GMMAT, Your right, cop rotation avoids a decrease in soil fertility, as growing the samecrop repeatedly in the same place obviously would eventually deplete the soilof various nutrients.A crop that leaches the soil of one kind of nutrient is followed during the next growing season by a dissimilar crop that returns that nutrient to the soil or draws a different ratio of nutrients, for example, rices followed by cottons. You are correct, fertalizers are expensive, especially when your dealing with 1k+ acres of crops. But farmers around here are getting that money back, plus income when they sell there corn harvest. And when corn goes up 1.50 a bushel, a little nitrogen isnt a big deal to farmers.