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Effects of Landscape Position and Temperate Alley Cropping Practices on Soil Carbon Dioxide and Nitrous Oxide Flux in an

This study assesses the effects of vegetative conservation practices and landscape position on soil carbon and nitrogen distribution, as well as N2O and CO2 efflux in an agricultural watershed in northeast Missouri.

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Effects of Landscape Position and Temperate Alley Cropping Practices on Soil Carbon Dioxide and Nitrous Oxide Flux in an

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  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. MATERIALS AND METHODS Watershed Field Study:

  8. 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.

  9. 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.

  10. 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

  11. Landscape TOC POM C DOC position GR AF CR GR AF CR GR AF CR--------------------------- g kg-1 soil -------------------------- -------- mg kg-1 soil ------ Upper 19.5 24.5 19.5 3.54 6.60 3.03 106.8 123.3 80.1 Middle 22.5 23.5 22.0 5.42 5.76 4.52 105.7 147.2 75.0 Lower 25.5 24.0 18.5 7.12 7.38 3.28 133.5 124.6 72.4 LSD(0.10) ------------- 2.4 ------------ ----------- 2.68 ------------ ------------ 22.2 ------------ SOIL C DISTRIBUTION

  12. Lower backslope FIELD STUDY: NITROUS OXIDE FLUX N2O flux rates generally were higher than what has been found by others Upper backslope

  13. 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

  14. Lower backslope Upper backslope Above 60 to 80% WFPS is conducive to high rates of N2O production FIELD STUDY: SOIL WATER-FILLED PORE SPACE 2003 Precip. = 93 cm Long-term average = 92 cm

  15. LAB: EFFECTS OF WFPS ON N2O EVOLVED 60 With Added N 45 AF Cumulative N2O evolved (mg N2O-N kg soil-1) CR 30 GR 15 0 40 60 80 100 % WFPS

  16. Lower backslope Upper backslope FIELD STUDY: CO2 FLUX Soil CO2 flux rates included both root and microbial respiration

  17. Management effects FIELD STUDY: CUMULATIVE CO2 PRODUCED Landscape position effects

  18. AF CR GR LAB: EFFECTS OF WFPS ON CO2 EVOLVED With Added N

  19. 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

  20. 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

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