Brazil has quite the issue with fertile soil.
The country deals with very high rainfall, and the undersoil water moves with a pretty fast gradient, cause of the natural flow of the bigger rivers towards the ocean.
Partially because of, and partially cause of type, the tree's in the area have roots that dont go deep into the floor at all. the roots start from above, and spread out horizontally, not vertically.
That creates quite a big issue. In a regular ecosystem with plenty of rain, tree's and several other eukaryotes have the ability to capture and hold nutrients flowing around. Often because they live in symbiosis with other species like various kind of fungus and baceria who interact with the roots.
Thanks to this, in europe for example the fertile soil is pretty thick. Dont recall out of my head but its at least a meter if not several.
In brazil however, because of the different fauna, the fertile soil is hardly 20-30cm thick. That is nothing. Cut down tree's, and you take away the few barriers you have left. The consequences is that the fertile soil and nutrients, just erode away with the steams (above and under soil) to the ocean.
Because of this, its pretty hard to grow anything there. Its possible that the stadium is in a section where there is no fertile layer left.
I'd like to point out an ecological mistake brazillians make. They cut down large sections of the rainforest for agriculture. However, because of phenomenons described above, they'll have 2-3 harvests at most, and its over.
What they are basically creating, is some kind of desert without fertile layer.