Neal Bailey, Peter Motavalli*,

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EFFECTS OF LANDSCAPE POSITION AND TEMPERATE ALLEY
CROPPING PRACTICES ON SOIL CARBON DIOXIDE AND
NITROUS OXIDE FLUX IN AN AGRICULTURAL WATERSHED
Neal Bailey, Peter Motavalli, Ranjith Udawatta
and Kelly Nelson, University of Missouri
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INTRODUCTION

• Increasing concern over the contribution of
  agriculture to global warming through production
  of greenhouse gases (e.g. CO2, N2O and CH4).
• Agroforestry practices, such as alley cropping,
  have been estimated to sequester up to 73.8 Tg
  C/year (Montagnini and Nair, 2004).
• Factors influencing greenhouse gas emissions from
  soils in agricultural watersheds include C and N
  sources (e.g. N fertilizer and crop residues) and
  sinks (e.g. vegetation, SOM), soil water content,
  soil temperature, and soil runoff and erosion
  losses.

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INTRODUCTION (CONTINUED)

• The presence of claypan soils, a restrictive
  subsoil layer, at varying depths across
  landscapes in northeast Missouri may influence
  CO2 and N2O production since this soil often
  causes relatively higher soil water content in
  the overlying horizon and greater runoff.

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INTRODUCTION (CONTINUED)

• Vegetative contour strips may affect CO2 and N2O
  production since they can reduce runoff and
  nutrient loss and increase water infiltration.
  They may also affect soil biological activity due
  to changes in microclimate within or close to the
  contour strip.

• Little information available regarding the
  effects of landscape position and management
  systems, such as agroforestry, on distribution of
  soil carbon (C) and nitrogen (N) and greenhouse
  gas flux.

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OBJECTIVE

• To assess the effects of vegetative conservation
  practices (i.e. alley cropping and grass contour
  strips) and landscape position on soil C and N
  distribution and N2O and CO2 efflux in three
  adjacent agricultural watersheds with claypan
  soils in northeast Missouri.

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MATERIALS AND METHODS

• Field study with three adjacent watersheds in
  northeast Missouri cropped to a no-till
  corn-soybean rotation from 1991 to 1996. In
  1997, each watershed was randomly assigned
  treatments of? Cropped-only (CR) with an area
  of 1.65 ha.? Cropped with grass contour
  strips (GS) with an area of 3.16 ha.? Alley
  cropping system of row crops with grass- tree
  contour strips (AF) with an area of 4.44 ha.

Trees Pin oak, swamp white oak and
burr oak Grasses redtop grass, brome grass,
and birdsfoot trefoil
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MATERIALS AND METHODS
Watershed Field Study
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MATERIALS AND METHODS

• Landscape positions within each watershed were
  designated as upper backslope (UBS), middle
  backslope (MBS) and lower backslope (LBS).
• Soil samples were collected from two sampling
  transects in each watershed in fall, 2003 at each
  landscape position from the 0 to 10 cm depth for
  analysis of soil bulk density, total organic C,
  total N, particulate organic matter C and N and
  dissolved organic C and N.

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MATERIALS AND METHODS

• Gas flux sampling occurred from April to
  October, 2004 before and after N fertilizer
  application.
• Surface soil CO2 efflux was measured in the field
  by using a portable infrared CO2 analyzer fitted
  with a closed chamber.

• Surface soil N2O efflux was measured with a Buck
  Scientific Model 910 gas chromatograph equipped
  with an electron capture detector (ECD) after
  samples were collected in vacuum storage bottles
  and transported from the field.
• Soil water content and temperature were
  determined at the 0 to 5 cm depth at each CO2 and
  N2O efflux measurement.

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MATERIALS AND METHODS LABORATORY STUDY

• Bulk soils were collected in Nov. 2003 to a depth
  of 10 cm from the upper backslope position within
  the contour strips of the AF and GR watersheds
  and the corresponding position within the CR
  watershed
• A incubation at 25 C was conducted over 72 days
• Cores were periodically sampled for CO2 and N2O
  gas efflux
• Treatments for incubation
• Management soils (GR, CR, and AF)
• Water-filled pore space of 40, 60, 80, and 100
• Two N rates (0 and 0.6 g KNO3 core-1)
  approx. equivalent to the field application of
  180 kg N ha-1

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SOIL C DISTRIBUTION
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FIELD STUDY NITROUS OXIDE FLUX
Lower backslope
N2O flux rates generally were higher than what
has been found by others
Upper backslope
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Management effects
FIELD STUDY CUMULATIVE NITROUS OXIDE PRODUCED
The highest amount of N2O evolved under CR
management represented approx. 11 of the applied
N fertilizer
Landscape position effects
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FIELD STUDY SOIL WATER-FILLED PORE SPACE
2003 Precip. 93 cm Long-term average 92 cm
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LAB EFFECTS OF WFPS ON N2O EVOLVED
60
With Added N
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AF
Cumulative N2O evolved (mg N2O-N kg soil-1)
CR
30
GR
15
0
80
100
60
40
WFPS
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FIELD STUDY CO2 FLUX
Soil CO2 flux rates included both root and
microbial respiration
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Management effects
FIELD STUDY CUMULATIVE CO2 PRODUCED
Landscape position effects
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LAB EFFECTS OF WFPS ON CO2 EVOLVED
With Added N
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CONCLUSIONS

• Both landscape position and vegetative
  conservation practices affected distribution of
  soil C and N across agricultural watersheds with
  claypan soils.
• Permanent grass and agroforestry buffer strips
  generally had lower amounts of soil N2O
  production but higher cumulative CO2 production
  compared to the cropped areas.

A Missouri farm landscape
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CONCLUSIONS (CONTINUED)

• N2O and CO2 flux and cumulative release were
  generally higher than found in other research,
  possibly due to the effects of the restrictive
  claypan soil layer on soil water content and gas
  flux measurements.
• Additional research is needed to assess spatial
  variation in soil CO2 and N2O efflux by depth due
  to the differences in root distribution among
  vegetative components of the different management
  systems.

Alley cropping in Missouri