Before planting new blocks in our orchard, we roll out round bales of hay repeatedly over several months (or years, as planning allows) to allow it to break down and build up the soil. In theory, it's also a great way to suppress weeds, but until we can bale our own hay, we have to rely on purchased rolls, which often contain seeds, but we're often OK with the tradeoff, since whatever weeds are brought in with the bales tend to be a whole lot easier to deal with than what we're trying to suppress. Over time, rolling out the hay also does amazing things for the tilth of the soil, as well, which is great if you'd like to intercrop at all because you don't need (or want) to till.
We are doing a lot of intercropping of annual produce crops between our apple trees. I actually grew about 5 acres of pumpkins and gourds in this manner this past season and last year with amazing results. The idea with the gourds and pumpkins is also that the vining plants will help further suppress weeds . . . you've just got to stay on top of the vines, because they can't wait to to get their tendrils on the trees. But I wish I could post a photo here of some of this year's plantings. I religiously moved vines into the tree rows and slapped down any climbers, and the result was a perfect mat of vines between trees, just what I'm going for, and last month harvested record (for us anyway) amounts of gourds and pumpkins. I've just planted out some fall produce crops including kale, collards, cabbages, and swiss chard, in a block of hay-mulched apple trees, and they are looking fantastic. I will be planting out garlic in the same manner as soon as I can get to it. Planting (making a hole in the hay mulch, digging a small transplant hole) is a lot of work compared to just thrusting your paws into some newly tilled earth, but the time investment early on has paid off for me in time savings in other ways. For one thing, I do all the bed preparation gradually, just rolling out hay, as opposed to rushing around the weather to mow/disc/till field beds. If I amend the soil in any way, it is only to sidedress with minimal amounts of 5-4-3 Harmony fertilizer.
Disclaimer: it sure would be nice if the apple trees got some benefit from the comingling of these cash crops' roots with their own, but my sole goal here is to further diversify the orchard economically by making efficient use of space, taking advantage of particularly rich and healthy soil, not having to worry about irrigation, and cutting down on my labor of preparing field beds . . . all without taking nutrients away from the trees or otherwise adversely affecting them. And I am limited in my planting options by the size of our growing M111 trees . . . although in blocks where we have more spacing between trees or have more upright-growing varieties, it does work out even with fully grown trees. But in general, during the summer I can only grow crops like pumpkins in younger blocks of trees; larger trees would shade them out. After the leaves have fallen, or before they've emerged in the spring, it's a bit more doable under larger canopies.
My long-term dream is to continue with hay mulch in older plantings (perhaps applied via a square bale chopper that blows it into the rows, since we can't roll out bales efficiently once trees are planted) and inoculate it with mushroom species. Right now, we can only maintain hay mulch around older trees in a very limited fashion, since I have to spread it out by hand, rather than just roll it out in a row before trees are planted. We have encouraging amounts of mushrooms that sprout in the decaying hay mulch. But it's a whole 'nother ballgame to think about cold-turkey, no more copper or other fungicide sprays that might affect any introduced mushroom species. So we'll think about that tomorrow.
And no, voles have not been an issue with the hay mulch or crops, in fact, they and other rodents are much more of an issue where we let the mowing go and maintain waist-high weeds/grass/natives/etc. Our climate is very different from New England, and the hay compacts and breaks down rather quickly. We've also got plenty of black snakes, but I know you folks up North are nervous about mulching for very good reason. I have seen what voles can do, so I'm very thankful it's not the same kind of issue for us, whatever the reason.
Brittany Kordick
Kordick Family FarmWestfield, NC
Zone 7a