Sources factors, including soil P level and management practices, are important to the potential for P runoff loss from fields. The potential for P runoff increases as soil P level increases.  The potential for runoff P increases with:  1) fertilizer or manure application, with greater risk accompanying higher rates of P application; 2) when the probability of a runoff event is high; and 3) in some instances, with surface application of P.  Maintaining ground cover with vegetation and/or crop residues can result in reduced potential for P loss.