Cover crops: the C:N ratio

[MickThompson]

Something to think about if you are trying cover crops to build soil nutrients. C:N is the ratio of carbon to nitrogen in the standing crop. The max you really want to shoot for is 20:1. Much beyond that, and the soil microbes have to consume soil N to break down the carbon. I noticed a lag this year after a wheat heavy cover crop and this is what it was. Termination date matters as well. The older a crop is, the higher the C content. I'm thinking I'll skip the wheat and go with higher N cover instead this round.

The trade off is weed suppression. Nothing trumps winter grains in that aspect.


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[WTM]

thats why i stressed seeding ratio of nurse crop/legume. BUT, what of using as a weed suppressant vs tilling it in as i remember turning a high carbon crop under would cause a C:N imbalance but in a no-till situation it is not as dramatic?

you will still have an imbalance by using a higher N cover crop because of breakdown time, 4-8 weeks. if your garden vegetables dont use it all in that period then excess N will be leached.

i had a bumper crop but i planted an oat nurse crop with winter peas in my planned rows. this year i will stagger those rows and rotate my garden vegetables accordingly which i think helps.

my seeding rate this year was 1:2 oats:winter peas and terminated it at flowering and not any later. i also let it sit for 15 days.

 

[MickThompson]

I think what got me last year was the deer got in there and wiped out the turnip bulbs and set back the clover, and then wheat came on with a vengeance. Can't decide if I will add any grains this year or not.


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[WTM]

yeah that would throw the balance off probably.