The heat was so intense that you could almost see it. And if you could see it, it would be the same color as fire. It was probably very humid, so the air felt heavy. In Michigan, where I live, on very hot, humid days, you can feel the air almost as a weight on you. Underneath this horrible heat and this heavy air, there was the dirt (soil). It was hard, dry and unyielding (it would not let you put a hoe into it or a plow through it).
Stooped means bent over, as when a person is unable to stand up straight. I think the rice has had so little rain, that it is bent over, like an old person.
This novel seems to be written in very beautiful language.
The heat was the color of fire. The sky was as heavy as mud. Under this heat and that sky, there was soil. The soil was dry and hard, and it wouldn’t give way to a hoe or plow.