VEGETATIVE BARRIERS AND SOIL PROPERTIES

Humberto Blanco Assistant Professor in Applied Soil Physics

Agronomy & Horticulture University of Nebraska-Lincoln

John E. Gilley, Dean E. Eisenhauer, Paul J. Jasa, and Alan BoldtBiological Systems Engineering, University of Nebraska-Lincoln

Barriers are narrow strips of dense, tall and stiff-stemmed perennial grass planted across slope.

USDA Treynor-Watershed, IA(Larry A. Kramer, USDA-ARS, Deep Loess Research Station, Council Bluffs, IA)

What are Switchgrass Barriers?

BENEFITS OF SWITCHGRASS BARRIERS• Benefits of switchgrass barriers for reducing water erosion are well

known (Gilley et al., 2001; Dabney et al., 2012). Grass barriers: a. pond runoff and promote sediment deposition (Dabney et al., 1999)b. increase runoff water infiltration (Rachman et al., 2004)c. reduce pollutants in surface runoff (Gilley et al., 2000 and 2011).

USDA Treynor-Watershed, IA(Larry A. Kramer, USDA-ARS)

John Gilley, USDA-ARS)

Soil berms

Switchgrass

Ephemeral channel

Blanco-Canqui, H., C.J. Gantzer, S.H. Anderson, E.E. Alberts, and A.L. Thompson. 2004. Grass barrier and vegetative filter strip effectiveness in reducing runoff, sediment, nitrogen, and phosphorus loss. Soil Sci. Soc. Am. J. 68:1670-1678.

Our work in Missouri in 2001-2003 also showed that switchgrass barriers can reduce the transport of sediment and sediment-associated nutrients in runoff

Trough to collect runoff

WHAT ARE THE IMPACTS OF SWITCHGRASS BARRIERS ON SOIL PROPERTIES?

• Previous research on grass barriers has often focused on water erosion and water quality (Dabney et al., 1999; Gilley et al., 2000; Gilley et al. 2011; Dabney et al., 2012).

• Grass barriers may improve soil physical properties relative to row crops (Rachman et al., 2004).

• Grass barriers when integrated with row crops may also restore some of the soil C lost with intensive tillage.

• An improved understanding of the impacts of switchgrassbuffers on soil C and other soil properties is needed to manage and address emerging agricultural land use changes.

We quantified soil organic C pool, total N, particulate organic matter, and water-stable aggregates under switchgrass barriers and compared the results with cropped rows under conventional till and no-till conditions after 15 years of management in eastern NE.

SWITCHGRASS BARRIERS AND SOIL PROPERTIES: Rogers Memorial Farm (eastern NE)

Five narrow (1.4 m) switchgrass barriers under no-till and conventional till were established in 1998

Soil: Aksarben silty clay loam (fine, smectitic, mesic Typic Argiudoll). Slope: 5.4%.Rotation: grain sorghum-soybean-corn.

Location: University of Nebraska’s Rogers Memorial Farm located 18 km east of Lincoln, NE

UNL

SOIL SAMPLING: Nov, 2013Four sampling positions: • Switchgrass barrier• Deposition zone (0.5 m upslope

of the barrier)• Center of the cropped area (19

m between barriers). • Upper end of cropped area (1.4

m below the upslope barrier).

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Soil

dept

h (c

m)

Soil Organic C (g kg-1)

SwitchgrassBarrierCropped Area

LSD0.05

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0 10 20 30 40 50Soil Organic C (Mg ha-1)

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Soil

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Total Nitrogen (g kg-1)

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0 1 2 3 4 5Total Nitrogen (Mg ha-1)

LSD0.05

SWITCHGRASS BARRIERS AND SOIL ORGANIC C AND TOTAL N

Switchgrassbarriers accumulated about 0.85 Mg ha‐1 yr‐1 of soil C and 80 kg ha‐1 yr‐1of total N at the 0 to 15 cm depth. 

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Coarse POM (mg g-1)

SwitchgrassBarrierCroppedArea

LSD0.05

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0 2 4 6 8 10 12Fine POM (mg g-1)

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0 2 4 6 8 10 12Total POM (mg g-1)

SWITCHGRASS BARRIERS AND PARTICULATE ORGANIC MATTER

1.Data on SOC from switchgrass barrriers are few. 2.Near Treynor, IA, Rachman et al. (2004) found increased

SOC concentration under switchgrass hedges relative to row crops in the upper 30 cm depth.

3.After successful establishment, switchgrass barriers can have the potential to increase SOC concentration in sloping fields, eroded fields, or soils with initial low SOC levels.

SWITCHGRASS BARRIERS AND SOIL CARBON: OTHER STUDIES

SOIL AGGREGATE STABILITY AND POROSITY

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0.0 0.5 1.0 1.5 2.0 2.5 3.0

Soil

dept

h (c

m)

Mean Weight Diameter (mm)

Switchgrass Barrier

Cropped Area

LSD0.05

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40 43 46 49 52 55 58Total Porosity (%)

• Switchgrass barriers increased mean weight diameter of water-stable aggregates by 70% (0-15 cm) and by 40% (15-60 cm).

• Barriers also increased soil porosity by 4% to 9%.

y = 0.12x - 0.34r² = 0.79***

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Mea

n W

eigh

t Dia

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er o

f Agg

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(mm

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Soil Organic Carbon (g kg-1)

0 to 15 cm

y = 0.38x + 0.99r² = 0.36**

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0 1 2 3 4 5Coarse Particulate Organic Matter (g kg-1)

0 to 15 cm

y = 0.004x + 0.45r² = 0.22*

y = 0.006x + 0.39r² = 0.65***

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sity

Soil Organic Carbon (g kg-1)

0 to 15 cm15 to 30 cm

THE IMPACT OF SOIL ORGANIC MATTER ON SOIL PHYSICAL PROPERTIES

1. Inclusion of switchgrass barriers in conventionally tilled and no-till fields has the potential to increase soil C pool and improve soil structural properties.

2. Switchgrass barriers for storing SOC can be mainly confined to the upper 15 or 30 cm of soil profile.

3. Benefits for improving soil structural processes such as aggregation were measurable to a 60 cm depth.

4. Soil C was correlated with aggregation and porosity. 5. Switchgrass barriers can be an important component of

integrated agroecosystems for restoring soil C and improving soil properties.

TAKE AWAY MESSAGE

THANKS FOR YOUR ATTENTION