During the next two years, another 15-20 percent of the remaining organic nitrogen is slowly released. Unlike nitrogen, almost all of the phosphorus and potassium is available. Excess phosphorus can increase the risk of polluting surface waters, especially where runoff or surface water isn't controlled. When soil tests high in phosphorus, only apply manure in amounts needed to meet the amount of phosphorus the crop will remove. Nutrients aren't the only value of manure.
Manure increases the soil's organic matter and improves physical structure.
This may reduce soil crusting and susceptibility to wind and water erosion. That's because more stable soil aggregates form in the surface soil. When you use manure, you have to be careful to avoid over-fertilization. Phosphorus is usually of greatest concern because it can pollute surface water. Other elements like copper or zinc may also be present in some manures.