soil fertility and nutrient cycling in grazed systems miguel l. cabrera crop & soil sciences...
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Soil Fertility and Nutrient Cycling in Grazed Systems
Miguel L. Cabrera
Crop & Soil Sciences University of Georgia
Topics
• Cycling of N, P, and K in pastures
• Nutrient distribution
• Soil sampling
• Soil pH and liming
• Fertilizing with urea fertilizers
• Water quality
Nitrogen
• Required in large amounts
• Bermudagrass: 110-350 lb N/acre/year
• Fescue: up to 215 lb N/acre/year
Microbial N50 lb N
Plant50 lb N
100 lb N
Soil Org N30 lb N
Inorg N20 lb N
1100 lb N fertilizer
50 lb N 50 lb N
Microbial N Plant
50 lb N
Removal with Hay
Soil Org N
20 lb NSoil Inorg.N
30 lb N
Fate of Fertilizer N in Hayed Grasslands
Treatment Management Organic N accumulation
lb N/acre/year
Hayed Monthly cuts to 2 inches
51 (23%)
Franzluebbers and Stuedemann (2009)
Organic N accumulation rate in upper 12 inchesof soil during 12 years of haying or grazing with a
yearly application of 220 lb N/acre as NH4NO3.
Microbial 50 lb N
Plant50 lb N
100 lb N 40 lb N
15 lb N
NH3 + N2O
5 lb N
NO3-
20 lb N
Org N30 lb N
Inorg N20 lb N
Org N 15 lb N
1100 lb N fertilizer
50 lb N 50 lb N
Microbial N Plant
50 lb N
Animal Intake
40 lb N Feces+Urine
Soil Org N
15 lb NNH3 + N2O
5 lb N NO3 Leaching20 lb N 5 lb NSoil Inorg.N
30 lb N 15 lb N
10 lb N
Animal body
Fate of Fertilizer N in a Grazed Grassland
Treatment Management Organic N accumulation
lb N/acre/year
Hayed Monthly cuts to 2 inches 51 (23%)
High Grazing Pressure
Maintained at 1300 lb/acre 92 (42%)
Low Grazing Pressure
Maintained at 2600 lb/acre 122 (56%)
Franzluebbers and Stuedemann (2009)
Organic N accumulation rate in upper 12 inchesof soil during 12 years of haying or grazing with a
yearly application of 220 lb N/acre as NH4NO3.
Treatment Management Organic N Accumulation
lb N/acre/year
Hayed Monthly cuts to 2 inches 78 (34%)
High Grazing Pressure
Maintained at 1300 lb/acre 174 (76%)
Low Grazing Pressure
Maintained at 2600 lb/acre 182 (79%)
Franzluebbers and Stuedemann (2009)
Organic N accumulation rate in upper 12 inchesof soil during 12 years of haying or grazing with a yearly applications of 230 lb N/acre as broiler litter.
Farm 1 Farm 2 Farm 1 Farm 2
------------kg N yr-1 ----------- % of Total N input
N input
Mineral Fertilizer
60,395 33,807 78.9 40.7
Grain Feed 11,959 43,680 15.6 52.6
Maize Silage 1,224 0 1.6 0
Hay 3,011 5,587 3.9 6.7
Total Inputs 76,589 83,074 100 100
N output
Milk 12,066 14,218 15.8 17.1
N2O emission 2,032 N/A 2.7 N/A
NH3
volatilization
4,067 3,052 5.3 3.7
NO3 Leached 205 4,364 0.3 5.3
Total Outputs 18,370 17,270 24 21
N remaining 58,219 65,804 76 79
Take-home Message for N
• Hayed Systems:• 20 to 35% of applied N builds up soil organic N
• Grazed Systems:• 40 to 75% of applied N builds up soil organic N
Phosphorus
• Required in lower amounts than N
• Bermudagrass: 25 to 75 lb P/acre/year
• Fescue: 10 to 15 lb P/acre/year
Soil 80 lb P
Plant 20 lb P
100 lb P
1100 lb P fertilizer
80 lb P 20 lb P
Soil PPlant
20 lb P
Removal with Hay
Org + Inorg P
80 lb P
Fate of Fertilizer P in Hayed Grasslands
Soil 80 lb P
Plant 20 lb P
100 lb P 16 lb P
16 lb P
1100 lb P fertilizer
80 lb P 20 lb PSoil P Plant
20 lb P
Animal Intake
16 lb P Feces+Urine
Soil Org+Inorg P
80 lb P
4 lb P
Animal body
Fate of Fertilizer P in a Grazed Grassland
Take-home Message for P
• Hayed Systems:• 80% of applied P builds soil P
• Grazed Systems:• 95% of applied P builds up soil P
Potassium
• Required in similar amounts as N
