Agriculture Reference
In-Depth Information
of activities—some subsidized and some undertaken by farm-
ers at their own expense—nitrogen and phosphorus runoff
from fields in the United States has fallen around 21 percent
and 52 percent, respectively.
In some areas livestock manure is the biggest problem, but
this can be solved with better manure management regula-
tions. When a farmer is deciding how much manure to apply
on each acre, she was previously required to match the nitro-
gen content of the manure with the nitrogen needs of the crop.
However, because regulations allowed her to ignore phospho-
rus, the result was phosphorus runoff. Newer regulations now
require the farmer to match the nitrogen
and
phosphorus con-
tent of the manure to the needs of the plants. Further, farmers
can inject manure into the soil instead of spraying it, which
should reduce total nutrient runoff. Some new manure man-
agement regulations could backfire, so they must be written
with care. For instance, the new phosphorus regulations might
reduce phosphorus runoff, but at the expense of greater nitro-
gen runoff.
Could we reduce fertilizer runoff by switching to organic
production? Experiments from Michigan fields suggest yes.
They find that nitrogen runoff is lower in organic systems com-
pared to systems using chemical fertilizer, even when reduced
levels of chemical fertilizers are applied. One would suspect
that the organic yields were lower, but even if that were the
case, the nitrogen runoff was still lower on the organic fields
for each unit harvested. This does not mean organic systems
always lead to less pollution, for in these experiments nitro-
gen was supplied to organic fields not by the applications of
livestock manure but through nitrogen-fixing legumes. The
use of no-till systems in the experiments were found to reduce
nitrogen runoff, but other studies have found that no-till can
actually increase phosphorus runoff (partly because the phos-
phorus is spread on the field surface instead of being tilled
into the soil). The lesson is that farmers can take actions to
reduce water pollution, but there is no silver bullet that works
