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madmagic

Rhizobacteria success with red clover green manure

madmagic
14 years ago

Late last August I sowed my first green manure patch with Red Clover seeds. Not having a handy supply of rhizobial inoculant, I just watered and hoped. By mid-October of last year, the bed looked like this -- you can click the photo for a larger image:

It stayed green and healthy-looking well into the snowy season and rebounded this spring with impressive growth. Currently the clover is 4-6" tall and lookin' good.

However, I was concerned last fall because the roots of the clover did not seem to develop the distinctive nodules of rhizobacteria. Multiple times between sowing and freezeup, I gently uprooted a few plants and checked closely. Every time, the roots appeared entirely free of the characteristic lumps.

Over the winter I read a couple of tips which gave me hope. One tip suggested using a garden tool to break the roots free when checking for nodules. Apparently they are easy to strip off when just pulling the plants out of tight clay soil, which I have.

Another tip suggested many legumes will not show overt signs of colonization by rhizobacteria if there is enough free nitrogen in the soil to encourage good growth. Seems some legumes have the ability to choose their preferred source of nitrogen -- and if it's easier to get their N from the soil than grow it symbiotically, they'll resist colonization.

My guess is -- and this is only a guess -- with the cold soil temperatures of early spring, the available fixed nitrogen in the soil was greatly reduced from last fall. If so, perhaps this stimulated the clover roots to encourage the bacterial colonization.

Once our local night temperatures begin to regularly stay above the 55F mark -- usually by mid-June here, though if the current warm weather continues it could be mid-May -- I'm planning to smother this bed with cardboard, UCG and compost, then plant cucumbers and melons. The nitrogen boost from the decaying clover should be a real help to summer and early fall growth.

All the best,

-Patrick

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