assessing soil biological activity as an indicator of …sarc.calpoly.edu/pdfs/events/2017 field...
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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
Unharvested grass (CRP)
Grazed lightly to moderately
Hayed bermudagrass
Unharvested grass (CRP)
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
Flush of CO2 following Rewetting of Dried Soil(mg CO2-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
Flush of CO2 following Rewetting of Dried Soil(mg CO2-C
. 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
>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
>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
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
Available Nitrogen (kg ha-1)
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
Available Nitrogen (kg ha-1)
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
PlantDry MatterProduction
(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
Soil from 30 sites in NC + VA(0-10, 10-20, 20-30 cm depths each)
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
PlantDry MatterProduction
(mg DM . g-1 soil)
0
2
4
6
8
DM = 2.2 + 0.060 (RIN)r2 = 0.33
Pershing (2016) NC State University MS thesis
Soil from 30 sites in NC + VA(0-10, 10-20, 20-30 cm depths each)
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
PlantDry MatterProduction
(mg DM . g-1 soil)
0
2
4
6
8
DM = 1.6 + 0.031 (NMIN)r2 = 0.76
Pershing (2016) NC State University MS thesis
Soil from 30 sites in NC + VA(0-10, 10-20, 20-30 cm depths each)
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
Pershing (2016) NC State University MS thesis
Soil from 30 sites in NC + VA(0-10, 10-20, 20-30 cm depths each)
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
Pershing (2016) NC State University MS thesis
Soil from 30 sites in NC + VA(0-10, 10-20, 20-30 cm depths each)
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
Pershing (2016) NC State University MS thesis
Soil from 30 sites in NC + VA(0-10, 10-20, 20-30 cm depths each)
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
Flush of CO2 (mg CO2-C . kg-1 soil)0-3 d
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
Flush of CO2 (mg CO2-C . kg-1 soil)0-3 d
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
Flush of CO2 (mg CO2-C . kg-1 soil)0-3 d
0 200 400 600 800
Sidedress NitrogenRequired to Achieve
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
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
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
Flush of CO2 following Rewetting of Dried Soil(mg CO2-C
. 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
Flush of CO2 following Rewetting of Dried Soil(mg CO2-C
. 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
Pehim-Limbu et al. (unpublished data)
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
Tall fescue nitrogen trials
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
Tall fescue nitrogen trials
Pehim-Limbu et al. (unpublished data)
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%
Tall fescue nitrogen trials
Pehim-Limbu et al. (unpublished data)
Flush of CO2 following Rewetting of Dried Soil(mg CO2-C
. 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
Tall fescue nitrogen trials
Tall fescue nitrogen trials
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
Available Nitrogen (kg ha-1)
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