2010 Georgia Grazing School:
Soil fertility and nutrient cycling in grazing systems
2010 Grazing School for Milk Producers
Soil fertility and nutrient cycling in
grazing systems
Dennis Hancock
Extension Forage Specialist
UGA – Dept. of Crop and Soil Sciences
“What’s in the soil, is in the plant,
is in the animal, ….”
Plant Nutrients
Liebig’s Law of the Minimum
Macro- (Primary)
Micro- (Trace)
Element
Available Form
Element
Available Form
Oxygen
O2, OH-
Iron
Fe+2 , Fe+3
Carbon
C03-2,
Copper
Cu+2
Hydrogen
H+, OH-
Zinc
Zn+2
Nitrogen
NO3- , NH4+
Manganese
Mn+2 , MnO4-
Phosphorus
HPO4-2, H2PO4-
Molybdenum
HMoO4- , MoO4-2
Potassium
K+
Boron
H3BO3, B4O7-2
Chlorine
Cl-
HCO3 , CO2
,
S Mo
Cu
Zn
Mn
P
Fe
Cl
Cu+
B
Mg
Ca
K
N
Meso- (Secondary)
Element
Available Form
Calcium
Ca+2
Magnesium
Mg+2
Sulfur
SO4-2
Soil Test Ranges
Soil Test and Follow Fertility
Recommendations
Sample hay and crop fields every year and
1/3 of your paddocks each year.
Phosphorus
Potassium
Low
0-30
0-60
Calcium
Low
0-200
Magnesium
Low
0-30
Med
31-60
61-150
High
61-100
151-250
V. High
101+
250+
Adequate
201+
Med
31-60
High
61+
Coastal Plain
Dr. Dennis Hancock
Extension Forage Agronomist
1
2010 Georgia Grazing School:
Soil fertility and nutrient cycling in grazing systems
Costs Increase When Soil Fertility
Decreases
“All Kinds of Wacky”
Price
($/lb of N, P2O5, or K2O)
1.00
Let’s assume P & K have been equally taken care of or equally neglected.
So, let’s consider bermudagrass fertility.
Ammonium nitrate (now Urea)
Triple-Super-phosphate (46%)
Potassium chloride (60%)
0.80
Recommended Rate of
P&K
Fertility
0.60
N
P2O5
K2O
------------- (lbs/acre) -------------
0.40
0.20
($/acre)
V. High
250
0
0
125
High
250
30
150
201
Medium
250
60
200
233
Low
250
80
250
262
10
09
20
08
20
07
20
06
20
05
20
04
20
03
20
02
20
01
20
00
20
99
20
98
19
97
19
96
19
19
19
95
0.00
Total
Cost
Assumptions: Using 28% UAN ($280/ton), DAP ($500/ton), and Muriate
of Potash ($525/ton).
The False Economy of Shortcuts
Pasture Cost ($/lb) =
Cost of Production Compared to Average
Total Cost ($/Acre)
Forage Yield (lbs/Acre)
Yield
130%
120%
110%
100%
90%
80%
70%
€
Get your priorities right!
Maintaining soil pH
is job #1.
