2. Development of BMP Cost-Effectiveness Values
Effectiveness of Land Application Relative to Typical Preexisting
In the Tar-Pamlico basin, the most common baseline condition for cost-sharing of
land application is the application of wastes at greater than agronomic rates
(Section 2.3.1). The net effectiveness of cost-sharing for land application,
therefore, is the reduction in surface and subsurface nutrient loading which
results from reducing land application to agronomic rates. Table 2-3 summarizes
the literature results for studies that have addressed nutrient runoff and sub-
surface drainage from lands receiving wastes at various rates.
Of the studies summarized. in Table 2-3, the most relevant for our purposes is
which was conducted very near to the Tar-Pamlico basin.
Evans et al.
The Evans et al. study is also the only geographically relevant study that has
attempted to quantify both surface and subsurface losses from land-applied
animal wastes. (Although other studies have examined these losses, they were
not considered appropriate for this analysis due to substantial differences in
either soil type, climate, or topography). Evans et al. reported that approximately
13 percent of land-applied nitrogen was lost via surface and sub-surface drainage
when wastes were applied at agronomic rates. However, a mass balance was
unable to account for 28% of applied nitrogen. The authors suggest that part of
this deficit may have been due to N displacement "in the [soil]
sampling zone by subsurface flow." Consequently, the actual subsurface loss
may have been somewhat larger. Based on this uncertainty, we feel that a
reasonable estimate of surface + subsurface N losses for wastes applied at
agronomic rates would be 20% of applied N (80% effectiveness).