Research
Current projects
SOCnet: Long-term, on-farm soil organic carbon (SOC) monitoring network in the Upper Midwest
Agroecosystem management practices such as tilling, cover cropping, and ruminant grazing can affect soil organic carbon (SOC) levels and overall soil health. Such changes in SOC can take years to detect, and changes near the soil surface may be different than the changes in deeper soils. SOCnet is collecting soil samples over the course of nine years on working farms across Wisconsin, Iowa, and Minnesota with the goal of quantifying long-term changes in shallow and deep SOC storage on a range of soil types. The information will be valuable for the emerging farm carbon crediting programs and will help farmers manage field for SOC and soil health in the Upper Midwest. SOCnet is a collaboration between partners at the University of Wisconsin-Madison, Iowa State University, and the University of Minnesota.
Dairy Soil and Water Regeneration Project: Soil greenhouse gas emissions and soil health of dairy forage systems
Manure application, tillage, and cover cropping are important management factors in dairy forage cropping system that can impact soil greenhouse gas emissions, soil health, soil organic carbon (SOC), and soil water infiltration. Emerging manure solid products may provide additional soil and water benefits compared to typical liquid dairy manure, but little work has been done to evaluate these recent manure technologies. The Dairy Soil and Water Regeneration Project (DSWRP) is evaluating the effect of improved field and manure management practices on critical soil metrics including greenhouse gas emissions and SOC. The DSWRP is led by the Dairy Research Institute and the Soil Health Institute with six other academic partners in addition to UW-Madison.
Past projects
High-frequency N2O, CH4, and CO2 soil fluxes in bioenergy cropping systems
N2O and CH4 are potent greenhouses gases that can be exchanged between the soil and atmosphere, but intermittent survey measurements are typically used to measure these fluxes. As such, current annual soil gas budgets rely on interpolation of sparse data points and are likely to miss extreme flux events. We are using a Picarro G2508 cavity ring-down spectrometer to measure soil greenhouse gas fluxes at ten-minute intervals in a sorghum-soybean bioenergy crop rotation in central Illinois. These datasets will help us to better constrain annual greenhouse gas budgets and will improve our ability to predict soil gas fluxes in bioenergy cropping systems.
Autotrophic and heterotrophic soil respiration in sorghum and soybean
Autotrophic respiration from roots and heterotrophic respiration from microbes represents two distinct sources that comprise total soil respiration, and thus isolating the two sources is critical for developing ecosystem carbon budgets and balances. We are using two methods, root exclusion and natural abundance 13CO2, to partition autotrophic and heterotrophic soil respiration at high-frequency. CO2 concentration and isotope ratios are measured in real-time, in situ using a Picarro G2201-i cavity ring-down spectrometer. The results of this experiment will allow us to better resolve the soil carbon balance and will help us understand the drivers of autotrophic and heterotrophic soil respiration.
Root exudation in sorghum, miscanthus, and maize
Root exudates are known to influence rhizosphere processes, and exudation is thought to consume a substantial proportion of the carbon fixed by photosynthesis. Yet, we currently lack in situ measurements of root exudation in bioenergy cropping systems such as sorghum and miscanthus. To address this knowledge gap, we are collecting root exudates and measuring extracellular soil enzyme activities at multiple times throughout the growing season. Our results will improve our basic understanding of rhizosphere dynamics and will be used to inform process-based bioenergy cropping system models. This work is published in Plant and Soil.
Decomposition of elevated-lipid content sugarcane biomass
Sugarcane with high lipid content is an ideal feedstock for bioenergy products. However, we currently have a limited understanding of how the unharvested sugarcane biomass in leaves and roots will affect ecosystem C and N cycling. We are using stable isotopes to trace C and N from decomposing biomass in soil pools and greenhouse gas fluxes.
Ecosystem carbon balances in maize and switchgrass bioenergy cropping systems
The annual ecosystem carbon balance is the difference between organic carbon inputs and outputs, thereby providing an estimate of net organic carbon accrual or loss. I am using two methods – one based on biomass increments and one based on net photosynthesis – to estimate the annual ecosystem carbon balance in maize and switchgrass bioenergy cropping systems in southern Wisconsin. The results are expected to inform biofuel feedstock decision making and will also provide a novel comparison between two independent methodologies.
Seasonal and diurnal controls on autotrophic soil respiration in maize and switchgrass
Autotrophic CO2 respiration from roots represents a significant loss of carbon from terrestrial ecosystems, yet the controls on autotrophic respiration are not well understood. I am using semi-weekly and diurnal autotrophic soil respiration measurements during the growing season to investigate the relative influence of soil temperature and canopy photosynthesis on seasonal and diel patterns of autotrophic soil respiration. These results are expected to improve the performance of ecosystem-scale biogeochemical models.
