assessing soil biological activity as an indicator of …sarc.calpoly.edu/pdfs/events/2017 field...

Alan FranzluebbersEcologist, Raleigh NC

Assessing Soil Biological Activityas an Indicator of Soil Health

The problem

$N2O

Fossil-fuel energy

The reality

Available Nitrogen (kg ha-1)

RelativeYield

(fraction)

0.0

0.2

0.4

0.6

0.8

1.0Assume 200 bu/a corn- grain with 1.5% N = 168 lb N/a- stover with 1.0% N = 112 lb N/a- total N need is 280 lb N/a

From 412 samples in NC- inorganic N = 57 + 78 lb N/a (0-12” depth)

Might assume the difference would be from inorganic fertilizer input

- organic N = 4532 + 2877 lb N/a

Nitrogen availability to cropsFertilizer –>

.Surface-soil inorganic N

.

Surface

1’ depth

2’ depth

3’ depth

4’ depth

.

.

.

.

.Deep-profile

residual inorganic N......

Mineralizable nitrogen

a.ka. biologically active nitrogen

Loss mechanismsRunoffLeachingVolatilizationDenitrification

Limits to availabilitySoil temperatureSoil moistureRoot accessibilityBinding to claysBinding to organic matter

Additional inputsBiological N fixationCompostPrecipitation / dustIrrigation water

What is soil biology

http://www.chromographicsinstitute.com/2013/02/some-notes-about-soil-frdr-elaine-ingram/

Surface residues important

Roots important

Fueling soil biological activity

What do soil organisms need?

Suitable habitat Something to hold onto Water Oxygen Balanced pH

Carbon sources to consumeAccess to nutrients

Fractions of soil organic carbon

Total Organic C

Particulate Organic C

SMBC

CMIN PlantResidue C

} Active

} Slow

} Resistant

Soil microbial activity biologically sequesters N into

organic matter

Nitrogen and carbon mineralization have a complex relationship in the short-term…

Soil Organic Carbon Accumulation (lb C / acre / year)0 250 500 750 1000

Soil OrganicNitrogen

Accumulation(lb N / acre / year)

0

25

50

75

100

Hayed bermudagrassHayed bermudagrass

Unharvested grass (CRP)

Hayed bermudagrass


Grazed lightly to moderately

Hayed bermudagrass


Grazed lightly to moderately

Soil organic C and N are closely associated in the long- term

Franzluebbers and Stuedemann (2010) Soil Sci. Soc. Am. J. 74:2131-2141

Franzluebbers et al. (1995) Soil Sci. Soc. Am. J. 59:1618-1624

…most farm fields will be in some steady-state condition due to family-farm management

Thus, balancing the short- and long-term effects

Soil process relationships

Franzluebbers et al. (1999) Soil Sci. Soc. Am. J. 64:613-623

Days of Incubation0 7 14 21 28

CumulativeCarbon

Mineralization(mg . kg-1 soil)

0

100

200

300

400

5000-10-cm depth

10-20-cm depth

20-30-cm depth

The flush of CO2 following rewetting of dried soil

…reveals the soil’s underlying biological and sustainable yield

…possible to reduce nutrient inputs and improve yield sustainability

Preliminary results – all sites

Variable WatkinsvilleGA

ColumbiaMO

MandanND

ScottsbluffNE

BrookingsSD

Flush of CO2 75 21 58 13 5

CMIN0-24 d 95 6 108 9 9

SMBC 43 6 14 7 2

POXC 14 10 18 6 5

Protein 1 1 9 1 0

Treatment F value

Variable WatkinsvilleGA

ColumbiaMO

MandanND

ScottsbluffNE

BrookingsSD

Flush of CO2 10 11 14 16 10

CMIN0-24 d 8 19 10 19 10

SMBC 15 25 21 25 22

POXC 17 11 9 18 11

Protein 59 69 23 87 50

Coefficient of variation (CV, %)

Days of Incubation0 7 14 21 28

CumulativeCarbon

Mineralization(mg . kg-1 soil)

0

100

200

300

400

5000-10-cm depth

10-20-cm depth

20-30-cm depth

Some key considerations

Representative sample of field of influence

Defined soil depth

Oven-dried sample (55 °C, 3 d)

