Phase 5 Agricultural Land Use

November 9, 2004

Sara Brandt

Chesapeake Research Consortium

Chesapeake Bay Program

Three sources of Land Use Data

• RESAC Land Use– 2000 only

• Agricultural Census– Available for 1982, 1987, 1992, 1997, 2002

• Urban Hindcast– Available for 1990 and 2000

Final Land Use Categories

• High Density Pervious Urban• High Density Impervious

Urban• Low Density Pervious Urban• Low Density Impervious

Urban• Alfalfa• Nursery• Pasture• Hay with Nutrients• Hay without Nutrients

• Composite Crop with Manure (high and low till)

• Composite Crop without Manure

• Extractive• Barren• Mixed Forest• Deciduous Forest• Evergreen Forest• Natural Grass• Water

Phase 5 Ag Land Use Categories

• Pasture• Nursery• Alfalfa• Hay w/o Nutrients = Wild Hay + Orchards +

Idle Cropland + Fallow Cropland• Hay with Nutrients = Total Hay – Wild Hay -

Alfalfa + Failed Cropland

Phase 5 Ag Land Use Categories

• Composite Crop without Manure = Cotton + Tobacco + Vegetables + White Potatoes + Sweet Potatoes + Berries

• Composite Crop with Manure = Total Corn + Soybeans + Small Grains + Total Sorghum

+ Dry Edible Beans

Ag Census Data

• Ag Census Data is used to increase the accuracy of RESAC Ag and to determine acreage of Phase 5 Ag categories.

• Ag Census Data available on a county scale for years 1982, 1987, 1992, 1997, and 2002.

Ag Census Data Gaps

• Crop data in a county may be omitted due to a limited number of farms reporting the item or to avoid disclosing information about individual farms.

• To estimate data gaps, the difference between the State Total acres and the sum of the county acres was distributed to the counties with omitted data in proportion to their average crop acreage.

Crops in which data gaps exist in <5% of counties in Ag Census:

• Pasture• Corn • Hay

• Make up 72% of Total Agriculture in Bay watershed and S. Virginia

Crops in which data gaps exist in >50 % of counties in Ag Census:

• Tobacco• Peanuts• Sweet Potatoes• Rye• Popcorn• Sunflower• Triticale• Sorghum• Dry Beans• Cotton

Make up 1% of Total Agriculture in Bay watershed and S. Virginia

Doublecropping

• Many farms in this region practice a two year corn-wheat-soybean crop rotation.

• In calculating the Composite Crop with Manure, a simple summation of corn, wheat, soybeans, and dry beans would double count crops in this crop rotation.

• Composite Crop with Manure was calculated as the difference between the Total Cropland and the sum of all other non-doublecropped cropland.

Crop composition in Phase 5 Landuse

0

2000000

4000000

6000000

8000000

10000000

12000000

14000000

16000000

18000000

20000000

1982 1987 1992 1997

Nursery

Comp w/o Manure

Alfalfa

Hay w/o Nutrients

Hay w/ Nutrients

Composite w/ManurePasture

RESAC and Census Ag Estimates

Difference between Total Ag from Ag Census and RESAC

0

10

20

30

40

50

60

70

DE MD NY PA VA WV

mill

ions

of a

cres

RESAC Ag

Census Ag

• 25% mean difference, varies widely between counties

• Large difference in VA may be driven by lack of data in So VA

14%

Incorporating Ag Census into 2000 RESAC

• Ag Census is interpolated to 1990 and 2000• RESAC Ag category is replaced by Total Ag from

Ag Census• In order to keep the total county area fixed, all

other RESAC land use categories are adjusted proportionally to the probability that they have been spectrally confused with Ag land, as determined by Edge Analysis.

Edge Analysis

• Inaccuracies in RESAC arise from spectral confusion around the edges, where one land use class borders another.

• For each county, a 60 meter buffer determined the acreage of each land use around the edges of Agricultural areas.

• Proportional acreage of each land use surrounding Ag areas represents the probability that Ag will be spectrally confused with that land use.

• Spatially explicit measure of land use class confusion

RESAC Ag Forest Urban Barren/Natural Grass

1000 5000 600 100Ag Census 2000

Must subtract 1000 acres to keep total area fixed

Edge Analysis 65% 30% 5%

Adjusted

RESAC

Ag Forest Urban Barren/Natural Grass

2000 4350 300 50

1990 Land Use

• Do not have a reliable 1990 RESAC product

• 1990 Urban derived from impervious and census data

• 1990 Ag area from interpolation of Ag Census

• Remaining county area distributed to other land cover classes proportional to 2000 RESAC

All other years

• Do not have a RESAC product

• Urban derived from interpolation of 1990 and 2000 urban

• Ag area from Ag Census

• Remaining county area distributed to other land cover classes proportional to 2000 RESAC

Fudging it in Southern VA

• MLRC 2000 and NLCD 1992 used to fill in where RESAC was not available

• Urban Hindcast not available in S. VA, NC, or TN

• Total urban from MRLC/NLCD data parsed into pervious/impervious and high/low intensity development based on watershed average ratio

RESAC coverage area

MLRC 2000

NLCD 1992

Watershed Landuse Composition

0%10%20%30%40%50%60%70%80%90%

100%

1982 1987 1990 1992 1997 2000

Forest Ag Urban Extractive/Barren/Nat. Grass

• 14% decrease in Ag (3.5% watershed area)• 57% increase in Urban (3% watershed area)

Total Ag

15000000

15500000

16000000

16500000

17000000

17500000

18000000

18500000

1982 1987 1992 1997 2002

Change in 2002 Ag Census Methodology

• 2002 Ag Census includes a “coverage adjustment” to account for under-representation of farmland in Census mailing lists

• Undercoverage in the Census Mail List is estimated by independent area frame survey

• Census data items are weighted based on characteristics of farms in area frame survey that are not on the Census mail list

• Full documentation of Census methods available at: www.nass.usda.gov/census/census02/volume1/us/us2appxc.pdf

Change in Ag Census Methodology

• Coverage adjustment in 2002 Census provides a more accurate accounting of agricultural land but cannot be compared with past Censuses

• NASS provides 1997 Census with coverage adjustment for historical comparison

• Overall 5% increase in Total Ag using new Census method

• Differences vary widely between counties and crop type.

Total Ag

0

1000000

2000000

3000000

4000000

5000000

6000000

7000000

DE MD NY NC PA VA WV

"Old" Census Methodology With Coverage Adjustment

1.1%

<1%

5.8%

4.4%

6.8%

5.3%

3.8%

2002 census

• Need to reconcile 2002 Census with previous Censuses.

• Estimates of % of acreage not covered in Census Mail List published with each Census can be used to determine the coverage adjustment for each state.

Fertilizer Application

Fertilizer Sold

Manure Mass-balance

Non-NM acres w/ all leftover fertilizer

Non-NM acres w/ leftover manure

starter fertilizer, with manure applied after

Manure on NM acresAcres of crop w/o manure

Volatilized fertilizer

NH3NM crops

w/o manure

NM acres w/ manure

Non-NM acres

Volatilizedmanure