•  Nutrient availability
•  Soil structure
•  Soil biological activity
•  Aluminum toxicity
Dr. Dennis Hancock
Extension Forage Agronomist
2
70% 80% 90% 100% 110% 120% 130%
54
62
69
77
85
92
100
58
67
75
83
92
100
108
64
73
82
91
100
109
118
70
80
90
100
110
120
130
78
89
100
111
122
133
144
88
100
113
125
138
150
163
100
114
129
143
157
171
186
2010 Georgia Grazing School:
Soil fertility and nutrient cycling in grazing systems
How Soil pH Affects Availability of Plant Nutrients
Get at the Root of a Problem:
Soil pH Problems
The difference of a soil pH of 5.6 vs. 6.2:
Nutrient
Amt. Used
Annually
Unit
Price
Dec. in
Efficiency
Value of
Decrease
(Lbs/acre)
($/lb)
N
P2O5
300
60
$0.50
$0.43
35%
50%
($/acre)
-$53
-$13
K2O
250
$0.46
10%
Total
-$12
-$78
Low Soil pH = Aluminum
Toxicity
How Soil Holds Nutrients
Soil Particle
Organic Matter
K+
2+
K+ MgK
+2+Ca2+
Mg2+
+
Ca2+2+Ca
K+ Mg
Mg2+
2+ + +K
Mg
2+
+
2+
Mg
2+
K
Mg KK+ +CaMg
Ca
2+2+ K
Ca
+2+ 2+ 2+
Mg
Mg
K
2+ 2+
+ +2+K
Ca2+
2+
2+
K
2+Ca
MgMg
KCa
2+
Mg
Ca
2+
Mg
2+
Ca
+
Mg
2+
+
+
2+
Ca
2+
K
Mg
2+2+ K
Mg
Ca2+KCa
2+
Mg
2+ Ca
+ + 2+K+
MgMg
2+K
2+
Ca Mg
K+Mg2+
CaK
Ca
+ 2+
Ca2+
2+Ca
K+2+K
Mg2+
Ca2+Ca
2+
+
K Mg Ca2+
K+
Ca2+
Ca2+
K+
Mg2+
K+
Al3+
Mg2+
Ca2+
e.g., CEC = 10
Soil Acidity and CEC
K+
Ca2+
K+
BS = 100%
CaCO3
pH = 4.5
Ca2+ + CO3
Al3+
Soil
H+
Al3+
Al3+
BS = 0%
Strength of cations:
Al3+ > H+ > Ca2+ > Mg2+ > K+
pH = 5.4
Dr. Dennis Hancock
Extension Forage Agronomist
3
Al3+
Mg2+
H+
Ca2+
Soil
H+
Mg2+
K+
H+
H+
Ca2+
H+
H+
Mg2+
BS = ~ 50%
3
Soil
pH = 6.0
Ca2+
Ca2+
Mg2+
Ca2+
Ca2+
Mg2+
Ca2+
CaCO
Soil
Soil
pH = 7.0
e.g., CEC = 200
Al3+
K+
Al3+
Ca2+
H+
Ca2+
CO2 and Al(OH)3
pH = 6.5
+
2010 Georgia Grazing School:
Soil fertility and nutrient cycling in grazing systems
Use of Urea-Based Products
Nitrogen Use
• Without AN, users of N
face risky alternatives.
  NH3 volatilization loss
Ammonium Nitrate
Urea
• Urease is abundant in
thatch & organic layers
NBPT
  High N use in hay.
Polymer
Coating
• Enhanced Efficiency N
Fertilizer Products may
reduce volatilization loss
  Urease inhibition
  Encapsulate & release
maleic-itaconic
co-polymer
N Loss to Volatilization
+ H20
Urea
Ammonia
Farm A
AN
Farm B
34-0-0
urease
32%
+
Ammonium
12.5%
Nitrate
Eason, N. M.S. Thesis. 2010.
Ammonia Volatilization Trap Data
Additional Data
(ppm) Ammonia (NH4-­‐N) Vola0liza0on 2008-2009 (avg. over two locations)
2008 140 Agrotain Treated Urea
2009 as compared to urea applied in the same
way (averaged over 4 site-yrs):
120 •  Reduced ammonia volatilization by
over 63%.
•  Produced 11% more forage yield.
•  Recovered 19% more of the applied N.
•  Did not substantially affect crude
protein content.
•  Did not substantially affect the risk of
nitrate toxicity.
100 80 60 40 20 0 Urea ATU NSN ESN CON Dr. Dennis Hancock
Extension Forage Agronomist
4
2010 Georgia Grazing School:
Soil fertility and nutrient cycling in grazing systems
Another Fertilization Trick
Nitrogen Response:
Rules of Thumb
Split Your Nitrogen Applications!
Forage Type
N Response Above Critical Level*
Early Season Mid-Season Late-Season
------- lb of DM/lb of N added -------
•  Long-term, this can increase yields by 5-10% and
increase NUE by 25-30%
  Especially important under extremes
  Leaching
  Volatilization (in the case of urea-based products)
  Late freeze
  Drought
Nitrogen Response
lbs of DM/lb of N
5
10
15
20
25
30
35
40
45
50
55
$0.150
$0.075
$0.050
$0.038
$0.030
$0.025
$0.021
$0.019
$0.017
$0.015
$0.014
20-35
Tifton 85 bermuda
30-40
45-55
30-40
Annual ryegrass
5-12
10-20
15-30
N fertilization above ~40, 50, or 25 lbs of N/acre for Coastal, Tifton 85,
and ryegrass, respectively.
