s generally accepted that grass loves nitrogen.

We subscribe to Acres USA for the eco-farming ideas.  Many wise old timer farmers contribute to that magazine, and I’ve read from them that legumes are “rescue plants”.  Meaning, it’s hard to get grass to grow well on poor soil, but legumes will germinate and grow well enough on bad soil and will eventually contribute some nitrogen to the soil, enabling grasses to grow better.

So IF legumes are rescue plants AND grasses grow really well with good nitrogen but legumes could take it or leave it, the two pictures of our neighbor’s east field might tell a story.  Maybe the 2012 vetch grew like crazy and the rye didn’t because nitrogen was lacking.  Then, maybe the vetch provided enough nitrogen to get soil functioning so the 2013 grasses (oats and rye) could grow.  I could be dead wrong in drawing these conclusions, but maybe not.  What do you think?  Anyone else out there have thoughts or experience with grasses competing with legumes?

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5 responses to this post.

  1. Posted by Rich on December 18, 2013 at 11:23 pm

    I’ve tried to get clovers (alfalfa, crimson clover, etc.) growing in a pasture of mine for a number of years and have never had much luck. I’ve tried broadcasting seed, drilling with a no-till drill, and even tried feeding it to the cattle with their minerals.

    I’m starting to think that the pH of my soils is too acid for optimum clover growth (if I’m remembering it right, clovers like a pH closer to 6.5-7.0). But, grasses can thrive in a pH of 5.5-6.0.

    If your soil pH was higher than mine, you might have had the opposite problem, and had soil that favored the vetch so much that it out-grew the rye in the first year.

    Reply

    • Hi Rich, good point and thanks for the reminder. I agree soil pH is definitely another significant variable. I had the same problem getting legumes to germinate in pasture. We also tried broadcasting & drilling :) They absolutely refused to germinate until we spread high calcium lime.

      But for this field featured in the blog post, the pH was 6.4 on both fall 2010 and fall 2012 soil tests (no 2011 test). So the pH was a little acidic and was likely the same 6.4 for both the vetch jungle (no rye) and winter cocktail (lots of rye).

      Reply

      • Posted by Rich on December 20, 2013 at 2:50 pm

        “…They absolutely refused to germinate until we spread high calcium lime…”

        That comment made me remember that the last time I tried to get clover established in my pasture and it didn’t really work, that the next time I stubbornly tried to plant clover, I was going to get some pelletized lime and mix it in the drill with the clover seed.

        The idea was that I could create a small zone of “starter calcium” in the furrow that would give the clover enough of a boost to get growing without spending even more money to spread lime over the entire pasture.

        I don’t know if it would actually work, but thanks for the kinda-sorta reminder.

      • you’re welcome :)

  2. Posted by Rob on April 11, 2014 at 1:42 pm

    I noticed something similar in my front lawn where I’ve been growing a rye+hairy vetch cover crop in three sections separated by sidewalks. There’s a front section near the street that got a head start on the others, with earlier application of lime as well as about three inches of compost before a quick buckwheat crop during the summer. The other sections were bare over the summer, and got somewhat less compost before I planted the rye+vetch in September.

    Though there was plenty of vetch growing before winter set in, I can’t find any at all in the front section — it’s just full of rye that’s growing fast. In the other sections, and especially where the rye is sparse and paler, more yellow green, the vetch is starting to take off. As is, unfortunately, some henbit.

    There are a number of other variables involved (such as road salt in the front section and a slightly earlier planting date), so it’s hard to say, but your conclusions about nitrogen seem to fit what I’m seeing.

    Thanks for your blog — I’ve referred to it a lot in deciding the cover crop approach for my yard.

    Reply

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