hello everyone!
a friend of mine recently obtained some land in Capinha in
Portugal the soil is not on its best condition its been on hiatus for the pass 4-5 years and before that was used to grow a monoculture (potatoes i think) probably with lots of pesticides and one of the best assets was stolen two big oak trees  . there's not much growing there now apart from some weeds here and there. we go there sporadically but don't spend much time,  we're planning to move there next year, and i would like to ask if there's anything i could do to enrich the soil until then. I thought about planting some herbs in one of this sporadic visits and then later use them as green manure, what kind of herbs should i plant that would be more beneficial to the soil? i heard about comfrey and cloves would be a good nitrogen fixating plants any other suggestions? what's the best course of action to quickly revitalize the soil?  Any suggestions on what we should cultivate on our climate? any tips are welcome thank you !

Do you mean that the ground is bare of all plant life except a few patches of weeds?  You might need to do some earth work to make habitable pockets for plants to establish in the first place if that's the case.

If you can, though planting a cover crop is definitely a good idea.  I've used purple clover before, and have seen wheat and barley used in conjunction with it.  No reason not to obtain a yield you could eat   Comfrey is probably the single most useful plant to have around.  It's pretty impossible to kill, though, so I wouldn't recommend blanketing large patches of ground.  We usually plant it as a border plant and cut it back regularly to super-charge our compost with.

Also, don't look at the weeds and think you need to wage a war.  Dave Jacke basically equates weeds to pioneer species that are there to work the soil when other plants (like herbs, prairie grasses, etc) can't establish themselves.  Dandelions have deep tap roots that bring nutrients up from the lower regions of the soil.

Is it too late in the season to be planting a cover crop on the whole land like that?  Maybe you could cover it next spring?  When next year were you planning to move there?  FYI, I'm in SE Iowa, so our climates are probably nothing alike, but someone else here probably has suggestions for plants and planting times in your area.

yeah most of the ground is quite dried up except for the area near a river which has some bushes i got bit worried for not seeing many weeds and such due to the fact it as been abandoned for quite a while i was expecting nature to take over. i think the next spring for the clover and other herbs is the more viable way, I'm planning to move there hopefully by the end of uni year so around May - June. 

You might try willow and/or wisteria near the river. Willow trees are very easy to propagate from cuttings and grow quickly; a copse of them cut every couple of years will produce a lot of wood, which can be used to retain moisture up-slope.

This concept has been discussed in other posts, but the basic notion is that sticks can be laid out along a slope to catch runoff for a new planting; some weeds and soil can then be piled over the wood during the wet season. You might start this by pruning dead wood from some of the bushes, and maybe collecting any slash that the thieves left when they stole the oaks. The place to start is probably about halfway up the slope, at places where the land is somewhat cup-shaped to begin with.

I've read that pigeon pea is a good long-lived plant for dry, infertile soil, but I don't have much experience with it. It will produce food, good compost, and eventually even some wood.

Where there currently are weeds, I'd suggest slashing them down and sowing some small-seeded fava beans (where I live, bags of them are available cheaply from the Muslim grocer, the Arabic name being "ful mudammas") right as the dry season is ending. Most of the way through the wet season, I'd suggest thinning the favas to the point that they produce well, and spreading the cut plants out to extend the fertile area at the edges, then covering them with more cut, dry weeds and perhaps planting some fenugreek for the summer in that new area.

Bundles of dry fava bean stalks can also be hung out as a nesting site for mason bees. Mason bees don't produce honey, but they also don't sting and are generally less effort and expense than domesticated bees.

I'm not sure clover will be appropriate for much of the area if the soil dries out completely. Locations near the river, or over buried wood, should work OK. There is probably a plant that resembles clover growing on the property already, maybe black medic. Chances are there is more of a niche for annual plants like black medic, which is only alive while water is fairly plentiful, than there is for a moisture-loving perennial like clover.

Many Thanks for the great suggestions Joel!!

if you are leaving the land empty for a year..i would suggest if you have an opportunity to, you might try planting a bunch of seedlings of trees and mulch really well around them (not right up to the trunk as rodents could be a problem then) and of course protect the trunks with some wire or fencing..or wrap..

and haul in as much mulch and organic matter as you can and spread it around the area where you put the trees or might want a garden..that way it will rot..you could also put it over cardboard so that will rot as well.