A nutrient management plan is a plan that informs you of the needed nitrates that would improve your land and how to restore them.
Why do I want a NMP
With better improvement of the soil the yield of grass, hay, or other vegitation will improve and provide the needed nutrients to animals. Without knowing what is needed in the soil, you may apply to little of one nitrate and not enough of another nitrate. This would not be as benifical to the land or animals.