Corn
$/bu
$/lb
Corn Silage
$/dry ton
$/lb
Ryegrass Baleage
$/dry ton
$/lb
T85 Hay
$/dry ton
$/lb
Cost of N, $/lb of N
$0.60
$0.75
$1.00
N Cost of Additional Production
$0.120
$0.060
$0.040
$0.030
$0.024
$0.020
$0.017
$0.015
$0.013
$0.012
$0.011
35-45
Value of the Substitute
--------------------------- $/lb of DM ---------------------------
$0.100
$0.050
$0.033
$0.025
$0.020
$0.017
$0.014
$0.013
$0.011
$0.010
$0.009
30-45
*
Cost Implications of Different
Nitrogen Response Rates
$0.50
Coastal bermuda
$0.200
$0.100
$0.067
$0.050
$0.040
$0.033
$0.029
$0.025
$0.022
$0.020
$0.018
Another Fertilization Trick
$4.00
$0.071
$4.50
$0.080
$5.00
$0.089
$7.00
$0.125
$45
$0.023
$50
$0.025
$60
$0.030
$75
$0.038
$130
$0.065
$150
$0.075
$170
$0.085
$200
$0.100
$100
$0.050
$120
$0.060
$140
$0.070
$175
$0.088
K is for Persistence
Apply P in late summer or fall.
Not Competitive
Leafspot Diseases
Poor Winterhardiness
Grows Very Slow
Poor Stress Tolerance
The Stand is Gone!
Dr. Dennis Hancock
Extension Forage Agronomist
5
2010 Georgia Grazing School:
Soil fertility and nutrient cycling in grazing systems
Another Fertilization Trick
K is the Key to a Good Stand
Split Your Potassium Applications!
40-50%
in the Spring
50-60%
in mid – late season
Tissue Sampling
Troubleshooting
6 in.
K and Nutrition for Late
Gestation and Close-Up Cows
Chicken Litter
Makes Good Fertilizer…
Dr. Dennis Hancock
Extension Forage Agronomist
6
2010 Georgia Grazing School:
Soil fertility and nutrient cycling in grazing systems
Poultry Litter - Disadvantages
Variability in Chicken Litter
•  Weed pressure does increase
•  “Book Number”
  Not a source of weed seed
  Changes the fertility and makes
broadleaf weeds more competitive.
  3-3-2
•  Range in % N
•  Potassium fertilization may not be
adequate
  1.1 – 4.9%
  Poultry Litter: 3-3-2
  Ideal bermudagrass fertilizer: 5-1-4
•  Range in % P2O5
  0.9 – 4.8%
•  May result in excessive sulfur levels
•  Range in % K2O
  Some evidence for a link to copper
deficiency in cattle.
  1.2 – 4.0%
Source: Univ. of Ark. Ext. Bulletin FSA-8000.
The Value of Litter
The Value of Litter
Pre 2005 Prices
-  60 # PAN x .28 x .5 = 8.40
-  60 # P2O5 x .22 x .8 = 10.56
Other Nutrients ?
Organic Matter ?
Liming ?
Nematode Suppression ?
3-3-2
-  40 # K2O x .12 x .8 = 3.84
3-3-2
–  Total = $22.80
2010 Prices
-  60 # PAN x .50 x .5 =
15.00
-  60 # P2O5 x .43 x .8 =
20.64
-  40 # K2O x .44 x .8 =
14.08
–
Total = $ 49.72
Too much of a good thing?
Benefits of Rational Grazing
1.  Better utilization of forage
2.  Growth rate of forage is optimized
  Kept in linear/exponential growth phase
  Higher yield of forage
3.  Higher stocking rates
4.  More animal gains/milk production per acre
5.  Reduced feeding of conserved forage or
supplements
6.  Better persistence of desirable forages
  Especially clover and legume species
7.  Better weed suppression
8.  Better manure distribution
Dr. Dennis Hancock
Extension Forage Agronomist
7
2010 Georgia Grazing School:
Soil fertility and nutrient cycling in grazing systems
Nutrient Distribution in
Continuously Grazed Pastures
Manure Distribution
Manure Distribution
Rotation
Frequency
Years to Get
1 Pile/sq. yard
Continuous
27
14 day
Efficiency of Four-legged Manure Spreaders
White et al., 2001 J. Environ. Qual. 30:2180–2187
13:06
Dr. Dennis Hancock
Extension Forage Agronomist
8
8
4 day
4–5
2 day
2