Sieved coarsely to <4.75 mm

Rewetted to 50% WFPS

Accurate determination of CO2 – alkali trap / titration

The flush of CO2 following rewetting of dried soil

Data from Franzluebbers et al. (2007) Soil Till. Res. 96:303-315

The flush of CO2 is an indicator of soil microbial activity

Flush of CO2 following Rewetting of Dried Soil(mg CO2-C

. kg-1 soil)0-3 d

0 100 200 300 400 500 600

BasalSoil

Respiration(mg CO2-C

. kg-1 soil . d-1)

0

10

20

30

40

50BSR = -2.3 + 0.07 * Flushr2 = 0.96

Data from Jangid et al. (2008, 2010, 2011) Soil Biol. Biochem. 40:2843-2853; 42:302-312; 43:2184-2193

The flush of CO2 relates well to soil microbial biomass C


. kg-1 soil)0-3 d

0 100 200 300 400 500

SoilMicrobial

Biomass C(mg . kg-1 soil)

0

300

600

900

1200

1500SMBC = 162 + 2.45 * Flushr2 = 0.76

Georgia

Kansas

Michigan


. kg-1 soil)0-3 d

0 200 400 600 800

Net NitrogenMineralization(mg . kg-1)0-24 d

0

50

100

150

200

>30% clay contentNMIN = 2.2 + 0.245*Flushr2=0.79, n=116


20-30% clay contentNMIN = 1.8 + 0.275*Flushr2=0.83, n=172>30% clay contentNMIN = 2.2 + 0.245*Flushr2=0.79, n=116

20-30% clay contentNMIN = 1.8 + 0.275*Flushr2=0.83, n=172

<20% clay contentNMIN = 5.6 + 0.237*Flushr2=0.63, n=123


20-30% clay contentNMIN = 1.8 + 0.275*Flushr2=0.83, n=172

<20% clay contentNMIN = 5.6 + 0.237*Flushr2=0.63, n=123

Across all soil texturesNMIN = 2.4 + 0.263*Flushr2=0.80, n=411

Data from M.R. Pershing (2016) NC State thesis

From multiple locations and depths within 61 different fields throughout North Carolina

The flush of CO2 shows association with N availability


RelativeYield

(fraction)

0.0

0.2

0.4

0.6

0.8

1.0

Goal of enlarging the biologically active N pool without causing

N leakage

Inorganic nitrogen Surface soil Residual in profile

Organic nitrogen Long-term stable Biologically active

Accounting for

Available Nitrogen (kg N ha-1)

Idealized response to nitrogen

Sites with low N availability and high N fertilizer response

Farm profit

Sites with high N availability and low N

fertilizer response

Environmental impact

Not all fields have the same available N


RelativeYield

(fraction)

0.0

0.2

0.4

0.6

0.8

1.0

Inorganic nitrogen Surface soil Residual in profile

Organic nitrogen Long-term stable Biologically active

Accounting for

Consider this evidence…Plant N uptake in semi-controlled greenhouse experiments

Plant dry matter production in minor relationship with total organic C

Pershing (2016) NC State University MS thesis

Soil from 30 sites in NC + VA(0-10, 10-20, 20-30 cm depths each)

Total Organic Carbon(g C . kg-1 soil)

0 10 20 30 40 50 60 70

PlantDry MatterProduction

(mg DM . g-1 soil)

0

2

4

6

8

DM = 2.2 + 0.041 (TOC)r2 = 0.22

Plant dry matter production with no relationship to humic matter

Humic Matter(g . 100 g-1 soil)

0 2 4 6 8 10


(mg DM . g-1 soil)

0

2

4

6

8DM = 2.9 + 0.006 (HM)r2 = 0.00

from NCDA labPershing (2016) NC State University MS thesis


Plant dry matter production in moderate relationship with residual inorganic N

Residual Inorganic Nitrogen(mg NH4-N + NO3-N

. kg-1 soil)

0 20 40 60 80 100


(mg DM . g-1 soil)

0

2

4

6

8

DM = 2.2 + 0.060 (RIN)r2 = 0.33



Plant dry matter production in strong relationship with net N mineralization

Net N Mineralization(mg N . kg-1 soil)0-24 d

0 40 80 120 160


(mg DM . g-1 soil)

0

2

4

6

8

DM = 1.6 + 0.031 (NMIN)r2 = 0.76



Plant N uptake in strong relationship with plant available N

Plant Available Nitrogen(residual inorganic + mineralizable)

(mg N . kg-1 soil)0-24 d

0 50 100 150 200

PlantNitrogenUptake

(mg N . kg-1 soil)

