You can see a lot by just looking sometimes. I recently took a two week vacation. Before I left, I had removed the weeds from three rows of sweet corn in my garden, but didn't get to the fourth row. On my return, I saw that the corn plants that had weeds growing right next to them were several inches taller than all the others.
I gave every plant identical amounts of organic fertilizer and mycorrhizal inoculant, so the difference in height was puzzling. You would think that the weeds would be competitors for nutrients and water. Shouldn't the corn with neighbor weeds be smaller and less vigorous?
Then I remembered a very interesting book that I read some years ago called, "Let Nature Do The Growing - The Fertilizer-free Vegetable Garden" by a Japanese gardener named Gajin Tokuno. I dug out a copy and reread the section about weeds. Here's a quote from the book (available through Amazon):
"In short, instead of regarding them with hostility, it is wiser to realize that weeds loosen the soil and provide important nutrition and to allow them to grow together with vegetables in a natural ecological system."
Mr. Tokuno's advice came from closely observing his garden for many years. He generally advised cutting off taller spring weeds to soil level, but then allowing lower summer weeds to grow alongside the crop plants. This made good sense from my bio-organic perspective, as mycorrhizal fungi link together all adjoining plants in an underground "foodweb" - more plant roots mean more support for that entire web network.
It seems obvious that my taller corn benefited from the presence of the weeds growing next to them, and the weeds may have contributed to the corn's vigor by bringing deeper-buried nutrients up through longer tap roots or even sharing photosynthates derived from solar energy. The mycorrhizal fungi are known to transfer elements from plant to plant within their web network, so in effect the weeds probably "fed" their neighbor corn.
What implications does this have for gardeners and farmers? Well, it does tie in with some USDA experiments where tomatoes were transplanted into chopped-off stands of hairy vetch, which resulted in very impressive yield gains. The researchers were at a loss to explain their findings, but it wasn't a mystery to me nor would it seem odd to Mr. Tokuno.
Cover-cropping, inter-planting and the use of "companion plants," whether they be weeds or legumes or whatever, is a growing strategy that deserves more attention. I would not go so far as to say that any and all weeds are welcome - I'm certain that some are helpful and others are harmful or overly invasive. Next season, I plan to seed some early crimson clover in every-other corn row a few weeks before seeding the corn, just to see what happens. This variety of annual clover is easy to control if you don't let it go to seed.
For large farms, especially those growing vegetables, employing "helper" plants may allow for considerable reduction in the need for fertilizers. The idea would certainly be easy enough to small-scale test on various crops. Once the best types of companion plants are identified the cost benefits could be substantial, not to mention the improved health of the soil as more and more roots decay and build up organic matter to support subsequent crops. If our valuable crop soils could be gradually improved from year to year instead of being gradually depleted, our descendants would be grateful.
I'd be curious to hear from anyone who tried or observed anything similar to my experience with the corn plants.
Side note: Some spammers have been using the BioOrganics email address as a fake to send their garbage. I know because I recently had over 10,000 "returned - undeliverable" messages flow into my inbox. I was not in a good mood that day!
Cheers, and good growing,