Integrating Nitrogen andIntegrating Nitrogen and Phosphorus with Carbon Cycling in SWATCycling in SWAT

Armen R. Kemanian, Texas AgriLife Research, Temple TXgStefan Julich, Justus-Liebig University, Giessen, GermanyJeffrey G. Arnold, USDA-ARS, Temple TX

2009 SWAT ConferenceJuly 8, 2009 Boulder, CO

Improving Life through Science and Technology

Outline

• Carbon cycling modeling relevanceB i f hi t i l b k d• Brief historical background

• Challenges• Sub-module description• Sub-module description• Sample simulations• Concluding remarksg

Photo courtesy of Hyrum Johnson

Carbon cycling modeling relevance

• Key component of soil productivity and environmental integrityenvironmental integrity

• C, N, and P cycling closely linked• Dissolved C role in pollutants transport and in-

tstream processes• Soil C storage role in regulating atmospheric CO2

concentration• Biomass harvest and the soil C balance

More than a century of research

• Hénin and Dupuis (1945): carbon balanceJ (1958) t i t• Jansson (1958): tracer experiments

• Swift (1979): the decomposition cascade• Jenkinson and Rayner (1977): multiple carbon• Jenkinson and Rayner (1977): multiple carbon

pools, Roth-C model• Paul & coworkers (1979 - present)• Phoenix model (McGill et al. 1981)• Century, NCSoil, Verberne et al. (1980-90)• Hassink & Withmore (1997): Saturation• SOC composition revisited (2000 ….)

What is soil organic matter?

A continuous of products from decaying organisms, and their exudates and excreta sometimes charredand their exudates and excreta, sometimes charred

Concept of SOM as polymeric macromolecular structures transitioned to non-covalent association ofstructures transitioned to non covalent association of low-molecular-mass, recognizable biomolecules in various stages of decomposition (Hedges et al., 2000; Burdon, 2001; Wrobel et al., 2003; Sutton and Piccolo, 2001; Smejkalova and Piccolo, 2008)

Most processes directly affecting SOM formation p y goccur at nanometer- and millimeter-scales, at specific locations in the soil matrix

Modeling – the balance equation

dCs/dt = hCi – kCs

Rate of Change = Inputs – Outputs

Inputs: vegetation residues, …

Outputs: erosion, microbes respiration, …

Modeling – the balance equation

dCs/dt = hCi – kCs

0.12

0.16

nc

SOIL A

SOIL B

Soil organic carbon is composed of

0.00

0.04

0.08

Freq

uencomposed of

fractions with varying turnover

t 0.001 10 100 1000 10000

Turnover Time (year)

rates

SWAT sub-model approach

• Soil organic matter composed of one pool with variable properties:pool, with variable properties:–variable C:N ratio

variable C:P ratio–variable C:P ratio–variable turnover rate

• Residues humification controlled by soil organic carbon content (saturation g (content)

SWAT carbon sub-model approach

Litter Litter

Ci

ManureRootsPOM*

NiNO3

ManureRootsPOM*

i

CO2

Cs

iNH4

Ns

humificationdecomposition

Microbial biomassHumus

Microbial biomassHumus

mineralization -immobilization

•Cs and texture control the humification

•Cs, tillage, texture,

•Residues C:N and mineral N control the C:N ratio of the newly formed SOMCs, tillage, texture,

temperature, moisture, control the decomposition

y

Core soil carbon balance equation

Change Carbon Storage = Inputs – Outputs

dCs/dt = hCi – kCs

h = hc[1 – (Cs/Cx)n]k = f ftk (C /C )mk feftkx(Cs/Cx)

hc depends on soil textureCx depends on soil texture (Hassink and Withmore, 1997)fe soil temperature and water content factorf f ti f till t l d b f ti (NRCS)ft function of tillage tool and number of operations (NRCS)

Controls: Tillage

1 0tThe effect of tillage and SOM

decomposition rate

0.4

0.6

0.8

1.0

enha

ncem

ent

On each layer, tillage accelerates decomposition; soil settling returns this variable to zero

0.0

0.2

0 1 2 3

Dec

omp

Cumulative mixing efficiencyCumulative mixing efficiency

The tillage enhancement effect12

15

men

t

Texture effect on tillage

The tillage enhancement effect depends on the layer texture

3

6

9

12

Max

enh

ance

m

0

3

0.0 0.2 0.4 0.6

M

Fractional clay content

Controls: residue C:N ratio

Residue C:N ratio and N The lower the C:N ratio of the residue, and the higher the mineral nitrogen concentration, th l th C N ti f th

13

15

:N ra

tio

mineral on C:N ratio of SOM 1 ppm N4 ppm N32 ppm N the lower the C:N ratio of the

newly formed SOM

7

9

11

SOM

C

32 ppm N

0 50 100 150 200Residue C:N ratio

Testing: Pendleton OR (1931)

