Environmental Engineering Reference
In-Depth Information
Subsurface losses of total nitrogen were reduced for conservation tillage from 7% to 36% relative to
conventional tillage. Combined losses of nitrate in surface and subsurface runoff range from -208% to 35%
for conservation tillage relative to conventional tillage. Casman (1990) indicated that a well designed and
properly applied conservation tillage system could probably reduce total nitrogen by 35%.
Ellis et al. (1985) found that total phosphorus was reduced by 50% and increased by 9% for surface and
subsurface runoff, respectively, for chisel tillage compared to conventional tillage practices. The removal
efficiency for surface and subsurface runoff combined was 32%. Gaynor and Findlay (1995) found that
average orthophosphate loss was 1.7-2.7 times greater for conservation tillage than from conventional
tillage, and transport of total soluble phosphorus and total phosphorus increased 2.2 and 2.0 times,
respectively. However, Gaynor and Findlay also reported that conservation tillage increased surface runoff
39% and decreased tile drainage 20% compared to conventional tillage. This was attributed to higher soil
moisture content and decreased infiltration during spring storms. These unusual runoff results may have
contributed to the poor phosphorus removal characteristics in this case. Casman (1990) indicated that a
well designed and properly applied conservation tillage system probably could reduce total phosphorus
by 35%. Casman (1990) also concluded that on the basis of the available data, conservation tillage practices
alone do not consistently reduce nitrogen and phosphorus to surface and subsurface waters. However,
Casman reported that conservation tillage in conjunction with nutrient management can be expected to
reduce nutrient loss.
Structural best management practices —Kreis et al. (1972) analyzed the effect of passing runoff
from a beef feedlot through a series of ponds and waterways. The runoff was held in detention ponds for
several days before being discharged into a 2-mile long grassed waterway. The grassed waterway did not
substantially reduce concentrations of total phosphorus, total organic nitrogen, and nitrate in surface flows.
As discussed previously with respect to concentrated flows in vegetative-filter strips, sedimentation and
nutrient transport are not appreciably reduced when vegetation is completely submerged. Thus, the
primary function of grassed waterways is to stabilize ditches and reduce gullying, and they should not be
considered a BMP for nutrient removal.
Langdale et al. (1985) studied the combined effects of a farm-management plan composed of
conventional tillage with terraces, grassed waterways, and nutrient management (i.e. fertilizer level
selected on the basis of soil tests). They found a 66% reduction in total phosphorus load relative to
conventional tillage. Given that grassed waterways contribute little to total phosphorus reduction, it is clear
that terraces can substantially contribute to total phosphorus reduction in runoff from agricultural areas.
Nutrient management —According to the Chesapeake Bay Nutrient Reduction Task Force, a nutrient-
management plan is a management practice that provides recommendations on optimum nutrient-
application rates, times, and methods based on soil- and manure-analysis results and expected crop yields
(Camacho, 1990). These plans, when properly applied, contribute to the reduction of nutrient inputs to the
land while maintaining or improving crop productivity. In practice, nutrient management is a composite
of several practices including various degrees of reduced fertilizer application, split application, subsurface
banding, and spring (and not fall) fertilization (Casman, 1990).
Each of the features of a nutrient-management plan is important in reducing nutrients in runoff and
obtaining good crop yields, but the amount of fertilizer application is a particular concern. Farmers in
many places follow a principle that “if 1 kg is good, 2 kg is better.” For example, Casman (1990) notes
that poultry farmers on the Delaware, Maryland, Virginia Penninsula, U.S., apply 2-4 times the
recommended amount of manure with respect to N, and with respect to P manure is applied at even
higher rates. In order to feed China's massive population fertilizer use in China is much higher than in
the U.S. China's per hectare chemical fertilizer application grew rapidly from less than 10 kg in 1960 to
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