IMPACTS OF CROP RESIDUE REMOVAL FOR BIOFUEL ON SOILS

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 1005779
• Multistate No.: NC-_old1178
• Project Start Date: Jan 15, 2015
• Project End Date: Sep 30, 2019
• Program Code: [(N/A)]- (N/A)

Recipient Organization
MICHIGAN STATE UNIV
(N/A)
EAST LANSING,MI 48824

Performing Department
Plant, Soil and Microbial Science

Non Technical Summary
The link between rising atmospheric CO2 concentrations and global climate change makes it increasingly important that we find ways to minimize soil CO2 emissions and sequester carbon (C) in terrestrial ecosystems. Because soils contain the largest near surface reservoir of terrestrial C, and much of this C has been lost during agricultural conversion (Schlesinger 1997), soils have a high potential for C sequestration (USDOE 2011; Lemus & Lal 2005). Highly productive bioenergy cropping systems represent one possible way to increase soil C sequestration that have the added benefit of reducing C emissions associated with fossil fuel consumption (Liebig et al. 2005; Lemus & Lal 2005; Hansen et al., 2004). However, biofuel crops likely vary in their capacity to enhance soil C sequestration. Corn, for example, is currently the most common biofuel crop but its capacity to sequester C is much lower than that of perennial grasses such as switchgrass (Panicum virgatum), miscanthus (Miscanthus spp.) and native prairie grasses such as big blue stem (Andropogon gerardii; Liebig et al. 2005; Zan et al. 2001). Perennial grasses have been observed to enhance soil C stocks within several years when cultivated in degraded soils, or in comparison to conventional agricultural systems like corn (Haney et al. 2010; Liebig et al. 2005; Hansen et al. 2004; Zan et al. 2001; Potter et al. 1999). While we know that perennial grasses can increase soil C concentrations, the mechanisms underlying these increases are not known. What we do know is that reported increases in soil C stocks must originate primarily from belowground inputs because most aboveground material is harvested in biofuel systems. Indeed, perennial grasses may have a higher potential for C sequestration than corn because the root:shoot ratios of these grasses are much higher (e.g. switchgrass 1.5 versus corn 0.2), so their below ground contributions from both dead roots and root exudates are greater (Liebig et al. 2005; Hansen et al. 2004). In addition to producing greater root biomass, perennial grass roots typically go deeper than corn roots, which likely explains some of the reported increases in deep soil C in biofuel cropping systems (>30 cm; Liebig et al. 2005; Hansen et al. 2004; Zan et al. 2001). While it seems clear that under some conditions perennial grass bioenergy cropping systems can increase soil C stocks, and that this is likely due to high levels of below-ground productivity, the mechanisms of formation, stability and longevity of root-derived soil C are poorly understood. The goal of this research is to examine the cycling and stabilization of root-derived C under different perennial biofuel cropping systems.

Animal Health Component

10%

Research Effort Categories

Basic

90%

Applied

10%

Developmental

0%

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
101	0110	1070	100%

Knowledge Area
101 - Appraisal of Soil Resources;

Subject Of Investigation
0110 - Soil;

Field Of Science
1070 - Ecology;

Keywords

soil carbon

bioenergy feedstocks

microbial activity

perennial grasses, switchgrass, miscanthus

soil aggregation, aggreate stability

Goals / Objectives
Evaluate the impact of intensifying agroecosystems inputs (e.g., cover crops, perennial crops) on maintaining/enhancing soil organic C, soil quality, productivity and the environment.

