Part 1, Section 2: Soil Fertility Management
Soil Fertility Management
MANURE NUTRIENT MANAGEMENT
Approximately three-fourths of the nutrients harvested in crops grown on a farm, and in the purchased feed and supplements fed to the livestock, may be recycled back to crop fields in manure. Thus, manure nutrient management always has been and continues to be an important economic consideration on farms with livestock or poultry.
There is growing concern, however, about the effect of nutrient management on environmental quality. A nutrient management law requiring some farms with high animal concentrations to have a formally approved nutrient management plan has been in place in Pennsylvania for a number of years and was revised in 2006. (See Agronomy Facts #40, Pennsylvania's Nutrient Management Act: Summary of the Regulations, for more details.) This law affects farms that have more than 2 animal equivalent units (AEUs) per acre. (One AEU = 1,000 lb of live weight of any animal.) (See Agronomy Facts #54, Pennsylvania's Nutrient Management Act: Who Will be Affected?, for more details.) Environmental concerns thus add to the importance of proper nutrient management on all farms in Pennsylvania.
Nutrient management is not the same for all farms. It is important to recognize the differences among farms and realize how they affect the choice of appropriate management strategies. As an aid for determining the appropriate nutrient management options, farms can be classified into the following three management categories.
Category 1—Less than 1.25 AEUs per acre routinely manured, or less than 50 percent of the feed coming from off the farm. Available manure on these farms generally is not adequate to meet total crop nitrogen needs. Thus, additional nutrients in the form of purchased fertilizer or other sources are required for achieving optimum crop yields. Usually, because of the nutrient deficit, these farms are not as likely to cause environmental problems unless there is gross mismanagement.
Nutrient management plans for this type of farm emphasize practices designed to make the most of nutrient efficiency and achieve the maximum crop response from manure nutrients. A well-planned nutrient management program emphasizing economic and agronomic efficiency should reduce the need for purchased inputs and thus should improve farm profitability.
Category 2—1.25 to 2.25 AEUs per acre routinely manured, or 50 to 80 percent of the feed coming from off the farm. Available manure on these farms can meet a significant part, if not all, of the nitrogen requirements for crop production. Because these farms often are at the upper limit of being able to safely handle all the nutrients produced, nutrient management changes on these farms may offer potential environmental benefits. Practices to maximize the safe use of manure and to balance nutrient inputs with removals from farm fields are emphasized, rather than nutrient use efficiency.
The economic return from improved nutrient management on this category of farm is likely to be minimal. That is, a large cost probably will not be associated with implementing improved nutrient management practices; but unlike the first category of farm, little profit incentive exists either. The incentive for change on this category of farm is environmental protection.
Category 3—More than 2.25 AEUs per acre routinely manured, or more than 80 percent of the feed coming from off the farm. Manure on these farms generally exceeds nitrogen requirements for crop production. It is unlikely that all of the manure can be used safely on these farms. Only part of the nutrient management program is field based. A significant component involves off-farm cooperation for acceptable offfarm uses for the excess manure. An economic cost is likely to be associated with implementing an environmentally sensitive nutrient management plan for this category of farm. Nutrient management programming most likely will result in environmental benefits, as excesses on the farm are reduced. This is the group of farms primarily targeted in the Pennsylvania nutrient management law.
This simplified classification scheme is intended to demonstrate the implications of differing situations for nutrient management approaches. Individual farms in each category will not necessarily fit all the characteristics described for the category. When a question exists about the classification, it should be resolved based on more comprehensive, specific information. The animal unit criteria in the categories above are for nitrogen-based planning. These criteria should be cut in half for phosphorus-based planning purposes.