0

50

100

150

200PNU = 6.2 + 0.55 (PAN)r2 = 0.89



The flush of CO2 in strong relationship with plant available N

Plant Available Nitrogen(residual inorganic + mineralizable)

(mg N . kg-1 soil)0-24 d

0 40 80 120 160 200

Flushof CO2

FollowingRewetting

of Dried Soil(mg C . kg-1 soil)0-3 d

0

200

400

600

800Flush CO2 = -23 + 3.2 (PAN)r2 = 0.88



Plant N uptake in strong relationship with the flushof CO2

Flush of CO2 Following Rewetting of Dried Soil(mg CO2-C

. kg-1 soil)0-3 d

0 200 400 600 800

PlantNitrogenUptake

(mg N . kg-1 soil)

0

50

100

150

200PNU = 12 + 0.16 (Flush)r2 = 0.88



Field calibration to N requirements

Example of 3 strips fertilized with 0, 69, and 125 kg N ha-1 at sidedress

- Corn grain and silage in North Carolina and Virginia

Location of corn N trials

1 2 3 4

Soil sampling- 8 cores from each of 4 replicate locations

Soil analysesFlush of CO2, net nitrogen mineralizationRoutine soil testing for pH, P, K, other elements (NC Dept Agric)Bulk density, particle size, total C-N, microbial biomass C, inorganic N

Rep 4Rep 3Rep 2Rep 1

1140’

84

0’

Rockingham Co VA – 2016MD

North field(conventional)

South field(biological)

32-row strips of each sidedress N rate

0 N

140 N

70 N

0 N

70 N

140 N

Cost-return scenarios

Condition

Thresholdreturn

needed(lb grain/lb N)

Low N ($0.50/lb N) and high grain ($5.60/bu) 5

Low N ($0.50/lb N) and low grain ($2.80/bu) 10High N ($1.00/lb N) and high grain ($5.60/bu) 10

High N ($1.00/lb N) and low grain ($2.80/bu) 20

Nitrogen Rate (lb N/a)(at sidedress)

0 50 100 150

CornGrainYield(bu/a)

125

150

175

200

Rep 1

Rockingham Co VA – 2016MD North field (conventional)

Optimum N(lb N/a)

ThresholdL M H5 10 20

140 140 108

Rep 2

140 140 0

Rep 3

140 140 0

Rep 4

140 140 112

Average

Rockingham Co VA – 2016MD South field (biologicals)

Optimum N(lb N/a)

ThresholdL M H5 10 20

Nitrogen Rate (lb N/a)(at sidedress)

0 50 100 150

CornGrainYield(bu/a)

150

175

200

225

250

Rep 1

140 140 0

Rep 2

140 140 0

Rep 3

140 140 0

Rep 4

69 53 36

Average

140 122 28

Yield data from across farms in NC and VA

Total of 36 fields in NC + VA

Flush of CO2 (mg CO2-C . kg-1 soil)0-3 d

0 200 400 600 800

RelativeCorn Grain Yield

withoutSidedress N

(fraction)

0.0

0.2

0.4

0.6

0.8

1.0

r2 = 0.64n = 32

Total of 32 grain fields in NC + VA and 11 silage fields in VA

Similarity in yield response between both grain and silage


0 200 400 600 800

RelativeCorn Yield

withoutSidedress N

(fraction)

0.0

0.2

0.4

0.6

0.8

1.0

r2 = 0.64n = 43


0 200 400 600 800

Sidedress NitrogenRequired to Achieve

Optimum Corn Grain Yield(lb N/bu grain)

0.0

0.2

0.4

0.6

0.8

1.0 NR = 1.05 - 0.0015 * Flushr2 = 0.29

n = 36

Adjustment of N per bushel of grain…

Total of 36 fields in NC + VA


0 200 400 600 800


Optimum Corn Silage Yield(lb N/ton silage)

0

2

4

6

8

10N = 7.2 - 0.014 * Flush

r2 = 0.44n = 11

Total of 11 fields in VA

Adjustment of N per ton of silage…

Preliminary analysis for recommendation domain

Soil-Test Biological Activity

Very Low

LowMedium

HighFlush of CO2 (mg CO2-C

. kg-1 soil)0-3 d

0 200 400 600 800


Optimum Corn Grain Yield(lb N/bu grain)

