The full proceedings paper is at: www.extension.org/72842 Of the total nitrogen (N) consumed by dairy cows on confinement farms (cows fed in barns), a general range of 20% to 35% is secreted in milk and the remaining N is excreted in manure. The N contained in manure is either recycled through crops after field application, or lost to the environment. To better understand the synergistic nature of feed N and manure N management and environmental N loss from dairy farms, a series of cow, laboratory and field experiments (Figure 1) was undertaken to quantify the relative amounts of N contained in individual ration components that are secreted in milk, excreted in urine and feces, taken up by crops after manure application to soil, and lost as ammonia (NH3) and nitrous oxide (N2O) from dairy barns and soils.

1. How much of the nitrogen contained in dairy ration
components is partitioned into milk, manure, crops
and environmental N loss?
J. M. Powell, T. Barros, M.A.C. Danes, M.A. Aguerre and M.A. Wattiaux
USDA-ARS, US Dairy Forage Research Center, Madison, Wisconsin, USA
Dept. Dairy Science, University of Wisconsin, Madison, Wisconsin, USA
Waste-to-Worth Conference
Seattle WA
March 30 to April 3, 2015

2. Typical ration fed to cows
(confinement dairy farms)
Forage
Grain
Protein
Supplement
Minerals
Vitamins
Protein supplements
impact
• Feed N use efficiency
• Milk protein and milk urea
• Fecal N: Urinary N ratio
• Urea N in urine
• Ammonia emissions
• Nitrous oxide emissions
• Fecal N mineralization in soil
• Plant N uptake

3. How much of the nitrogen
in ration components
is partitioned into:
• Milk
• Manure
(and after manure excretion)
• Crops
• N loss
Today’s study

4. AS = Alfalfa silage
CS = Corn silage
CG = Corn grain
SB = Soybean SBM = Soybean meal
15NAS
15NAS, CS, CG, SBM 15NAS milk
15NAS urine
15NAS feces
15NCS AS, 15NCS, CG, SBM 15NCS milk
15NCS urine
15NCS feces
15NCG AS, CS, 15NCG, SBM 15NCG milk
15NCG urine
15NCG feces
15NSB AS, CS, CG, 15NSBM 15NSBM milk
15NSBM urine
15NSBM feces
15NFertilizerappliedtocropsinfield
15Nurine and
15Nfeces
applied to
barn floors
and soils to
determine
ration
components’
contribution
to NH3, NO3,
N2O and
crop N
uptake
Component
15Nlabeling
Feed 15N
in TMRs
15N in milk,
urine, feces
15N manure
transformations
3 cows
3 cows
3 cows
3 cows
15N transformations being studied

5. feeding 15N
in TMRs
feces
urine
collection

6. What was fed
Ration
component
% DMI NDF
(g/kg DM)
TN
(g/kg DM)
15N
(atom %)
Alfalfa silage 32.5 443 29.8 0.730
Corn silage 31.2 448 11.3 1.857
Corn grain 20.1 88 11.8 2.040
Soybean meal 13.5 92 78.0 1.385
Minerals 2.7 - - -
Corn
silage
Corn
grain
Alfalfa
silage
Soybean
meal
minerals

7. Feed intake, milk and manure production of 12 cows
fed 15N and 14N ration components as TMRs
Parameter Min Max
DMI (kg/cow/d) 22.8 23.6
NI (g/cow/d) 591 613
Milk (kg/cow/d) 24.8 28.5
FNUE (%) 22.1 25.0
Urinary N (g/cow/d) 231 233
Urea-N (g/cow/d) 175 193
Fecal N (g/cow/d) 154 174
How cows responded
to what was fed

8. 15N secretion in milk
15N excretion in feces and urine
Begin
15N TMR
Begin
14N TMR

9. Modeling
15N recovery
Milk
Urine
high
lowhighlow
Feces

10. Mixing feces and urine
15N manure
application
and tillage

11. 15N manure
applied to
corn
Total
manure N
applied
Atom %
15N in
manure
(g/m2)
Alfalfa silage 28.9 0.514
Corn silage 30.7 0.490
Corn grain 34.7 0.455
SB meal 29.0 0.499
15N manure
applied to corn for silage

12. Corn silage uptake
of 15N manure
0
10
20
30
40
50
Alfalfa
silage
Corn
silage
Corn
grain
Soybean
meal
%ofmanure15Napplied
Manure 15N applied
33.4 ab
30.5 b
34.7 ab
38.1a
1st year corn 15N uptake 2nd year corn 15N uptake

13. Next steps
• Analyze 15N in urinary urea
and fecal fiber
(proxies for feed N use by cows)
• Apply 15N feces and urine
to barn floors and soil,
then measure 15N in
NH3, NH4
+, NO3
-, N2O,
plant N