The full proceedings paper is at: www.extension.org/72781 Previous research conducted in western Washington State 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 a 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. The objective of this study was to characterize the effect of re-seeding of cropland using minimum tillage and conventional tillage methods on crop uptake of nitrogen, soil nitrate-N concentration, nitrate concentration in shallow ground water underlying the field, and the relationships between these matrices.

1. Fate of Manure Nitrogen Applied
for Grass Silage Production
Joe Harrison and Lynn VanWieringen,
Washington State University
Barb Carey, Washington Department of Ecology

2. 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
5
10
15
20
25
30
35
40
45
Nitrate-N(mg/L)
MCL
2004 2005 2006 2007 2008
Error Bars = +/- 1 SD
2009
Tillage

3. 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.

4. nitrification
Organic
Nitrogen
DenitrificationLeaching
Volatilization
Nitrate
NO3
-
Ammonium
NH4
+
N2 or N2O
Plant
Uptake
NH3
Ammonia
N Cycle

6. BertrandCreek
Two wells side by side—one shallow and one deep well
First three wells drilled
Study site and well locations

7. Bedrock
-700
-600
-500
-400
-300
-200
-100
0
100
200
300
400
500
0 2 4 6 8 10 12 14
Sea
Level
Sumas-BlaineSurficial Aquifer
Everson-VashonSemi-confining Unit
Feet
West East
Miles
Vertical scale greatly exaggerated
Bertrand
Creek
Study
Site

8. 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.

9. Samples of manure were taken at
each application for nutrient content
Application rate was recorded

10. Grass samples were taken just prior to
Each cutting for yield and nutrient content

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

12. 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.

13. 0
10
20
30
40
50
60
70
80
90
1st Qtr 2nd Qtr 3rd Qtr 4th Qtr
East
West
North

16. 0
10
20
30
40
50
60
70
80
90
1st Qtr 2nd Qtr 3rd Qtr 4th Qtr
East West
North
Figure 1. Soil nitrate concentrations during the study period.

17. 0
5
10
15
20
25
Averagenitrate-Ningroundwater(mg/L)

18. 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.

19. 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).

20. 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.

21. 0
10
20
30
40
50
60
70
80
90
1st Qtr 2nd Qtr 3rd Qtr 4th Qtr
East
West
North

23. 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

24. 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-

25. 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

26. 0
2
4
6
0 200 400 600 800
mbelowwatertable
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.

27. Water Table (Saturated)
Nitrate
(NO3-N-)
Atmospheric
N2 gas
Soil Nitrate
(NO3
--N)
Organic N
Ammonia
(NH4
+-N)
Nitrate
(NO3-N-)
Grass N
Harvested
Manure
Ammonia (NH4
+-N)
Organic N
Plant &
Microbial
Residues
Vadose
Zone
Groundwater
Irrigation:
Ammonia,
Total N
Ammonia
Ammonia
Soil
Organic
Matter
Inorganic
Fertilizer