1. Fluxes of nitrous oxide and methane and soil carbon change in ten ecosystems along a management intensity gradient in SW Michigan Sara J. Parr, Andrew T. Corbin, and G. Philip Robertson Kellogg Biological Station and Department of Crop and Soil Sciences, Michigan State University Abstract Methods and Site Description Conclusions Acknowledgements Support for this research was provided in part by NSF (LTER), the CS Mott Foundation, The United Agribusiness League, the Michigan Women’s Farm and Garden Association, and the Michigan Agricultural Experiment Station. We would also like to thank Stacey VanderWulp, Sven Bohm, Terry Loecke, Tim Syswerda, Barb Fox, Joe Simmons, Greg Parker, Jane Boles, Stuart Grandy, and all the field crew for the LTER that contributed to this work. Gas fluxes and soil were collected from four annual cropping systems (corn- soybean-wheat rotations managed as conventional, no-till, low-input, and organic systems), two perennial systems (alfalfa and poplar trees), two successional systems (early and mid-successional old fields), and two forest systems (planted conifers and native deciduous systems). The treatments comprise the Long-Term Ecological Research (LTER) site at the W.K. Kellogg Biological Station (KBS) located in SW Michigan, replicated on Kalamazoo and Oshtemo soil series (Typic Hapludalfs). Management details appear in Table 1. Gas fluxes were sampled twice per month, except in winter, and analyzed for nitrous oxide, carbon dioxide, and methane. Soil for C analysis was collected in 2001 to one meter depth using a Geoprobe®, separated by profile horizon, and analyzed for carbon and nitrogen content. Further details on experimental design and agronomic protocols appear in Figures 1-2 and Tables 1-2, below, and at www.lter.kbs.msu.edu. Introduction Question 1: How does nitrous oxide flux vary across the management intensity gradient? Question 2: How does methane flux vary along the management intensity gradient? Fluxes of the greenhouse gases nitrous oxide and methane plus soil carbon sequestration were measured along a ten-point management intensity gradient in southwest Michigan. Gas fluxes were measured in situ using the static chamber method. Soil carbon measurements were made to 1-m. Preliminary results show that nitrous oxide fluxes were highest in the annual cropping systems and alfalfa perennial system, and lowest in the poplar and successional systems. Methane oxidation was highest in the mature forest, next highest in successional systems, and lowest in the annual crops and alfalfa systems. Carbon sequestration was highest in the successional systems and perennial alfalfa, and lowest in the conventionally-tilled agricultural system. Results can be used to inform landscape and regional scale predictions of changes in global warming potentials due to changing land use and agricultural management. The intensity with which agricultural systems are managed can change a number of aspects of ecosystem service provisioning, including nitrogen retention, greenhouse gas mitigation and production, and carbon sequestration. With the growing awareness of the environmental impact of humans, land managers are increasingly trying to reduce degradation while maintaining profitability. We tested the impact of management intensity on the level of nitrous oxide production, methane oxidation, carbon dioxide production, and carbon sequestration. We hypothesize that greenhouse gas fluxes will be sufficiently different among management levels that these management changes can be directly linked to changes in global warming potentials. TreatmentManagement ConventionalC-S-W rotation, chisel plowed, receives conventional levels of fertilizer and pesticides. No-TillC-S-W rotation, no-till, receives conventional levels of fertilizers and pesticides. Reduced InputC-S-W rotation, chisel plowed, with a winter leguminous cover crop, receives 1/3 pesticides and 1/3 nitrogen inputs of conventional treatment. OrganicC-S-W rotation, chisel plowed, with a winter leguminous cover crop, receives no pesticides or N-fertilizer. Poplar TreesPlanted to a fast growing Populus clone on a 10 year rotation cycle, receives no chemical inputs. AlfalfaA perennial stand that is harvested 3-4 times a year, receives fertilizer and pesticide treatments as necessary. Successional Field Native successional treatment, abandoned after spring plowing in 1989, burned annually since. TreatmentAverage Nitrogen Inputs in kg N/ha CornSoybeansWheat Conventional130.3068.5 No-Tillage130.3069.5 Reduced Input27.9 kg/ha + Cover crop 039.6 kg/ha + Cover crop OrganicCover crop0 Table 1. Treatment descriptions for the LTER ecosystems. Figure 1. Layout of the KBS LTER main site experiment. Table 2. Nitrogen fertilizer rates for the annual cropping treatments. Figure 2. Average monthly precipitation for KBS LTER site (n=18 years). Question 3: How does carbon flux vary across a management intensity gradient? Figure 4. Methane fluxes across the management gradient over the period 1993- 1997 for CF and SF, and 1991-2002 for all other treatments. Bars represent mean fluxes (+ se, n=3 or 4 replicate blocks) collected using static flux chambers once in March and twice monthly from April through September, then again once monthly until the ground was frozen. Figure 6. Geo-referenced locations of 1m soil cores taken from the KBS LTER main site during the 2001 growing season. Soil and GPS data points are archived for future analyses. Figure 7. Deep-core hydraulic soil probe and extracted, intact core contained within a transparent sleeve. Note (inverted) soil profile taken from a native deciduous forest. Figure 5a: Carbon dioxide fluxes (top left) across the management gradient over the period 1993-1997 for CF and SF, and 1991-2002 for all other treatments. Bars represent mean fluxes (+ se, n=3 or 4 replicate blocks) collected using static flux chambers once in March and twice monthly from April through September, then again once monthly until the ground was frozen. Figure 5b: Soil organic carbon (bottom left) across the management gradient, to a depth of 1 meter. Bars represent total profile C (n=3-6 replicate blocks). Five 7 cm diameter x 1 m cores were removed from each treatment plot in 2001, separated by horizon, and analyzed for bulk density and total C after first removing carbonate C by acid extraction (Figures 6,7). Question 1: How does nitrous oxide flux vary along the management intensity gradient? The highest nitrous oxide production was in the annual cropping systems, alfalfa, and coniferous forest, which did not significantly differ from one another. This may be reflective of the high variability that is typical of nitrous oxide production. This suggests that cropping system and disturbance may not be the definitive determinates of nitrous oxide production, but instead availability of nitrogen. Nitrous oxide production was lowest where soil nitrate levels were low (data not shown). Nitrous oxide production thus increased with management intensity (Figure 3). Question 2: How does methane flux vary along the management intensity gradient? Methane oxidation was highest in the forested systems, while the agricultural systems showed the lowest levels of methane oxidation (Figure 4). Early and mid- sucessional fields show values that are intermediate between the agricultural and forested systems, suggesting that some transition or community succession is required in the microbial community to transition between highly managed ecosystems (ie. agricultural) and native systems (ie. forests). Question 3: How does carbon flux vary across a management intensity gradient? Carbon dioxide production was the highest in the successional systems, while the conventional, no-till, and reduced-input systems were significantly lower than all other systems (Figure 5a). This may be due to lower levels of active fractions of the soil carbon and litter which are subject to decomposition in these systems. Soil carbon (Figure 5b) was higher in successional systems than in the annual cropping systems, which might be reflective of the higher carbon dioxide fluxes in these systems. However due to high variability, patterns across the management gradient are hard to substantiate, and further research is needed to better understand these patterns. Figure 3. Nitrous oxide fluxes across the management gradient over the period 1993- 1997 for CF and SF, and 1991-2002 for all other treatments. Bars represent mean fluxes (+ se, n=3 or 4 replicate blocks) collected using static flux chambers once in March and twice monthly from April through September, then again once monthly until the ground was frozen.