I have not tried a cover crop after planting fruit trees, but I have used cover crops to prepare my red clay soil for fruit trees. I haven't done a side by side comparison of trees grown with and without such preparation, but I can tell you that the effect on the soil is dramatic.

Last August I killed a 8'X24' section of grass with Roundup, then a few days later planted the "soil builder mix" (45% Bell Beans, 15% BioMaster Peas, 10% Dunsdale Peas; 10% Purple Vetch, 5% Lana Vetch; 5% Common Vetch; 10% Cayuse Oats), which I covered with half an inch or an inch of compost. By October, it was 3 feet tall.

Normally, if I stand on a garden fork in my lawn, it penetrates an inch or two. That's standing on it with two feet (I'm ~210#) In October, after a couple months of cover crop growth, I could easily plunge it in all the way. I've had the same experience with a cowpea/rye mix. An advantage of mixes is that different plants have different rooting patterns, the combination of which will break up the soil more thoroughly. For example, combining something with a deep tap root with a plant that has a broader spreading more fibrous root system will more thoroughly invade the soil with roots.

I can't comment specifically on fava beans, but in general, cover crops are the real deal when it comes to loosening red clay soil. I also don't know if they are as effective on that gray caliche soil I've heard others talk about.

Alex

THanks for the post. I think I'm going to try it. I don't know what caliche soil is, but around here they call it adobe clay. It seems to handle being amended. It's not entirely hard pan any more after years of covering it with mulch. I just wanted to ratchet up my organic skills, so to speak.

I like the list you gave me. I was originally thinking of the fava because they don't have to be turned into the soil necessarily to have benefit. With those other cover crops, I wonder if they have to be turned into the soil? Part of the issue is that I don't want to do too much tilling.

Thanks,
KM

And favas are delicious eating so you'd get a harvest as well as a cover crop.

Over here, many orchards both chemical and organic have permanent cover of NZ white clover.
As a bonus, it attracts the bees.
I'm a massive fan of broad beans (favas) so I'd grow some too. And Bocking 14 comfrey. And multiplying onions. And spring bulbs.
The only things I wouldn't plant are grass and things that need digging to harvest.

Thanks, Alex. That's exactly why I don't wan to till the adobe clay.

I've heard that turning in the favas is a way of composting in place, but I think I can just chop them up and put 'em in the compost pile, too. The idea is to get the roots in there.

Thanks everyone,
Kmama