• Bermudagrass: up to 480 lb K2O/acre/year
• Fescue: up to 250 lb K2O/acre/year
Soil 10 lb K
Plant 90 lb K
100 lb K
1100 lb K fertilizer
10 lb K 90 lb KSoil K
Plant
90 lb P
Removal with Hay
Inorg K
10 lb K
Fate of Fertilizer K in Hayed Grasslands
Soil 10 lb K
Plant 90 lb K
100 lb K 80 lb K
1100 lb K fertilizer
10 lb K 90 lb KSoil K
Plant
90 lb K
Animal Intake
80 lb K Feces+UrineSoil Inorg K
10 lb K
10 lb K
Animal body
Fate of Fertilizer K in a Grazed Grassland
Take-home Message for P
• Hayed Systems:• 10% of applied K builds up soil K
• Grazed Systems:• 90% of applied K builds up soil K
Topics
• Cycling of N, P, and K in pastures
• Nutrient distribution
• Soil sampling
• Soil pH and liming
• Fertilizing with urea fertilizers
• Water quality
0.90 lb N
Average N, P, and K Returned in Feces and Urine (lb nutrient/cow/day)
0.45 lb urine
0.45 lb feces
450-600 lb N/a
1100-1800 lb N/a
0.40 lb K
0.3 lb urine
0.10 lb feces
300-400 lb K/a
240-400 lb K/a
0.15 lb P
0.02 lb 0.13 lb
urine50-80lb P/a
feces130-170 lb P/a
Nutrient Distribution in Pastures
• 66 x 40 feet• 2 round bales fed• 6.5 cows/acre for• 4 months
lb inorg. N/acrein upper 6 inches
Jungnitsch (2008)
Temperature-Humidity Index
Franklin et al. (2009)
Pasture-based dairy in western Virginia.Pasture-based dairy in western Virginia.
Manure Distribution
Manure Distribution
Rotation Frequency
Years to Get 1 Pile/sq. yard
Continuous 27
14 day 8
4 day 4 – 5
2 day 2
Improving Nutrient distribution
•Rotational grazing in small square paddocks•Short grazing periods•Trough in each paddock•Minerals away from troughs and shade•Alternating feeding locations•Feeding locations in low fertility zones
Topics
• Cycling of N, P, and K in pastures
• Nutrient distribution
• Soil sampling
• Soil pH and liming
• Fertilizing with urea fertilizers
• Water quality
• Auger, probe, spade.• Discard organic duff.• Sample to 4 inches.• Collect samples in clean, plastic container.• Mix, remove debris, subsample if necessary.
Soil SamplingSoil Sampling
Sampling is Critical
• A soil test is no better than the soil sample submitted for analysis.
• Sampling error is the most common source of error in soil test results.
• The goal of soil sampling is to obtain a representative sample for each paddock.
Sample Individual Paddocks
Courtesy: Univ. of Missouri Extension
Field Average Sampling
One Core
Random Composite Sample Random Composite Sample
One average Soil Test level
• Take 20-40 random samples for each 10 acres.• Avoid areas near shade, troughs, trails.
Topics
• Cycling of N, P, and K in pastures
• Nutrient distribution
• Soil sampling
• Soil pH and liming
• Fertilizing with urea fertilizers
• Water quality
Soil pH and Liming
• Sources of soil acidity
• Measuring soil pH
• Problems in acid soils
Sources of Soil Acidity
Acids in Precipitation H2O + CO2 H2CO3 H+ + HCO3
-
- H2SO4 and HNO3
- Rainfall pH < 4.3 in many industrial areas
Man-Made Causes of Acid Rain
• Exhaust from cars, trucks, and buses
• Power plants that burn coal
• Pollution from industry
Sources of Soil Acidity
Nitrogen Transformations
Nitrification:
NH4+ NO3
- + 2H+
Ammonium Nitrate Hydrogen Ions
Ammonia Volatilization:
NH4+ NH3 + H+
Ammonium Ammonia Hydrogen Ion
Measuring Soil pH
• Salts:• decrease soil pH (negatively charged soils)
Water 0.01 M CaCl2
January July December
5.3
5.9
Fertilizer and manure application, average Georgia soil
ΔpHaverage = 0.6
pHw
pHCaCl2
Measuring soil pH
The UGA method for measuring pH avoids the seasonal variation in pH caused by differences in
the soil’s salt content.
