SOIL CO 2 AND N 2 O EMISSIONS FROM AN AGRICULTURAL WATERSHED AS INFLUENCED BY LANDSCAPE POSITION AND AGROFORESTRY CONSERVATION MANAGEMENT PRACTICES Neal J. Bailey Department of Soil, Environmental, and Atmospheric Sciences

Introduction Agroforestry is the practice of intentionally growing woody plants within a cropping system and is reputed for having economical and environmental benefits Agroforestry is the practice of intentionally growing woody plants within a cropping system and is reputed for having economical and environmental benefits The agroforestry system along with the grass contour strips were established in 1997 on the Greenley watershed site The agroforestry system along with the grass contour strips were established in 1997 on the Greenley watershed site

Greenley Paired Watershed GR AF CR

Vegetative filter strips increase nutrient retention and infiltration rates (Udawatta et al. 2002; Garrity 2004) Vegetative filter strips increase nutrient retention and infiltration rates (Udawatta et al. 2002; Garrity 2004) Agroforestry and grassland systems accumulate soil organic matter over time (Kaur et al. 2000; Corre et al. 1999) Agroforestry and grassland systems accumulate soil organic matter over time (Kaur et al. 2000; Corre et al. 1999) Carbon and nitrogen are major constituents of soil organic matter (Sharrow and Ismail 2004) Carbon and nitrogen are major constituents of soil organic matter (Sharrow and Ismail 2004) Introduction

Introduction Agroforestry and grass filter strips may contribute to the mitigation of the increased levels of atmospheric carbon dioxide (CO 2 ), and reduce the levels of nitrous oxide (N 2 O) production Agroforestry and grass filter strips may contribute to the mitigation of the increased levels of atmospheric carbon dioxide (CO 2 ), and reduce the levels of nitrous oxide (N 2 O) production Research regarding the effects of landscape position and temperate conservation management practices on the efflux of CO 2 and N 2 O in an agricultural watershed is limited Research regarding the effects of landscape position and temperate conservation management practices on the efflux of CO 2 and N 2 O in an agricultural watershed is limited

Introduction Atmospheric concentrations of CO 2 and N 2 O have increased considerably since 1750 Atmospheric concentrations of CO 2 and N 2 O have increased considerably since 1750 CO 2 has increased approximately 31% CO 2 has increased approximately 31%  From ca. 280 ppm to 360 ppm N 2 O has increased approximately 17% N 2 O has increased approximately 17%  From ca. 270 ppb to 315 ppb (IPCC, 2001)

Introduction All soils produce both CO 2 and N 2 O through the nutrient cycling process All soils produce both CO 2 and N 2 O through the nutrient cycling process However, the production rates can be exacerbated by agricultural practices However, the production rates can be exacerbated by agricultural practices  CO 2 – tillage and drainage  N 2 O – application of fertilizer N

Major sources of soil CO 2

Plant root respiration Plant root respiration  Corn field between percent of total soil respiration (Rochette et al. 1999)  Tall Grass Prairie and pasture grass 40 and 53 percent, respectively (Kucera and Kirkham, 1971; Robertson et al., 1995)  Oak forest 52 percent (Kelting et al., 1998)

Major Pathways of Soil N 2 O Formation NO 3 - NO 2 - NON2ON2ON2N2 Denitrification Nitrification NH 4 + NH 2 OH N2ON2O [HNO] NO NO 2 - NO 3 - NO 2 NHOH N2ON2O Linn and Doran (1984)

Objectives Determine the effects of landscape position and conservation management practices on: Determine the effects of landscape position and conservation management practices on:  Efflux rates of CO 2 and N 2 O  Distribution of total soil carbon and nitrogen Establish potential of soils collected in each watershed for production of CO 2 and N 2 O under controlled laboratory conditions Establish potential of soils collected in each watershed for production of CO 2 and N 2 O under controlled laboratory conditions

Materials and Methods- Field Paired watersheds, Greenley Research Station in northeast Missouri Paired watersheds, Greenley Research Station in northeast Missouri Management system in each watershed: Management system in each watershed:  Cropped-only (CR)  Cropped, interspersed with grass contour strips (GS)  Cropped, interspersed with grass-tree contour strips (AF) Landscape positions within each watershed were: summit, backslope, and footslope Landscape positions within each watershed were: summit, backslope, and footslope

Materials and Methods- Field Surface soil CO 2 efflux was measured in the field by using a portable infrared CO 2 analyzer fitted with a closed chamber Surface soil CO 2 efflux was measured in the field by using a portable infrared CO 2 analyzer fitted with a closed chamber N 2 O efflux was measured with a Buck Scientific Model 910 gas chromatograph equipped with an electron capture detector (ECD) after soil surface N 2 O samples were collected in vacuum storage bottles and transported from the field N 2 O efflux was measured with a Buck Scientific Model 910 gas chromatograph equipped with an electron capture detector (ECD) after soil surface N 2 O samples were collected in vacuum storage bottles and transported from the field

