If you have some kind of grain seeds available to plant a cover, or green manure, crop I would do that because either one will help prevent soil erosion as well as supply more organic matter and some nutrients as well. I'm not sure what would be available in Uraguay but Field Rye, any of the Winter Wheats, etc. would work well.

But instead of a cover crop, cant i plant something more productive? Like peas. I cant come up with something else, beacause I find beet seedlings too fragile as to keep alive in that enviroment not so well decomposed yet. Instead peas come up stron and fast. Is it better to plant a cover crop or is it the same if I plant peas?

If you want peas and you think they will grow, why not? I almost always plant sooner in my lasagna beds than I mean to, but it always works out fine for me.

Marcia