Equivalent water pH = pH in 0.01 M CaCl2 + 0.6
0
20
40
60
80
100
120
3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0
Soil pH (1:1) CaCl2
KC
L E
xtr
. A
L (
mg
/kg
)
Problems in Acid Soils
Miller et al. (2003)
Critical pH = 4.85
Equivalent Water pH = 5.45
Applications of lime every 3 to 4 yearsare needed inSoutheastern soils tomaintain appropriatechemical balances inthe soil.
Nutrient Availability as Affected by pH
Topics
• Cycling of N, P, and K in pastures
• Nutrient distribution
• Soil sampling
• Soil pH and liming
• Fertilizing with urea fertilizers
• Water quality
Fertilizing with Urea Fertilizers
Source: H. Vroomen -TFI, and AAPFCO
Ammonia Losses in Spring 2006
Days after application
NH
3 lo
ss (
% o
f ap
plie
d N
)
0
10
20
30
40
50
10
20
30
40
50Nitamin® UAN Urea
0.1
0.2
0.3
0.4
Soi
l wat
er c
onte
nt (
g g-1
)
20 40 80
Rai
nfal
l (m
m)
60
Rainfall
Soil water content
Ammonia Losses in Spring 2005
Days after application
NH
3 lo
ss (
% o
f ap
plie
d N
)
0
10
20
30
40
50
10
20
30
40
50 Nitamin® UAN Urea
0.1
0.2
0.3
0.4
Soi
l wat
er c
onte
nt (
g g-1
)
20 40 60
Rai
nfal
l (m
m)
Rainfall
Soil water content
Ammonia volatilization losses under field conditions
Fertilizer
--------------- Ammonia loss (% of applied N) -----------------
Fall 2004
Urea
UAN
Nitamin®
19 a*
6 b
6 b
Spring 2005
12 a
13 a
14 a
•Within a column, values followed by the same letter are not significantly different according to Fisher’s LSD at p=0.05
Fall 2005 Spring 2006
46 a
33 b
34 b
24 a
18 a
18 a
Hornbeck et al (2010)
Hornbeck et al (2010)
Topics
• Cycling of N, P, and K in pastures
• Nutrient distribution
• Soil sampling
• Soil pH and liming
• Fertilizing with urea fertilizers
• Water quality
Water Quality
• Avoid applications between Nov and March• Provide off-stream water (troughs)• Restrict access to riparian areas• Provide stream crossings
Ru
no
ff D
RP
(m
g P
L-1
)
0
5
10
15
20
J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N
Ru
no
ff V
olu
me
(m
m)
0
20
40
60
80
1998199719961995
Avoid applications between November and March
Stream Crossing
Before
After
Dif
fere
nce
s in
To
tal P
(m
g L
-1)
-1
0
1
Dif
fere
nce
s in
Fec
al C
olif
orm
s (C
FU
100
mL
-1)
-5.0e+4
0.0
5.0e+4
1.0e+5
1.5e+5
2.0e+5
2.5e+5
Dif
fere
nce
s in
Dis
solv
ed R
eact
ive
P (
mg
L-1
)
-2
-1
0
1
2
Pre-fencing Post-fencing
a)
b)
c)
Thomas et al. (2000)
Differences in phosphorusand E.coli between streamin crossing and controlstream before and afterinstallation of streamcrossing.
SUMMARY• Grazing animals return 80-90% of N, P, and K• Nutrient distribution can be improved by:
• Rotational grazing (small paddocks)• Water troughs• Feed and salt locations
• Proper soil sampling is critical• Soil pH should be maintained by liming• Losses of ammonia from urea can be reduced by 0.5 inches of rain or irrigation• Water quality can be improved by:
• Avoiding applications from Nov-Mar• Providing water troughs• Limiting access to riparian areas