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?
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)?
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?