soil fertility and nutrient cycling in grazed systems miguel l. cabrera crop & soil sciences...

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