Unlike commercial fertilizers, manure has no guaranteed analysis. The amount of nutrients in manure cannot be changed so that exact nutrient amounts always are applied. Also, applying the plant-limiting nutrient in amounts needed for best crop production may overapply other nutrients. Overapplication of nutrients can adversely impact surface and groundwater. Of special concern is nitrogen, which converts to nitrate, the plant-available form.
Nitrate ions are soluble and are extremely mobile in saturated soils.
Both nitrogen and phosphorus can cause problems if carried into surface water bodies such as streams and lakes. These nutrients stimulate growth of aquatic plants and can limit fish survival. Nitrates also can affect adults, but the evidence is less certain, and concentrations need to be much higher to have an impact. Young livestock also are susceptible to health problems due to high nitrate levels. Fecal bacteria in livestock manure can contaminate drinking or recreational water, causing infectious diseases such as dysentery, typhoid, and hepatitis.