Land applied manure is an excellent source of phosphorus (P) for meeting crop growth needs but needs to be managed to minimize P delivery to surface waters. See Phosphorus in Aquatic Systems. Phosphorus movement from agricultural land to surface water is determined by the interaction of:
- soil characteristics and management practices with
- mechanisms of P transport, such as runoff and erosion.
Several soil and P management options may be considered to reduce P delivery to surface waters:
- Maintain soil test P levels near the optimum for crop growth. Risk of loss is greatest when soil test P levels are excessively high. Soil test P is often increased with repeated manure application.
- Practice conservation tillage or no-tillage to minimize erosion, and therefore, the potential of P delivery.
- Apply manure when there is a relatively low risk of runoff during the weeks after application. Avoid application on frozen and snow-covered soil as a runoff event may occur with snow-melt.
- Incorporation of manure may reduce potential for P runoff but may increase the potential loss to erosion. For more see Agricultural Phosphorus Management.
Injection of slurry manure can reduce risk of P runoff if ground cover is maintained to prevent erosion.
Phosphorus transport to surface waters is largely determined by erosion and runoff, distance to concentrated water flow or to surface waters, and by management practices that trap sediments and nutrients carried by runoff and erosion before these enter surface waters.
- The potential for erosion and runoff are determined by the amount of precipitation and intensity of rainfall events, slope steepness and length, soil type, crops grown, and crop and conservation management practices. Some of the erosion P is readily available to aquatic vegetation and some eventually becomes available.
- Conservation practices, such as terraces and farm dams, that reduce runoff, erosion and sediment delivery generally reduce P delivery to surface waters.
- Vegetative filter strips on hillsides and well-placed vegetative buffer zones along streams can be effective in filtering out sediments and some nutrients before they enter surface waters.
- Most of the P that enters surface waters may come from only 10-20% of the area of a watershed, and especially from areas that are very near to concentrated water flow. Alternative management practices may be needed for these sensitive areas.
Potential for P loss from a field, or part of a field, to surface waters is often assessed using a P index that considers field and management factors as well as transport factors. See more…
Educational Resources on Manure Phosphorus Management
- Basic Concepts of Soil and Water Phosphorus
- Field and Management Factors
- Transport Factors
- Assessment of the Risk of Agricultural P Delivery
Extension Resources on Manure Phosphorus Management
Scientific Resources on Manure Phosphorus Management
Page Manager: Charles S. Wortmann, University of Nebraska-Lincoln