Soil microorganism populations can explode and tie up the available nitrogen in the soil. Poorly integrated fresh manure can create pockets of poor water and air infiltration. Fresh manure can be applied in the fall and do have certain advantages. The buffer effects are greater, fewer nutrients are lost due to leaching and decomposition, and more bacteria are added to the soil. Crop rotation is the practice in which a crop or family of crops is rotated out of the bed it was in and placed elsewhere the next year.
Crops vary in their specific nutrient needs.
For example, heavy feeders should be rotated into a bed that contained a nitrogen-fixing crop such as peas. The year after, crops that require lower nutrient levels can be planted in that spot. The third year, the legume crop is rotated back in. The fourth year, heavy feeders are finally used again. Rotation is one way to vary the demands on the soil and protect crops from a build up of insects and pathogenic organisms.