Would you consider lucerne in the deep limestone land?
I’ve been messing around with companion crops with a while, and I’ve no real success with clovers.
The lucerne, once established, is damn hard to kill. I’ve used up to 9L/ha of glyphosate on it to no avail. It will live happily underneath a cereal crop and not compete with it in any way. Once the crop is removed, the lucerne will grow away the finest. Before the next crop you can graze, bale, cut or mulch the lucerne, and plant another crop into it... even if you have weeds or volunteer cereals, you can spray it off with glyphosate, and do no harm to the lucerne. The most efficient way to remove lucerne is the plough.
The reason is asked about livestock is when establishing the lucerne it would need one full year on its own...the lucerne can be cut, bales and sold. A 22-24% protein forage is valuable...then after that first year, just ignore it. It’s excellent at fixing N and opening up the ground at depth. The roots will go down to 2m.
Seed is very expensive, around €15-20/kg, and planting at 15-18kg/ha, it becomes expensive to establish. However if interested I can organize HSS lucerne for substantially less than that.
Clovers as companion crops are, IMO, expensive and really tricky to get established in a beneficial way. The newer hybrid clovers are good but too expensive to be considered.
Cc crops, IMO, need to give significant and fast return on investment, otherwise why do it? I’m giving up on phacelia, mustard, radish etc, because the benefit doesn’t show as fast as squarrosum. Squarrosum is also by far the cheapest clover you can buy at around €2-2.5/kg. Squarrosum will nodulate N from before the rosette stage, loves water, and will put up with severe winter temps without any bother. It grows to about 4 feet high so you can bale and sell before planting your spring crop...or leave in place, mulch it and dd into the thatch. It’s quite deep rooting also.
There’s a friend of mine farming 850ha of organic tillage with 20yrs and I’ll run it by him on what to use with the shallow soils over granite.
I know that I’m probably going to stand on the toes of some posters here by dissing the usual cover crop mixes/varieties etc, but if you’re not getting an instant and quantifiable return for the investment and time it does become a little questionable.