Potential nitrification activity and abundance of nitrifying bacteria in beef cattle feedlot soils
Daniel N. Miller1 and Bryan L. Woodbury2; 1SWCRU, Lincoln, NE and 2MARC, Clay Center, NE; E-mail: [email protected]
Nitrification-Denitrification
NH4+ + O2 → NO2- + O2 → NO3NO2- or NO3- + Org C → CO2 + N2
Feed bunk & concrete apron
Water trough
Feed bunk sample site
Slope
Central mound
Mound sample site
Wind break
Down gradient sample site
Potential nitrifying activity,
nmol gm-1 dry soil hr-1
AOB,
log MPN gm-1 dry soil
ƒ USDA-ARS research feedlot at the U.S.
MARC, Clay Center, NE.
ƒ Dirt feedlot, 6000 head capacity.
ƒ Single feedlot pen (30 x 90 meters)
containing 62 to 74 animals.
ƒ Samples collected every two to four
weeks from Sept 1999 to May 2000.
ƒ Three depths (unconsolidated surface
material [USM], 0-10 cm, and 10-20 cm)
at three sites:
Feedbunk Site
1200
1000
800
600
400
200
0
NOB,
log MPN gm-1 dry soil
Study Site
Temporal Trends
Mound Site
Down Gradient Site
USM
0-10 cm
10-20 cm
Nitrification Activity
d
400
300
b
200
ab
100
ab
ab ab
0
NOB
10
8
c
6
a
a
ab
c
bc bc
ab
a
4
2
c
8
-1
500
AOB
10
USM
0-10 cm
10-20 cm
c
bc
b
6
a
b
a
a
a
4
2
ab
ab
a
t
unk ound adien
db
M
r
ng
Fee
w
Do
0
t
unk ound adien
db
M
r
ng
Fee
w
Do
0
t
unk ound adien
db
M
r
e
ng
Fe
w
Do
Correlations with Environmental Factors
10
8
6
Nitrifying
activity
4
Nitrifying
activity
2
0
10
8
AOB
0.344*
NOB
0.459*
Denitrifying
activity
Soil
Temp
Soil
Water
0.300*
-0.036
-0.051
0.183
-0.160
0.053
0.133
0.298*
0.258†
0.102
0.263†
-0.211
-0.109
0.010
0.215
0.172
0.230
-0.289*
-0.040
0.086
AOB
NOB
0.344*
0.459*
0.762*
0.358*
0.762*
pH
NH4+
%OM
%N
Values in red are significant at the 0.05 level. Values in purple are significant at the 0.1 level.
6
4
2
0
9/99 11/99 1/00 3/00 5/00
600
AOB, log MPN gm-1
ƒ Ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing
bacteria (NOB) by most probable number (Schmidt and
Belser, 1994).
ƒ Nitrifying potential determined by short-term assay (<4 hours)
using sodium chlorate inhibitor (Schmidt and Belser, 1994).
ƒ Statistical analysis with SAS.
Nitrification activity, nmol gm-1 hr-1
ƒ Dominant feedlot N pathway:
Urea → NH4+ → NH3
ƒ Up to 50% of excreted N lost as NH3, but
total N loss up to 70%.
ƒ What other N pathways important?
Comparisons Between Sites/Depths
NOB, log MPN gm
Methods
Problem
9/99 11/99 1/00 3/00 5/00
9/99 11/99 1/00 3/00 5/00
ƒ Regression with date and date2 by site and depth indicated
only NOB at the mound site (0-10 cm depth) or NOB at the
down gradient site (0-10 and 10-20 cm depth) were related
to time (P < 0.02).
Conclusions
¾ Nitrifying microorganisms are present at high densities within
cattle feedlot soils.
¾ Although seasonal effects were minimal, spatial differences
were observed in the activity and distribution of nitrifying
microorganisms.
¾ Correlations between nitrifier abundance, potential activities,
and environmental factors indicate that soil temperature, pH,
and ammonium may influence nitrifiers in the feedlot soil.
References
Schmidt, E.L. and L.W. Belser.
1994. Autotrophic nitrifying bacteria.
In: Weaver, R.W. et al. Methods of
Soil Analysis Part 2 Microbiological
and Biochemical Properties. Soil
Science Society of America,
Madison, WI.
Woodbury, B.L. et al. 2001.
Seasonal and spatial variations of
denitrifying enzyme activity in
feedlot soil. Trans ASAE 44:1635.