The vast majority of the winter pasture in the Southern Great Plains is wheat. There are many reasons for this, including culture, the opportunity to harvest and sell grain, and government and insurance programs.
Ben Franklin wrote, "When the well's dry, we know the worth of water." Unfortunately, the "well" is running dry in many parts of the world. Rivers are running dry prior to reaching the seas because we are over-allocating and overusing them.
Traditional soil test methods have typically involved treating a soil sample with various acids and other reagents to extract a portion of the inorganic nutrients in the soil. This can hopefully be done with as few processes as possible to be fast and cheap, and fit the industrial model.