Project Methods
We have established at the Michigan State University, Kellogg Biological Station (KBS) a long term, 8-treatement experiment corresponding to a biodiversity/management intensity gradient. Treatments include continuous corn, with and without cover crops; and a corn-soybean rotation (every entry point each year) with cover crops. Each treatment is replicated in 5 randomized complete blocks, with 30m x 40m plots. All treatments host a fertilizer split-plot treatment and include a corn stover removal split-plot. The plots are on well-drained, moderate-fertility, typic hapludalf soil.When sampling, three soil cores will be collected from center of each plot/treatment with a 120-cm long, 6-cm diameter solid steel sampling tube containing a 5.7-cm acetate contamination liner to a recommended minimum depth of 1 meter (sampling depth may depend on thickness of soil root zone and presence or absence of carbonates). In the laboratory, the cores will be cut into 5-cm, 15-cm, or 30-cm sections and core bulk density will be determined on each section. Each core section will constitute one soil sample. The soils will be air-dried and crushed to pass a 2-mm screen. The soil profiles will be described using standard procedures and sampled as described above.Particle-size analysis, pH, bulk density, total C, particulate organic matter (POM), and SIC (if carbonates are present) or SOC (if carbonates are not present), and moisture at time of sampling will be completed for each sample. A minimum of three cores will be collected per treatment to compensate for soil variability within the local study area. No less than two cores will be collected per treatment to account for variability. Preference will be given to section the cores by defined depth increments rather than by horizon because it is simpler to later compile the data to calculate C mass in the soil. Horizons are not the same thickness from plot to plot or treatment-to-treatment. The depth increments will not be less than 5-cm and will be selected based on the soils and treatments being studied. Ideally, the first one or two increments from the surface should be 5-cm because of the expected rapidly changing differences due to management practices. Deeper in the profile, the increments will be at least 15-cm.Addition of cover crops and perennials to intensified agroecosystems may have more rapidly change concentration of labile C fractions or POM than on total C, a detailed characterization of SOC components will be done. Analysis of coarse and fine POM will be performed on the whole soil and aggregates following the procedures outlined by Cambardella and Elliot (1992).All the cores collected from a given study will have the same depth increments for ease of comparing treatment effects. Approximately 10-15 g subsamples will be further ground to pass a 100 mesh screen for C analysis. The C content of soils will be adjusted for soil bulk density and reported as kg C /m3 or Mg C/ha/m if sampled to 1 meter and as kg C /m2/ root zone depth or Mg C/ha/root zone depth if carbonates are present. A procedure manual will be developed to accommodate regional soil (such as presence or absence of carbonates) and weather differences to insure as much uniformity in sampling procedure and laboratory analyses as possible.In addition, other soil quality indicators such soil aggregate stability (Guzman and Al-Kaisi, 2011) and microbial biomass C (Horwath and Paul 1994) will be determined. The soil will sieved through 8-mm sieve at filed moisture condition and left to air dry on brown paper. Aggregate fractions can be separated by wet sieving or dry sieving with set of sieves range between 4 to 0.053 mm in diameter. Soil C will be evaluated for each fraction size. Aggregate associated C will be based on sand-free fraction by determining sand content for each aggregate faction size. The soil samples for microbial biomass will be collected for the top 15 cm. Soil samples can be collected using hand probe. The soil samples will be kept in 4o C if they are not processed immediately in the same day. Microbial biomass C will be determined by using the procedure by Horwath and Paul (1994).In addition, microbial acitivty, which drives C accrual versus depletion, will be assessed in each treatment and in at least two different aggregate size fractions. We will assess microbial activity in two ways, via extracellular enzyme activity (EEA) and respiration rates. We will measure EEA associated with C, N and phosphorus (P) acquisition. This includes measurement of the enzymes β-glucosidase, cellobiohydrolase, N-acetyl-β-glucosaminidase, leucine amino peptidase, urease, acid phosphatase, phenol oxidase and peroxidase. We will follow the protocol described by Tiemann and Billings, (2011). Briefly, we will homogenize soils in 50 mM sodium acetate buffer that has been adjusted to an average site pH. The resulting soil slurries will then be pipetted into 96-well microplates into which I will add fluorescently labeled substrates corresponding to the above enzymes (except urease and oxidases). Enzyme activity rates are calculated as the accumulation through time of the fluorescent label, either methylumbelliferone (MUB) or methyl coumarin (MC) or in the case of urease and the oxidases, the color change associated with [NH4+] or the break-down of the substrate 3,4-dihydroxy-L-phenylalanine (L-DOPA). After substrate addition, soils will be incubated at 25° C for ~18 h before fluorescence, with 365 nm excitation and 460 nm emission filters, or absorbance at 610 or 460 nm, is determined on Multiskan Ascent and Fluoroskan plate readers (Thermo Fisher Scientific, Inc.).Soil respiration will be measured by adding 10 g field moist soil from each sampling location to 100 ml serum bottles. Soil respiration rates will be measured every 2-3 days over the course of two weeks. To do this we will first fit bottles with septa, then use a needle and syringe to remove a 5 ml gas sample that will be immediately injected into an infra-red gas analyzer (LI-820, Li-Cor Inc., Lincoln, NE). Capped bottles will be incubated at 25° C for at least two hours before a second gas sample is withdrawn and analyzed. The difference in CO2 concentration between these two sampling times will be used to calculate a respiration rate. Respiration rates are then integrated over the course of the two-week incubation in order to calculate total C respired (Tiemann & Grandy, 2014).Treatment effects on aggregate proportions, aggregate mean weight diameter (MWD), aggregate stability, total C and N, POM C and N, microbial biomass C and N, EEA and total C respired will be determined using one-way ANOVA (SAS PROC MIXED, SAS Institute, Cary, NC) with cropping system as the fixed effect and block as a random effect (when significant). When appropriate, data will be analyzed separately by aggregate size fraction. When more than one site is considered, data will be analyzed via two-way ANOVA with cropping system, site and cropping system*site as the main effects. EEA data can also be analyzed via factor analysis on normalized data followed by analysis of factor scores by site, by treatment and by aggregate size fraction via ANOVA as described above. Correlation analyses (SAS PROC CORR) will be used to assess relationships between the measured variables.

