Weeds in orchards

Well you have ruled out the three obvious solutions so I guess the only other is glyphosate sprayed when required but it is not liked on this forum so I'd better not recommend it. I wouldn't use a weed killer that poisons the soil as that will not do your trees any good so it would have to be one that works through the foliage only.

There isn't anything wrong with grass by the way as long as you keep it well cut which you can with the right machinery and sympathetic pruning to make life easy.

IF you can find a weedkiller which you can spray round the base of trees without it reaching them either through the roots or absorbing through the stem, it is going to take you just as long to go round your 160 trees carefully applying it as it would to put a mulch on.  You could try slices of well wetted small straw bales (preferably from an unsprayed crop) applied when the trees are first planted.

Grass is all very well but fruit trees actually have quite shallow roots themselves and the shallow roots of closely mown grass will compete for nutrients, so a meadow sward with some deeper rooting and/or nitrogen fixing plants would be best.  These will also attract beneficial insects.  You could then rake the hay after mowing around the trees to create a mulch again.  This will necessitate planting at sufficient distances to be able to mow though.

Well you have ruled out the three obvious solutions so I guess the only other is glyphosate sprayed when required but it is not liked on this forum so I'd better not recommend it.

Although it's probably true to say that most fruit and veg growers prefer to avoid using any chemicals on their plots, there are many who have used glyphosate when circumstances suggested it was the best option.

When it comes to "forum policy" it's the use of home-made pesticides and herbicides that we can't be seen to be endorsing or encouraging because it's technically illegal under EU law.

I had problems with weeds in my orchard so I added a thick mulch of chicken poo all around then topped that off with a thick mulch of wood chips spread out beyond the drip line. Each year I top up the bark mulch and it's been great so far. I can use the riding mower all around the trees without damaging any branches trying to get close, and the trees are loving the extra nutrition and steady moisture.

I am not sure from your description what you want to have between the trees i.e. grass or are you going to mulch the area. Obviously I agree that ideally you want to avoid grass or weeds round the base of trees. One of the traditional ways of keeping grass and weeds down in an orchard is geese. It's what I use in my small orchard and they are great. The only thing to be aware of with them is that you do need to protect the trees when they are young or geese will bark them.