Gas flux sampling occurred from April to October, 2004 before and after N fertilizer application Gas flux sampling occurred from April to October, 2004 before and after N fertilizer application Soil water content and temperature were determined at the 0 to 5 cm depth at each CO 2 and N 2 O efflux measurement Soil water content and temperature were determined at the 0 to 5 cm depth at each CO 2 and N 2 O efflux measurement Materials and Methods- Field

The incubation was conducted for 43 days with packed cores at a bulk density of 1.2 g cm -3 The incubation was conducted for 43 days with packed cores at a bulk density of 1.2 g cm -3 Treatments for incubation: Treatments for incubation:  Management soils (GR, CR, and AF)  W ater-filled pore space of 40, 60, 80, and 100 percent  Nitrogen rate equivalent to the field application of 180 kg N ha -1 (0.6g KNO 3 - core -1 ) or 0g KNO 3 - core -1 Materials and Methods- Incubation

Total organic CTotal N Bulk density Landscape position GS AF C Landscape position GR AF CR GS AF C GR AF CR % % % Mg m Summit Backslope Footslope Distribution of Soil Properties- Field Total organic C Total N LSD (0.05) Two transects were sampled in November of 2003 in each watershed to determine D b, TN, and TC Two transects were sampled in November of 2003 in each watershed to determine D b, TN, and TC LSD (0.10)

% Water-Filled Pore Space- Field % WFPS DAA LSD (0.05) SummitBackslope Footslope NS %WFPS = (%w)(ρ b )/(1- ρ b /ρ s )

Surface CO 2 Flux - Field SummitBackslope Footslope Days after N application NS DNMRT (0.05) Grass-tree contour strip Cropped-only Grass contour strip Grass-tree contour strip Cropped-only Grass contour strip

Cumulative CO 2 - Field LSD (0.05) Estimated microbial contribution Accumulated CO 2 Management DAA CO 2 flux (µmol m -2 sec -1 ) kg CO 2 -C m NS LSD (0.10) Landscape position Accumulated CO 2 kg CO 2 -C m LSD (0.05)

Surface N 2 O Flux- Field Days after N application Grass-tree contour strip Cropped-only Grass contour strip Summit Backslope Footslope N 2 O efflux (g N 2 2 O O - - N ha day ) ) N 2 O efflux (g N 2 2 O O - - N ha day ) ) NS DNMRT (0.05)

NS Cumulative N 2 O- Field N 2 O flux (g N 2 O-N ha -1 day -1 ) DAA Management kg N 2 O-N ha Accumulated N 2 O LSD (0.05) Landscape position Accumulated N 2 O LSD (0.05)

CO 2 Flux- Incubation DAYDAY CO 2 efflux (mg CO 2 -C kg -1 soil Day -1 ) 80% WFPS 60% WFPS40% WFPS 100% WFPS LSD (0.05) CO 2 efflux (mg CO 2 -C kg -1 soil Day -1 )

N 2 O Flux- Incubation LSD (0.05) DAY N 2 O efflux (µgN 2 O-N kg soil -1 Day -1 ) DAY NS 80% WFPS 40% WFPS60% WFPS 100% WFPS

CO 2 and N 2 O Accumulated- Incubation CO 2 N2ON2O % WFPS LSD (0.05) mg N 2 O-N kg soil mg CO 2 -C kg soil

Both landscape position and management system affected soil CO 2 and N 2 O flux Both landscape position and management system affected soil CO 2 and N 2 O flux Possible factors affecting differences in flux were spatial and temporal variation in soil water- filled pore space, distribution of soil total organic C, total N, applied N fertilizer, and water extractable organic carbon Possible factors affecting differences in flux were spatial and temporal variation in soil water- filled pore space, distribution of soil total organic C, total N, applied N fertilizer, and water extractable organic carbon Improved understanding of these factors will assist in predicting and managing greenhouse gas flux in agricultural watersheds Improved understanding of these factors will assist in predicting and managing greenhouse gas flux in agricultural watersheds Conclusions

MU Center for Agroforestry MU Center for Agroforestry Dr. Peter Motavalli Dr. Peter Motavalli Dr. Robert Kremer, USDA-ARS Dr. Robert Kremer, USDA-ARS Greenley Research Center (Dr. Kelly Nelson, Randall Smoot and Matt Jones) Greenley Research Center (Dr. Kelly Nelson, Randall Smoot and Matt Jones) Dr. Ranjith Udawatta Dr. Ranjith Udawatta Dr. Mark Ellersieck Dr. Mark Ellersieck Eduardo Navarro Eduardo Navarro Dr. Stephen Anderson Dr. Stephen Anderson Dr. Randall Miles and Steve Troesser Dr. Randall Miles and Steve Troesser Acknowledgements