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Duck Creek Watershed, Texas
Problem Statement
 A
growing poultry industry has developed in southeast Texas,
prompting concerns of impairment from land application of
litter. How can the type of water quality impairment seen
in other poultry production regions of the country be avoided
in southeast Texas?
Objectives
Employing the CEEOT-LP modeling framework, simulate
the economic and environmental impacts of broiler industry
growth scenarios for the Duck Creek watershed. Simulate
the economic and environmental impacts of the most viable
broiler practices for phosphorus control.
Research Methodology
Baseline conditions and
environmental and economic impacts of best management
practice (BMP) adoption and industry expansion were simulated
using the CEEOT-LP modeling framework. Specifically, the
following practices and expansion scenarios were defined
and simulated:
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Expansion Scenarios
- Year
2000 conditions (1X)(baseline for expansion scenarios)
-
Double the litter spread at current rates (2X)
-
Full expansion at current litter application rates
(2.3X)
- Full
expansion at N application rates (6.1X) (N rate) (baseline
for BMP scenarios
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BMP
Scenarios
-
P application rate (P rate)
- Double
P application rate (double P rate)
- Complete
haul-off of litter (complete haul-off)
-
Hauloff of cleanout litter
- Phytase
addition to broiler feed (phytase)
- Alum
addition to broiler litter (alum)
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Environmental Analysis
Modelers used the Soil and Water Assessment Tool (SWAT) as
the water quality component of CEEOT to simulate environmental
baseline measures and environmental implications of expansion
and BMP scenarios. SWAT is a continuous-time, long-term simulation
model designed to predict the impact of management on water,
sediment, and agricultural chemical yields in large ungauged
basins. The model operates on a daily time-step and uses specialized
commands to route water, sediment, and agricultural chemicals
through a watershed. Simulations of expansion and BMP scenarios
were performed by modifying crop management data files to
accommodate changes in land area and application rates and
modifying the nutrient coefficients in the fertilizer database
to reflect changes in nutrient content for BMP scenarios.
Land management regimes were specified on a hydrologic response
unit (HRU) basis. HRUs are virtual subbasin units characterized
by distinct soil type and land use. Fertilizer management
regimes for HRUs were specified to simulate either commercial
fertilizer application or litter application, based on the
land area needed to accommodate the litter generated for each
BMP or expansion scenario. Supplemental commercial N and sometimes
K fertilizer were assumed applied on litter fertilized land
to meet recommended levels, when litter nutrients alone did
not reach these levels.
For the phytase scenario, a litter P reduction
of 25 percent was chosen as a conservative average value,
when phytase is supplemented in broiler diets at recommended
levels. The alum addition scenario simulates the addition
of alum to broiler litter at rates designed to significantly
reduce soluble phosphorus in broiler litter. Based on research
findings, addition of alum to broiler litter was simulated
by reducing the modeled total phosphorus content in alum treated
litter to 20 percent of that specified for untreated litter.
Another model adjustment was to increase the simulated N content
of alum treated litter by 2.9 lb/ton to reflect research findings
indicating greater N content in alum treated litter.
Economic
Analyses
Economic Impact Analysis
Economic impact analysis of
broiler industry expansion in Robertson County was conducted
using industry multipliers developed with IMPLAN Professional
2.0 software using a Robertson County 1997 structural matrix
supplied by the Minnesota IMPLAN Group. Type I and type II
multipliers were used to calculate indirect effects, induced
effects, and total impacts from initial direct effects of
industry expansion.
Economic
Impacts of BMP Scenarios
Economic impacts of BMP scenarios
were estimated using partial budgeting analysis. Partial budgeting
analysis quantifies changes in costs or benefits due to BMP
implementation. Changes in quantities of commercial fertilizer,
broiler litter, and amendments (alum and phytase) that were
directly specified or induced by BMP scenarios, were multiplied
by prevailing prices to estimate the economic implications
of BMP scenarios on a per acre or per broiler house basis.
Costs of BMP scenarios were calculated for representative
operations (pasture, hay, and broiler) by multiplying per
acre or per broiler house costs by the applicable number of
acres or broiler houses for the representative operation.
Costs of BMP scenarios at the watershed level were also developed.
Poultry integrator costs and benefits are also included in
watershed estimates. Cost-effectiveness ratios, at the watershed
level, were calculated by dividing the watershed cost for
each BMP by its environmental effectiveness in terms of reducing
simulated ambient P loads in Duck Creek.
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