Effects of soil microclimate on heterotrophic soil respiration
Soil temperature and moisture are known to have a strong influence on heterotrophic soil respiration (i.e. soil organic carbon decomposition). Plant and management factors may influence on soil temperature and moisture regimes, which in turn would affect soil organic carbon decomposition via heterotrophic respiration. For example, temporal differences in the size of the plant canopy (i.e. leaf area index) could lead to large seasonal differences in soil temperature. To assess this, we measured soil temperature, soil moisture, and heterotrophic respiration through two years in maize and switchgrass. We found clear seasonal differences in soil microclimates between the two cropping systems, and the heterotrophic respiration temperature and moisture responses suggested that the microclimate could significantly affect annual carbon loss via heterotrophic respiration. The full results have been published in Agricultural and Forest Meteorology.
Mechanisms of short-term soil organic carbon change
Soil organic carbon is physically protected from decomposition through occlusion within aggregates and sorption onto mineral surfaces. We used a density-based fractionation method to examine five-year changes in physically protected and unprotected SOC in four bioenergy cropping systems at two sites with contrasting soil texture. We found that changes were most prominent in the aggregate-associated fraction, with gains occuring under a poplar system at the site with fine-textured soils and losses occuring under no-till maize, switchgrass, and prairie at the site with coarse-textured soil. Changes in the aggregate-associated fraction were related to litter quality (C:N), and changes in the mineral-associated fraction were related to litter quantity and litter quality. Our results suggest that increasing the quantity and quality of litter inputs to soil will help to build protected soil organic carbon. This study has been published in Biogeochemistry.
Vertical distribution of belowground biomass, production, and decomposition
Relatively little is known about how belowground production and decomposition change from near the soil surface to the deeper soil horizons. Vertically-explicit soil carbon models usually assume that belowground production is vertically distributed identically to belowground biomass and that belowground decomposition decreases with soil profile depth. However, few studies have experimentally tested these dynamics. We measured belowground biomass, production, and decomposition at 0-10, 10-20, 20-30, and 30-40 cm in tallgrass prairie soil profiles. We found that belowground production was distributed relatively more deeply than belowground biomass, likely due to the slow turnover of near-surface rhizomes. We also found that belowground biomass decomposition decreased by nearly 50% from the 0-10 to 30-40 cm depths. While our results support the use of decreased decomposition with depth in biogeochemical models, more research is needed to understand the mechanisms underlying this phenomenon. This work is published in in Pedosphere.
Ecosystem-scale controls on net ecosystem carbon balance in restored tallgrass prairie
Although tallgrass prairie restorations typically accrue carbon, the magnitude of carbon sequestration varies widely among restorations. While soil texture and moisture are often cited as important edaphic factors affecting carbon sequestration, the mechanisms underlying such relationships are not well known. We used a biometric net ecosystem productivity (NEP) approach to examine how edaphic properties influenced NEP and the processes underlying NEP. We found that NEP was negatively related to soil organic carbon (SOC) and positively related to sand content. The effect of sand content was on NEP was due to greater root production in sandier soils, while the effect of SOC was due to greater soil respiration in high SOC soils. Soil moisture also had a smaller effect on soil respiration, with lower respiration in wetter soils. Overall, our results indicate the greatest potential for carbon sequestration in low SOC and wet prairie restorations. This work has been published in Restoration Ecology.
Topographic effects on biomass yield in row crops and tallgrass prairie
Soils that are seasonally wet may be marginal for annual row crop agriculture but may be prime for the production of perennial cellulosic biomass crops for biofuels. We examined the effect of topographically-induced patterns of soil moisture on yields in maize, wheat, and tallgrass prairie. Whereas maize and wheat yields were reduced by more than 60% in seasonally wet lowlands compared to uplands, tallgrass prairie yields were statistically similar between uplands and lowlands. In addition, we found that harvest efficiency increased with the proportion of graminoids in the prairie, indicating that graminoids can be used to maximize harvestable biomass. The results of this project have been published in Agronomy.
Soil moisture controls on soil organic carbon stocks in restored tallgrass prairie
Seasonally wet soils typically accrue organic carbon (SOC) more quickly than dry soils. However, whether this phenomenon is due to greater carbon inputs (i.e. more plant growth), lower carbon inputs (i.e. slower decomposition), or some combination of both factors was not known. We examined the patterns of fine root production and decomposition across a gradient of soil moisture within tallgrass prairie restorations. Our results showed that root decomposition was lower in wet compared to dry soils, but that root production did not vary systematically across the gradient, therefore indicating that greater SOC in wet soils was due to lower carbon outputs via decomposition rather than greater inputs via plant production. This work has been published in Agriculture, Ecosystems & Environment.
