I live in southern Spain with a dry (450mm yearly rain) and a rather poor clay rich, stone rich alkaline soil (limestone everywhere). The land is made of terraces separated by drystone walls and is a former lemon tree plantation which has been in disuse for about 10 years. Lots of dead trees and scattered live but unhealthy lemon, orange and mandarine trees. A lot of different weeds are growing on it, some unindentified clumping tall grasses, everlasting, euphorbia, wild carrot, a lot of wild fennel, wild clematis, oxalys in winter, etc...).
My plan is to turn part of the land into a food forest, plant some timber in distant parts and regenerate some parts to grow annual vegetables. In order to prepare the land for the next growing season, I was thinking of growing green manure crops to try and fertilise the land where I'd put the veggie garden.
Despite attending a PDC last year and a very large amount of literature in my possession, I must say I am a bit lost as to where to start. Can anyone offer advice on what cover green manure crop I could use and how to go about it? Should I till the soil to get rid of all the existing weeds and heavily sow something like buckwheat in early autumn when everything starts greening again? Or a mix with mustards and other things? I should have access to irrigation water by then but I don't want to overdo the water consumption either.
And once the cover crop has grown, what do you do? Chop and drop then somehow dig it in the ground? With what tool?
My suggestion is to start with mowing down the weeds before the rain starts so that it is in close contact with the soil as a mulch to protect the soil when it rains and provide cover to any seeds you chouse to add to the mix that is already there and addapted.to that soil. I don't think it is wise to disturb the soil life there until you know how it is and can respond to change.
I get a lot of rain in the winter but it is dry from june to september. My area of poor soil responds best to vetch though it is hard to mow with the scythe I can cut some swaths when it is set with seed and drag them to areas that need the seed. I mulch everything down with a riding lawn mower in september when dry in preparation for winter growth. During spring and summer I mow selectively anything I don't want to reseed like daisies. Some of my wetter areas I can mow with the scythe one or two times to use as mulch for my berry vines and trees. As I mow small areas at a time with the scyte I have got to know my land and what grows best in each area and drawn out a map with a mowing plan for next year according to what is growing in each area. For example remove any tall grass over the strawberries before June. Over the last 100 years many things that were tried as crops have become naturalised and can just be tended with planning.
Hans is spot on, chop and drop for mulching. If you can, see about saving at least two of the surviving lemon trees, they will be a nice part of your food forest.
get some deep rooting forage vegetables like daikon radish and rape going after you have done the chop and drop to get some soil loosening started.
Once those have matured just chop the tops and let those deep roots decompose where they grew, this improves soil humus content and helps water infiltrate deeper.
Lucerne (alfalfa) is also a good plant to use for deep, mineral mining roots and it works great as a chop and drop.
The more things you can grow to cut and let lay as mulch, the better that soil will get and the more moisture it will be able to hold.