NTT general
calibration and validation process
The
Nutrient Tracking Tool (NTT) uses the Agricultural Policy Extender (APEX) model
to estimate nutrient and sediment losses as well as crop yields. APEX uses a
combination of site specific data (crop management information, weather, soil
and slope) and regionalized environmental parameters to estimate the results
produced in NTT program. Simulations are usually done for >30 years and the
main function of NTT to evaluate and compare different farm-management
practices in order to minimize nutrient and sediment losses while economically
optimize the crop production. However, in order to ensure that parameters used
in APEX for the regional NTT simulation are appropriate the following tasks
within each stage are taken:
Stage 1. To obtain a general parameterization for each state/region, a
series of NTT runs simulating common crop rotations, soils and, weather
patterns for the region is done and the results are compared with expected crop
yield and nutrient and sediment loss values obtained from National Agriculture
Statistics Service, USDA (NASS 2017) .
Stage
2. During this stage, the field-scale
measured data from various sources (e.g., local measured studies and
collaborators) are used to finalize the regional
APEX parameters.
Stage
3. The final parameters obtained from
stage 2 will be used to repeat the process described in stage 1. However, the
various conservation practices, common to the local region, are also simulated
and evaluated for all soils and weather conditions during this stage.
Stage
4. The final results are evaluated and
presented to local stakeholders (if any) and collaborators. The results of the
parameterization (for all stages) would be available on the NTT site.
STATE:
GEORGIA
Below
are the results for Georgia statewide simulations of APEX using the parameters
derived through a regional parameterization method (Stage 1). We display the
average nutrient, sediment and water quantity results over all simulations.
Stage:
1
Type
of parameterization: Regional only (no field-scale data
available at this time)
Number
of counties: ALL (159)
Number
of Soils: 4806
Slope:
0-10%
Simulation
Period: 1981-2015
Number
of Scenarios: 4
Scenarios:
Table 1: Crop management scenarios
|
Rotation |
Tillage Operation |
Nutrient management |
|
Corn |
No till |
Commercial |
|
Soybean |
No till |
Commercial |
|
Peanuts |
No till |
Commercial |
|
Cotton |
No till |
Commercial |
Table 2. Fertilizer Application
|
|
Commercial
Only |
|
|
N
(lb/ac) |
P
(lb/ac) |
|
|
Corn |
180 |
60 |
|
Soybean |
- |
40 |
|
Peanuts |
20 |
40 |
|
Cotton |
60 |
60 |
Summary
of Results:
The results below are
averaged over the 35 years simulation period.
A. Crop Yield:
Table
3. Average crop yield for all crop management scenarios
|
|
Corn (bu/ac) |
Soybean
(bu/ac) |
Peanuts
(lb/ac) |
Cotton
(lb/ac) |
|
NTT |
145 (131-183)* |
34.66 (32.96-36.45) |
2805 (2509-3699) |
892 (342-1437) |
|
NASS |
110 (50.00-180) |
26.54 (14.00-43.00) |
3030 (1750-4580) |
841# (N/A) |
*Range (Min – Max)
# USDA NASS Southern Region (https://www.nass.usda.gov/Statistics_by_State/Georgia/Publications/County_Estimates/2017/GACotton2017.pdf)
B. Water Quantity:
Table 4. Annual average hydrologic components
for each crop rotation
|
Rotation |
Precipitation (in) |
Evapotranspiration (in) |
Surface Flow (in) |
|
Corn |
48.92 (43.84-72.97)* |
19.33 (17.99-21.01) |
22.79 (17.52-37.82) |
|
Soybean |
48.92 (43.84-72.97) |
23.10 (21.04-25.17) |
21.32 (16.28-25.88) |
|
Peanuts |
48.92 (43.84-72.97) |
22.21 (18.65-25.40) |
22.96 (16.21-42.78) |
|
Cotton |
48.92 (43.84-72.97) |
27.60 (22.75-32.13) |
15.45 (10.23-29.55) |
*Range
(Min – Max)
C.
Water
Quality:
Table
5. Annual average nutrient and sediment loads for each crop rotation
|
Rotation |
Organic
N (lb/ac) |
Organic
P (lb/ac) |
Sediment
(tons/ac) |
Surface
N (lb/ac) |
Surface
P (lb/ac) |
|
Corn |
1.32 (0.17-10.39)* |
0.14 (0.01-1.02) |
0.05 (0.00-0.48) |
38.99 (12.16-85.56) |
0.71 (0.37-1.27) |
|
Soybean |
3.02 (0.46-12.12) |
0.47 (0.06-2.34) |
0.31 (0.03-1.98) |
10.36 (6.13-21.25) |
0.58 (0.41-1.00) |
|
Peanuts |
12.21 (1.03-85.98) |
3.53 (0.53-17.88) |
1.82 (0.31-11.94) |
20.96 (12.17-48.49) |
1.31 (0.85-2.39) |
|
Cotton |
13.71 (1.52-63.64) |
3.37 (0.60-19.14) |
1.35 (0.21-10.80) |
25.65 (14.99-43.19) |
1.39 (0.96-2.85) |
*Range
(Min – Max)