Thank you Leila, your post is inspiring!
Yes, this land is really wonderful and beautiful, and actually does not only host many plant species but also quite a bit of wildlife - many region-specific birds, but also the maned wolf, some moneys and even some jaguars...
No, I actually don't think myself this land is infertile, as we all know
permaculture can solve these sorts of equations. I guess I just did not really know where to start... But I did some research and little by little I am finding what the solutions are. I believe a huge helper will be to connect with the Brazilian biodynamic community as their knowledge seems very strong - I realized most lands in Brazil are actually acidic so I now don't feel like "the only one" anymore.
The area, a hundred years ago (well, that's my guess of when the land was cleared to become a pasture - could be more), was covered with the magnificent "Mata Atlantica" (search Google if you'd like to know more about it).
The grassland is 100% native though - we cannot call any of the plants you see on the pictures "weeds".
Another aspect is that during the last 10 years the area was left entirely wild (no more cows) and we can see some native, pioneer trees (like the "Candeia") reappear.
The rainfall is quite high, yes, but there is a 3 to 4 months dry period over the winter (we are in the middle of it now - the grassland is greener during the summer).
The drainage is very high (70% sand!) and so the soil does not retain much nutrients. My research about the soil analysis results till now tells that the soil is also very much Aluminium-toxic - meaning that not only the nutrients are leached away by the rain but also that they are very seldom available to the plants.
Organic matter is the "MO" column but I could not interpret it yet (as I have no reference) - my guess is that it is low as well.
Yes, it is quite windy here, but most winds are light ones (less than 20 km/h) - it will be great to put up a windmill up there.
And YES, YES and YES about organic matter: I will focus on this fore sure as this land is very thursty for it!
Thank you again!