Fate of Manure Nitrogen Applied

for Grass Silage Production

Joe Harrison and Lynn VanWieringen,

Washington State University

Barb Carey, Washington Department of Ecology

Previous research conducted in western Washington has demonstrated that when manure N is applied at rates greater than needed for grass uptake, excess N in soil in the form of nitrate-N can leach to shallow groundwater during the months of high rainfall.

In the prior study, it was evident that tillage and reseeding of the cropland was a contributor to loss of nitrate–N from soil to underlying groundwater.

0

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Nit

rate

-N (m

g/L)

MCL

2004 2005 2006 2007 2008

Error Bars = +/- 1 SD

2009

Tillage

Objectives

Characterize nitrogen inputs, outputs and underlying GW nitrate concentration in a typical manured field over the aquifer.

Propose adjustments in management practices to minimize nitrogen leaching.

Purpose

A two- year study was initiated in 2009 to study the fate and transport of nitrogen from dairy manure when applied to cropland that was reseeded to grass for silage production.

nitrification

Organic Nitrogen

Den

itri

fic

ati

on

Lea

ch

ing

Vo

lati

lizati

on

Nitrate

NO3-

Ammonium

NH4+

N2 or N2O

Plant

Uptake

NH3

AmmoniaN Cycle

Bert

rand C

ree

k

Two wells side by side—one shallow and one deep well

First three wells drilled

Study site and well locations

Bedrock

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-500

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-200

-100

0

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300

400

500

0 2 4 6 8 10 12 14

Sea Level

Sumas-Blaine Surficial Aquifer

Everson-Vashon Semi-confining Unit

Feet

West East

MilesVertical scale greatly exaggerated

Bertrand Creek

StudySite

One-half of a 22- acre grass field was prepared with

conventional tillage, and one-half was prepared with

minimum tillage in May of 2009.

Samples of manure were taken at each application for nutrient content

Application rate was recorded

Grass samples were taken just prior toEach cutting for yield and nutrient content

Temperature, pH, dissolved oxygen, and conductivity are measured in a flowCell assembly before the water is exposed to the atmosphere.

Tillage and Harvest

In 2009, after the grass was reseeded, the

conventional till grass was harvested 2 times,

and the minimum till grass was harvested 3

times.

Due to a poor stand establishment, the

minimum till area received minimum till

treatment again in 2010.

In 2010, the conventional till grass was

harvested 4 times and the minimum till grass

was harvested twice.

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1st Qtr 2nd Qtr 3rd Qtr 4th Qtr

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West

North

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1st Qtr 2nd Qtr 3rd Qtr 4th Qtr

East West

North

Figure 1. Soil nitrate concentrations during the study period.

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Ave

rag

e n

itra

te-N

in

gro

un

dw

ate

r(m

g/L

)

Summary

There was no evidence of a difference in

groundwater nitrate due to the tillage

treatment.

Results from this case study indicated that

the type of tillage had an impact on the

timing of increases in soil nitrate.

However, variability in denitrification

conditions in monitoring wells obscured

comparison of groundwater nitrate effects

between the two management practices.

Nitrogen Application and Harvest

Total nitrogen applied for minimum till

and conventional till, respectively,

were: 523 and 440 lbs/acre (2009),

and 697 and 697 lbs/acre (2010).

Total nitrogen harvested for minimum

till and conventional till respectively,

were: 310 and 298 lbs/acre (2009),

and 425 and 477 lbs/acre (2010).

Soil Nitrate

Soil nitrate-nitrogen for the minimum

till plot remained below 30 ppm in

2009 except on one occasion. Soil

nitrate for the minimum till plot was

observed to increase to 40 and 60

ppm in 2010.

Soil nitrate-nitrogen for the

conventional till plot increased to 60

ppm in 2009, and 35 ppm in 2010.

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90

1st Qtr 2nd Qtr 3rd Qtr 4th Qtr

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North

Nitrogen Mass Balance

Inputs Outputs

Manure

Fertilizer

Irrigation water

Atmospheric input

Soil organic matter

Grass crop

Volatilization

Denitrificatio

n

Residual

• Soil nitrate

• Groundwater

nitrate

• Soil ammonium

• Soil organic matter

Root Zone

Water Table (Saturated)

Unsaturated Zone

Manure (Ammonia, Organic N)

NO3-N-

N2 gas

denitrification

NO3-N-

Organic N

Some mineralizes

NO3-N-

Summer

NH4-N

NO3-N-

Water Table

Root ZoneNO3-N

Fall-Winter Precipitation/Recharge

(10-30 inches/year in US portion of the aquifer)

Organic N

N2 gas

denitrification

Winter

NO3-N

0

2

4

6

0 200 400 600 800

m b

elo

w w

ate

r ta

ble

Farm A Farm B Farm C

1 year since recharge

2 years since recharge

3 years since recharge

Groundwater recharged under Farm

B 2 years ago

Groundwater recharged under 4 to 6 farm fields upgradient 3 years ago

Distance(meters)

Vadose zone

(Adapted from Ryan, 2008)

Water Table

Generalized groundwater flow beneath fields in the Abbotsford area 8 miles

northeast of the study site showing that water near the top of the water table

represents the most recent water recharged from above.

Water Table (Saturated)

Nitrate(NO3-N-)

Atmospheric N2 gas

Soil Nitrate(NO3

--N)

Organic N

Ammonia(NH4

+-N)

Nitrate(NO3-N-)

Grass N Harvested

ManureAmmonia (NH4

+-N)

Organic N

Plant & Microbial Residues

Vadose Zone

Groundwater

Irrigation: Ammonia, Total N

Ammonia

Ammonia

Soil Organic Matter

Inorganic Fertilizer