0.0

0.2

0.4

0.6

0.8

1.0 NR = 1.05 - 0.0015 * Flushr2 = 0.29

n = 36

Very High

Wheat grain evaluations in North Carolina- 5 sites in 2015, 4 sites in 2016, and 10 sites in 2017

Location of wheat N trials

Flush of CO2 following Rewetting of Dried Soil(mg CO2-C kg-1 soil)0-3 days

0 200 400 600 800

Relative WheatDry Matter Yield

withoutN fertilizer

compared with135 kg N ha-1

(fraction)

0.0

0.2

0.4

0.6

0.8

1.0

Relative Yield = 1.14 * e-0.0048 * Flush

r2 = 0.48

Wheat yield response in NC

Total of 9 fields in western NC

Autumn stockpiling of tall fescue- 19 sites in 2015 and 35 sites in 2016

Location oftall fescue N trials


. kg-1 soil)0-3 d

0 200 400 600 800

Net NitrogenMineralization

(mg . kg-1 soil)0-24 d

0

50

100

150

200

250NMIN = -23 + 0.40 * Flushr2 = 0.77


. kg-1 soil)0-3 d

0 200 400 600 800

Net NitrogenMineralization

(mg . kg-1 soil)0-24 d

0

50

100

150

200

250NMIN = -23 + 0.40 * Flushr2 = 0.77

Tall fescue nitrogen trials

Pehim-Limbu et al. (unpublished data)

Asssssssss ss ssssssss ssssssssssss ss ssss ssssssssss


Nitrogen Fertilizer Rate (kg N . ha-1)0 50 100 150

ForageDry Matter

Yield@ 15% moisture

(kg . ha-1)

0

1000

2000

3000

An example from site near Butner NC


Cost-return scenarios

Condition

Thresholdreturn

needed(lb forage/lb N)

Low N ($0.50/lb N) and high hay ($200/ton) 5

Low N ($0.50/lb N) and low hay ($100/ton) 10High N ($1.00/lb N) and high hay ($200/ton) 10

High N ($1.00/lb N) and low hay ($100/ton) 20

Soil-Test Biological Activity(mg CO2-C

. kg-1 soil)0-3 d

0 200 400 600 800

Tall FescueYield Response

to Initial Dose of N(kg DM . kg-1 N)

0

10

20

30

r2 = 0.80



Soil-Test Biological Activity(mg CO2-C

. kg-1 soil)0-3 d

0 200 400 600 800

Tall FescueYield Response

to Initial Dose of N(kg DM . kg-1 N)

0

10

20

30

40Composite analysis of 19 sites in 2015/16

Mean + standard deviation at each siteStrenth of fit of means (r2 = 0.80)

Coefficient of variationFlush of CO2 = 12 + 8%Yield response = 106 + 44%




. kg-1 soil)0-3 d

0 200 400 600 800

Nitrogen Rateto Achieve

Optimum Yield(kg N . ha-1)

0

30

60

90

120

150

NR = 10 + 502 * e(-0.0159 * Flush)

r2 = 0.26, n = 80



Soil-test biological activity

(mg CO2-C kg-1 soil 3 d-1)

Nitrogen fertilizer to achieve optimum yield

(lb N/a)

<200 55 + 45200-400 8 + 18

>400 13 + 30


RelativeYield

(fraction)

0.0

0.2

0.4

0.6

0.8

1.0Sites with high N

availability and low N fertilizer response

Goal of enlarging the biologically active N pool without causing

N leakage

Flush of CO2 (mg . kg-1 soil)0-3 d

Sites with low N availability and high N fertilizer response

The flush of CO2 as a predictive soil test

Farm profit

Environmental impact

A working hypothesis…

Incubating soil in sealed jar with alkali to absorb CO2

Components

o 1-L canning jar with lid

o Two 60-mL graduated bottles with 50 g soil wetted to 50% WFPS (***)

o One 30-mL screw-cap vial containing 10 mL of 1 M NaOH to absorb CO2

o One 25-mL vial containing 10 mL water to maintain humidity

*** One bottle pre-incubated for 10 days prior to CHCl3

fumigation to estimate soil microbial biomass C

One bottle incubated for 24 days to determine cumulative C and N mineralization

Soil biological activity is a key indicator for productivity and environmental quality

The flush of CO2 possesses many qualities of a robust soil test Rapid Inexpensive Reproducible Suitable for a wide range of soils Correlating to nutrient needs of crops

assessing soil biological activity as an indicator of …sarc.calpoly.edu/pdfs/events/2017 field...

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