Grass controls erosion…but does grazing cause nutrient pollution?

Grass controls erosion…but does grazing cause nutrient pollution?

70 -85% of N and P ingested passes thru the cow.70 -85% of N and P ingested passes thru the cow. 500-1000 kg N/ha/yr directly under urine and fecal patches. 500-1000 kg N/ha/yr directly under urine and fecal patches. Excretions by grazing cows cover only about 15% of Excretions by grazing cows cover only about 15% of

pasture surface in any 1 year.pasture surface in any 1 year.

MIG allows:MIG allows: Seasonal milk Seasonal milk

productionproduction Modest production/cowModest production/cow Much lower cost per Much lower cost per

CWTCWT Higher Higher profitability.profitability.

But less control over But less control over manure & urine manure & urine distribution?distribution?

Bailing samples from Confined A watershed piezometers.Bailing samples from Confined A watershed piezometers.

Farmland covered in Farmland covered in perennial grass instead of perennial grass instead of annual crops.annual crops.

Little erosion or sediment Little erosion or sediment lossloss

Cows managed to ‘harvest’ Cows managed to ‘harvest’ feed and ‘spread’ manure. feed and ‘spread’ manure.

Low need for imported Low need for imported feed, fertilizer, fuel.feed, fertilizer, fuel.

Management Intensive Grazing (MIG)Management Intensive Grazing (MIG)

Grass stands still Cows harvest feed, “haul” manureCows harvest feed, “haul” manure

Objectives were to…Objectives were to… Objectives were to…Objectives were to…

• monitor nutrient concentrations in groundwater under 4 MIG and 2 confined-feeding watersheds.

• estimate nutrient loading from 1 confined feeding and 2 MIG dairy farms.

• calculate whole farm nutrient balances for the 3 farms. • determine if organic forms constitute significant part of N and P

leaching losses.• Use results to inform regulators about suitability of MIG as

environmental Best Management Practice.

The Three Project Farms at a Glance The Three Project Farms at a Glance

12.36.71.3P

1476446NSurplus lb/acre

21 T/acre/y351 (810)167 (348)AUD2 orManure

6 yr: corn/oats/alfalfa

pasture/ 24% legume

pasture/ 8% legume

Vegetation in study watersheds

110.5AU1/acre

605175204Farm, acres

ConfinedGrazer2Grazer1 

1 AU = one animal unit of 1000lbs 2 AUD = annual AU days per acre, days of grazing by milk cow herd. Does not include heifers or calves. Assumes cows graze 365 days year-1.

Profit: $/CWT: 6.99 4.34 3.60

Research Approach:Research Approach:

• Studied 2 grazing and 1 confined feeding dairy farm, each with 2 watersheds (A and B).

• A transect of 3 piezometer nests at outlet of each watershed (+1 upslope control well on each farm).

• 3 or 4 piezometers in each nest – each 3.2 ft deeper than the next.• 5 stations 110 yards apart along each of two streams on Grazer 2

farm.• Nutrient balance and economic analysis of the 3 farms.

A nest of three piezometers on Grazer 2 watershed BA nest of three piezometers on Grazer 2 watershed B

Nutrient Pollution PredictionsNutrient Pollution Predictions

Predicted Mean

Annual Ground

Water Nitrate-N

(ppm)

Predicted Mean

Annual Ground

Water Nitrate-N

(ppm)

Cumulative Seasonal Stocking Rates (AD/ha)Cumulative Seasonal Stocking Rates (AD/ha)

N fertilizer

White clover

N fertilizer

White clover

From: Stout, W.L., et al. 2000. J. Soil Water Cons.:238-243

From: Stout, W.L., et al. 2000. J. Soil Water Cons.:238-243

Confined Feeding SystemsConfined Feeding Systems

High production per cow and per High production per cow and per

acre.acre. High cost per CWT milk. High cost per CWT milk.

Grow, harvest and Grow, harvest and transport crops.transport crops.