Climate: semi-arid, winter precipitation

S il W ll W ll ilt lSoils: Walla Walla silt loam

Original vegetation: shrub / sagebrush –grassland

R t ti i t h t / f llRotation: winter wheat / summer fallow

Tillage: moldboard plow in fall + operations to control weeds during p gsummer

Source: Rasmussen and Smiley, 1996 and others

Testing: Pendleton OR

Treatment: 0 kg N ha-1

50

60

a

Sim top 30 cm Sim 30 to 60 cmObs top 30 cm Obs 30 to 60 cm

Obs Sim Diff

Yield, Mg ha-1 2.6 3.2 +0.6

Stover, Mg ha-1 4.5 4.5 +0.030

40

50

SOC

Mg/

ha

S o e , g a 5 5 0 020

1920 1940 1960 1980 2000Year

60

40

50

60

C M

g/ha

Treatment: 45 / 90 kg N ha-1

Obs Sim Diff

Yield, Mg ha-1 3.7 4.2 +0.5

20

30

1920 1940 1960 1980 2000SO

Yield, Mg ha 3.7 4.2 0.5

Stover, Mg ha-1 4.9 4.8 -0.1

Year

Testing: Pendleton OR

Manure 110 kg N ha-1 + 1.5 Mg C ha-1

50

60

a

Obs Sim Diff

Yield, Mg ha-1 4.2 4.4 +0.2 30

40

50

SOC

Mg/

ha

Stover, Mg ha-1 7.0 6.1 -0.9 201920 1940 1960 1980 2000

Year

40

50

60

C M

g/ha

Treatment: 45 / 90 kg N ha-1, starting on 1894

comment on top layercomment on sub-soilsame difficulties expected in N-based

20

30

1880 1900 1920 1940 1960 1980 2000SO

same difficulties expected in N based models

Year

Testing: Pendleton OR

Winter SummerSpring Winter SummerSpring WinterFallFall

6ac

tor

Wheat WheatMechanical Fallow

2

4

Tilla

ge F

a

0 - 10 cm10 - 20 cm

T = tillage event

0

2

1 101 201 301 401 501 601 701

T 10 20 cm20 - 30 cm

TT T T T

1 101 201 301 401 501 601 701

Day Count Progression

Testing: Pendleton OR

Testing: College Station, TX

Climate: subtropical, hot and humid summer: 940 mm / year, 20 C MATsummer: 940 mm / year, 20 C MAT

Soils: Weswood

Original vegetation: grassland, woodland

R t ti h t ltRotation: wheat monoculture

Tillage: three to four operations per yearSource: Dou et al 2007 Soil Science 172 124-131Source: Dou et al., 2007. Soil Science 172, 124 131

Testing: College Station, TX

12

14

16kg

-1so

il0 - 5 cm 5 15 cm

NT in 2002: 15.0 g kg-1

CT i 2002 11 1 k 1

8

10

bon,

g C

k 5 - 15 cm15 - 30 cm30 - 55 cm55 - 80 cm

CT in 2002: 11.1 g kg-1

NT = CT in 2002: 0.83 g kg-1

2

4

6

gani

c C

arb

80 - 105 cm

00 50 100 150 200

Org

Yearea

Testing: Central Texas Vertisols

Climate: subtropical, dry summer

P i it ti 750 900 /Precipitation 750 - 900 mm / year

Temperature 18 - 20 C MAT

Original vegetation: tallgrass prairieOriginal vegetation: tallgrass prairie

R t ti i l t d tiRotation simulated: continuous corn

Tillage: three to four operations per yearSource of SOC data: Potter et al 1999Source of SOC data: Potter et al., 1999

Testing: Central Texas Vertisols

0 0 0 5 1 0 1 5 2 0Organic Carbon, g C kg-1 soil

0.0

0.2

0.0 0.5 1.0 1.5 2.0

simulation year 1

0.4

0.6pth,

m

simulation year 25simulation year 50TempleBurleson

0.8

1.0

Dep Riesel

1.2

Concluding Remarks

AdvancesAdvances

• Integration of N, P, and C in SWAT

• The effect of tillage on several processes can be now simulated

Notes of caution

C• Carbon cycling below the plow layer is not clearly understood

• Uncertainties in all components of the C (or N) balance p ( )make accurate predictions of C accumulation rate difficult

• Forest soils and organic horizons not tested yetForest soils and organic horizons not tested yet

Acknowledgements

IndividualsNancy SammonsNancy SammonsShawn Quisenberry

InstitutionsTexas AgriLife ResearchUSDA-ARSJustus-Liebig University

Questions