Ken, I think the wide grid is because traditionally in Spain people would grow wheat, or indeed beans and the wide spaces were simply more accessible to tractors. It is a huge issue though as with 7-8 months of drought these areas basically become like a rock (and then the first heavy rain washes the top 5-10cm away!). So I definitely think to increase planting density first, and underplant now with very resistant herbs. Would love blackberries, though
. Ar eyou able to grow any berries where you are?
As for nitrogen, I am planning to use carob trees, have a lot of young trees arund the property, they are literally miraculous trees, completely drought and pest resistant and beautiful, too. Although there is some discussion about their nitrogen fixing, so maybe need to re-think that!