Import feed and fertilizerImport feed and fertilizer Collect, store and haul Collect, store and haul

manuremanure

Cows standing stillCows standing still

Manure on the move Manure on the move

High capital costsHigh capital costs

Capital intensive confined feeding facilityCapital intensive confined feeding facility

Sample collection• Upper 1 m of groundwater sampled biweekly.• Streams on Grazer 2 farm sampled biweekly + plus storms.Streams on Grazer 2 farm sampled biweekly + plus storms.

Groundwater Monitoring DesignGroundwater Monitoring Design

Nest ANest ANest BNest B

Nest CNest C

3 - 15 acre watershed3 - 15 acre watershed

CCB

AA

Nitrate-N Nitrate-N in groundwater under six watersheds during the study period

Nitrate-N Nitrate-N in groundwater under six watersheds during the study period

1000 1100 1200 1300 1400 1500 1600 1700Day of Century

0

10

20

30

40

50

Grazer 2Grazer 1Confined

1000 1100 1200 1300 1400 1500 1600 1700Day of Century

0

10

20

30

40

50

Grazer 2Grazer 1ConfinedDrought period (5/01-

11/02) excluded

Drought period (5/01-11/02) excluded

2003 20042002Distance weighted least squares lines

Distance weighted least squares lines

N=2700

Sample analysis• Filtered (0.25 micron) to separate particulate form dissolved nutrients.• Dissolved nitrate, ammonium and phosphate determined.• Pressurized microwave persulfate digestion used for total dissolved N

and P.

• Total N – NO3-N + NH4-N = dissolved organic N (DON)

• Total dissolved P - reactive dissolved P = dissolved organic P (DOP)

Using nests of monitoring wells (piezometers) set to different depths allowed us to sample the upper 3 ft of groundwater even as the water table fell from winter highs to summer lows.

Using nests of monitoring wells (piezometers) set to different depths allowed us to sample the upper 3 ft of groundwater even as the water table fell from winter highs to summer lows.

Confined Grazer 1 Grazer 20

3

6

9

12

Nitr

ate

-N,

mg

/L

homesteadaway

Confined Grazer 1 Grazer 20

3

6

9

12

Nitr

ate

-N,

mg

/L

homesteadaway

Confined Grazer 1 Grazer 20.01

0.02

0.03

0.04

0.05

Dis

solv

ed O

rgan

i c P

, mg/

L

homesteadaway

Confined Grazer 1 Grazer 20.01

0.02

0.03

0.04

0.05

Dis

solv

ed O

rgan

i c P

, mg/

L

homesteadaway

Nitrate-NNitrate-N Dissolved Organic PDissolved Organic P

Groundwater nutrients by proximity of watershed to barnyard

Groundwater nutrients by proximity of watershed to barnyard

0

5

10

15

N in

gro

und w

ater

, mg/

L

DONNO3-N

2002-2003

Dissolved Organic and Inorganic Nutrients in Groundwater

Dissolved Organic and Inorganic Nutrients in Groundwater

DON = 20% of Total N

DON = 20% of Total N

0.00

0.05

0.10

0.15

0.20

0.25

0.30

Dis

solv

ed P

, mg/

L

Diss Organic PDiss Reactive P

Org. P varies from 20 to 43% of Total dissolved P

Org. P varies from 20 to 43% of Total dissolved P

Note: Grazer 2 underlain by calcareous rocks that trap PNote: Grazer 2 underlain by calcareous rocks that trap P

Means of 106 to 160 samples

• We found N and P leaching under MIG pastures no higher or lower than under manured cropland on confined dairy.

• Stream water N and P did not increase as base flow crossed MIG pastures, but cattle camping area near one stream increased particulate P during storms.

• We found no reason reject MIG as an environmental Best Management Practice.

• We found N and P leaching under MIG pastures no higher or lower than under manured cropland on confined dairy.

• Stream water N and P did not increase as base flow crossed MIG pastures, but cattle camping area near one stream increased particulate P during storms.

• We found no reason reject MIG as an environmental Best Management Practice.

ConclusionsConclusions

• We found annual average NO3-N of 4 and 6 ppm in shallow groundwater for annual stocking rates of 348-810 animal days/ha – far lower that the 15 and 32 ppm predicted by monolith lysimeter research (Stout et al., 2000) for these stocking rates.

