Just 3% of the world's land is suited for growing crops. The rest is too dry, wet, steep, or cold, or has erratic rainfall, or poor or erosion-prone soil. Land unsuitable for growing crops often deteriorates very quickly once the the soil surface is exposed.

Only sand remains beneath this center-pivot irrigator near Lambert's Bay in western South Africa. South Africa loses an average of 20 tons of soil for every ton of agricultural crop (wheat, sugar, etc.) produced.