1. Compaction, Crop and Tillage Effects on Greenhouse Gases Emission From an Alfisol of Ohio David A.N. Ussiri and Rattan Lal Carbon Management and Sequestration Center, School of Environment and Natural Resources, The Ohio State University, 2021 Coffey Rd, Columbus, OH 43210. INTRODUCTION Anthropogenic activities are a major source of greenhouse gases (GHG) emission and agricultural activities contribute about 20% of GHG emissions. Carbon dioxide (CO 2 ), CH 4 and N 2 O are GHG mainly affected by agricultural activities. The main sources of CO 2 in aerobic soils are respiration and organic matter decomposition. About 10 to 30% of total anthropogenic emissions of CO 2 originate from agriculture and land use conversion (IPCC, 2001). Both natural and human sources emit CH 4 (IPCC, 2001). About 50% of current CH 4 emissions are anthropogenic (IPCC, 2001). Wetlands are natural sources of CH 4, while anthopogenic sources include agriculture, sewage, landfills and natural gas leakage. In agricultural soils, CH 4 is produced by methanogenesis bacteria under anaerobic conditions. The only known biological sink of atmospheric CH 4 is the oxidation in aerobic soils by methanotrophic bacteria (Hutsch, 2001). This sink can contribute up to 15% of the total CH 4 removal (Born et al., 1994). Therefore, soils can be net source or biological sinks for CH 4 depending on the land use and management practices. The objective of this study was to evaluate the effects of soil compaction, crop type and tillage management on CO 2, CH 4 and N 2 O emissions. MATERIALS AND METHODS The experiment was conducted at Western Branch Research Farm of the Ohio Agricultural Research and Development Center (OARDC; 39 o 45’N, 83 o 36’W). Soils are Crosby silt-loam (fine, mixed, mesic Aeric Ochraqualf) with 15, 65, and 20% sand, silt and clay, respectively (van Doren et al., 1976). Average annual temperature and precipitation are 10.8 o C and 1045 mm, respectively. CO 2 and CH 4 emission was monitored using the static chamber technique (Plate 1) comprising 15 cm diameter and 25 cm height gas chambers made of polyvinyl chloride (PVC) pipe (Jacinthe and Dick, 1997) and inserted 5 cm into the ground. Chambers remained in place for the entire sampling period except for temporary removal during farm operations. During sampling, chamber lid fitted with a sampling port was placed on semi-permanent PVC bases. CONCLUSIONS Fluxes of CO 2 were not affected by crop type, tillage or level of compaction, but were highly sensitive to air and soil temperature and water content. Fluxes of CH 4 increased with increase in precipitation and soil water content Compaction reduced the capability of agricultural soils to oxidize CH 4. REFERENCES Hutsch, B.W. 2001. Methane oxidation, nitrification, and counts of methanotrophic bacteria in soils from a long-term fertilization experiment. J. Plant Nutr. Sci. 164:21-28. IPCC. 2001. Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change Cambridge University Press, Cambridge, U.K. Jacinthe, P.A., and W.A. Dick. 1997. Soil management and nitrous oxide emissions from cultivated fields in southern Ohio. Soil Tillage Res. 41:221-235. RESULTS Daily CO 2 flux ranged from 0.7 to 4.8 g CO 2 -C m -2 d -1 (Fig. 2a, 3a). Highest rates of CO 2 emission were observed during June-July months which coincided with high soil temperatures and low soil moisture content (Fig. 1). Crop, tillage and compaction treatments had no significant effects on CO 2 fluxes (Table 2). CO 2 fluxes were positively correlated with air and soil temperatures but negatively correlated with gravimetric moisture content of soil and CH 4 fluxes (Table 1). Table 1. Relationship between CO 2 and CH 4 fluxes, temperature and soil moisture content ( * indicates significant at 5%) Air in the chamber headspace was sampled by a syringe (20 mL) at 0, 30 and 60 minutes intervals and transferred to crimp-sealed pre-evacuated (< 0.05 kPa) 10 mL vials fitted with rubber septa. All chambers were sampled on the same day. Air samples were analyzed by gas chromatograph fitted with thermal conductivity detector (TCD), flame ionization detector (FID) and electron capture detector (ECD) for CO 2, CH 4 and N 2 0 detections, respectively. At each sampling date, soil temperatures at 5, 10 and 20 cm depths were measured at the time of gas sampling using a digital soil thermocouple temperature probe for each plot. In addition, soil samples of the surface (0-10 cm depth) were collected for moisture content determination. Emission data were corrected for temperature and diffusion effects. Plate 1: Gas Chamber and lid CO 2 (g m -2 d -1 )CH 4 (mg m -2 d -1 ) Corn2.34 (0.40)2.33 (1.23) Oat2.50 (0.54)2.93 (1.36) Soybean2.14 (0.25)-1.15 (0.81) No Till2.27 (0.39)2.23 (0.75) Plow Till2.36 (0.41)0.96 (0.51) No compaction2.39 (0.55)-0.69 (0.32) Moderate compaction2.24 (0.42)2.18 (1.02) High compaction2.23 (0.28)3.25 (1.21) Table 2. Treatment effects on average daily CO 2 and CH 4 fluxes (standard errors in brackets). Precip.Air Temp.GMC Soil Temp. CH 4 CO 2 -0.260.66 * -0.52 * 0.64 * -0.46 * CH 4 0.81 * -0.390.92 * -0.65 * 1 Figure 2. Effects of crop type on CO 2 and CH 4 fluxes. Figure 1. Soil temperature (0-10 cm depth) and gravimetric moisture content during monitoring period. Figure 3. Effects of compaction on CO 2 and CH 4 fluxes Daily CH 4 flux ranged from -9.40 to 11.68 mg CH 4 -C m -2 d -1 (Fig. 2b, 3b). Highest emission rates were observed in March and early April. During this period, soil temperature were low, while GMC were high (Fig. 1; Table 1). On average, corn and oats plot emitted CH 4 (i.e. CH 4 source), while soybean plots oxidized CH 4 (i.e. CH 4 sink; Table 2). Daily CH 4 flux from plow tilled plot was significantly lower than fluxes from no till plots (Table 2), probably due to increased aeration, allowing greater diffusion which led to more CH 4 uptake. Level of compaction significantly influenced daily CH 4 fluxes. Overall, non compacted soils were sink while the compacted soils were sources of CH 4 (Table 2). Fluxes of CH 4 increased by nearly 50% when compaction increased from moderate (10 ton tractor) to high (20 ton tractor passage).