• We found annual average NO3-N of 4 and 6 ppm in shallow groundwater for annual stocking rates of 348-810 animal days/ha – far lower that the 15 and 32 ppm predicted by monolith lysimeter research (Stout et al., 2000) for these stocking rates.

Stream Water Total Nitrogen

Stream Water Total Nitrogen

1 2 3 4 5SITE

0

1

2

3

4

5

Str

ea

m w

ate

r N

, p

pm

DONNO3-N

05/01 - 02/04Storm flow, stream A

Stream Flow

1 2 3 4 5SITE

0

1

2

3

4

5

Str

ea

m w

ate

r N

, p

pm

DONNO3-N

05/01 - 02/04Base flow, stream ABase FlowBase FlowBase FlowBase Flow

Stream Flow

No increase in N as stream flows through pastureNo increase in N as stream flows through pasture

Storm FlowStorm FlowStorm FlowStorm Flow

Stream water P across grazed watersheds (means of two streams)

Stream water P across grazed watersheds (means of two streams)

Storm flowStorm flow Base flowBase flow

Flow directionFlow direction Flow directionFlow direction

0

10

20

30

40

0

10

20

30

40

Nitrate-NWater table

Day of Century

0

10

20

30

40

0

10

20

30

40

0

10

20

30

40

Nitrate-NWater table

Day of Century

0

10

20

30

40

Day of Century

Grazer 1 A

Soil surface

EPA limit

Grazer 1 B

Grazer 2 A Grazer 2 B

Confined A Confined B

0

10

20

30

40

0

10

20

30

40

Nitrate-NWater table

Day of Century

0

10

20

30

40

0

10

20

30

40

0

10

20

30

40

Nitrate-NWater table

Day of Century

0

10

20

30

40

Day of Century

Grazer 1 A

Soil surface

EPA limit

Grazer 1 B

Grazer 2 A Grazer 2 B

Confined A Confined B

Water tableWater table

Nitrate-NNitrate-N

Because of drought, only data from 10/02 – 06/04 used for statistical comparisons

Nitrate - NNitrate - N and groundwater levels under six watersheds, 05/01 – 06/04Nitrate - NNitrate - N and groundwater levels under six watersheds, 05/01 – 06/04

Intensive Grazing:Intensive Grazing:

A Threat to Water Quality?A Threat to Water Quality?

-Ray Weil, Rachel Gilker (Univ. of Md) & Bill Stout (USDA)-Ray Weil, Rachel Gilker (Univ. of Md) & Bill Stout (USDA)

• Mid-Atlantic regulators were concerned about groundwater pollution from MIG as previous research had suggested intensive grazing causes high N leaching.

• NZ and European research used high N fertilization rates (300 - 600 lb N/acre).

• Monolith lysimeters used in some research may cause artifact ponding and preferential flow patterns because simulated urine was confined to lysimeter ring.

Installing monolith lysimeters like those used for pasture leaching research in PA.

Installing monolith lysimeters like those used for pasture leaching research in PA.

Earlier research may have been flawed by potential for causing rapid leaching by preferential flow down worm channels and soil cracks. This occurs because of momentary ponding when simulated urine is confined by a lysimeter covering a much smaller area than natural urine spots.

Earlier research may have been flawed by potential for causing rapid leaching by preferential flow down worm channels and soil cracks. This occurs because of momentary ponding when simulated urine is confined by a lysimeter covering a much smaller area than natural urine spots.

Urine spots in the field

Urine spots in the field

Artifact ponding and preferential flow?

Artifact ponding and preferential flow?

Relative size

of leachin

g lysimet

er

Relative size

of leachin

g lysimet

er

Concern about nutrient pollution from MIG

Concern about nutrient pollution from MIG

Watershed AWatershed AWatershed AWatershed A

Storm flowStorm flow Base flowBase flow

Stream water P across grazed watersheds (means of 2 streams)

Stream water P across grazed watersheds (means of 2 streams)

Flow directionFlow direction Flow directionFlow direction