Progress 01/15/15 to 09/30/19

Outputs
Target Audience:The target audience reached with results from research conducted during the current reporting period includes producers and stakeholders involved in row crop agriculture and forestry, more specifically potato, corn and Christmas tree producers and related stakeholders. Additionally, the audience includes scientists working in a multitude of disciplines, including microbial ecology, soil biogeochemistry, microbiology, international agriculture, and soil sciences. The research has also been disseminated to undergraduate students by using examples in teaching and involvement of undergraduate lab assistants in all aspects of the research. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?The project has involved one graduate student and one technicians. These opportunities include training in new techniques, lab protocols and instrumentation; presentation of research ideas and results to various peer groups and project teams, at regional or national scietific meetings or to grower and stakeholder groups. How have the results been disseminated to communities of interest?The results of the work have been disseminated to producers and stakeholders locally in Michigan, through presentations at winter meetings of the Michigan Potato Industry Commission and the Soil Ecology Society Meeting. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? In an experiment focused on the belowground effects of cover crop diversity at the Montcalm Research Center (MRC), part of Michigan State University AgBioResearch, there are 8 cover crop treatments including: 1) annual ryegrass (AR); 2) cereal rye (CR); 3) hairy vetch (HV); 4) Austrian winter pea (AWP); 5) AR with HV; 6) CR with AWP; 7) all four cover crops together and; 8) a no cover crop control. Soil sampling is done throughout the year, but primarily between harvest and planting when activity of cover crops or degradation of cover crop residues is greatest. We have found that 2 cover crop species (representing 2 different plant functional groups) has the greatest benefit with regards to building soil organic matter and nitrogen provisioning to cash crop.

Publications

• Type: Journal Articles Status: Accepted Year Published: 2019 Citation: Petipas, R. H., McLachlan, E., Bekkerring, C., Bowsher, A., Jack, C., White, R.A., Younginger, B., Tiemann, L. K., Evans, S. and Friesen, M. L. (in press). Interactive effects of microbes and nitrogen on Panicum virgatum root functional traits and patterns of phenotypic selection. International Journal of Plant Sciences. In press.

Progress 10/01/17 to 09/30/18

Outputs
Target Audience:Target audience reached includes soil scientists, farmers and producers, Agribusiness representatives and crop and soil science students. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?The projects have provided training opportunities for graduate students, undergraduate students and technicians who are between undergraduate and graduate studies. These students have had the opportunity to learn about methods for soil health assessment and to present results to farmers and other stakeholders at field days and national meetings. How have the results been disseminated to communities of interest?Results from these studies been presented at local field days and commodity group meetings and nationally at scientific meetings as well as the Soil Health Institute Annual Meeting. What do you plan to do during the next reporting period to accomplish the goals?Projects will continue and additional data will be collected. Changes in soil organic matter (soil carbon) are slow, therefore mulitple year studies are nessecary to determine how management changes, such as addition of cover crops, will have an impact.

Impacts
What was accomplished under these goals? Across several projects we are collecting data that will help us better understand links between agroecosystem diversity or rotational diversity and soil health, with an emphasis on soil organic matter (a.k.a. soil carbon). In natural systems, high levels of biodiversity generally confer increased productivity and resiliency. This extemds to soils where enhanced diversity can also bolster soil resiliency, and improve soil services by increasing microbial community activity and diversity. We have found that increasing cropping system diversity through the addition of multiple cover crops has a positive impact on soil health parameters. Specifically, we find that increased diversity through the addition of cover crops increases soil organic matter, microbial activity, and reduces nitrogen loss through a tightening of the nitrogen cycle and more efficient internal nitrogen provisioning.

Publications

• Type: Journal Articles Status: Published Year Published: 2018 Citation: Bowsher, A.W., Evans, S., Tiemann, L.K. and Friesen, M.L., 2018. Effects of soil nitrogen availability on rhizodeposition in plants: a review. Plant and Soil, 423(1-2), pp.59-85.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: Jilling, A., Keiluweit, M., Contosta, A.R., Frey, S., Schimel, J., Schnecker, J., Smith, R.G., Tiemann, L. K. and Grandy, A.S., 2018. Minerals in the rhizosphere: overlooked mediators of soil nitrogen availability to plants and microbes. Biogeochemistry, 139(2), pp.103-122.
• Type: Journal Articles Status: Accepted Year Published: 2018 Citation: Ouyang, Y., Evans, S. A., Friesen, M. L. & L. K. Tiemann (in press). Effect of nitrogen fertilization on the abundance of nitrogen cycling genes in agricultural soils: A meta-analysis of field studies. Soil Biology and Biochemistry

Progress 10/01/16 to 09/30/17

Outputs
Target Audience: Nothing Reported Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals?Over the next reporting period new funding sources will allow for expansion of research into focus on soil C. Specifically, two new project will begin in the spring of 2018. 1) We will assess microbial activity associated with soil C pools under different levels of protection within soil aggregates. We hypothesize that soils with greater micro-scale heterogeneity will exhibit larger soil C stocks because of protection inside the aggregates and in association with mineral surfaces. Approach: We will assess soil aggregate distribution in different bioenergy crops across soil depths and topographic positions, including C4 annual grass crops, switchgrass, and restored prairie. 2) Conduct mesocosm experiments to assess the importance of root-microbeinvertebrate interactions for building and stabilizing soil C in switchgrass in monoculture, switchgrass growing within mixed species prairie, and energy sorghum. In conjunction with microbial measurements (e.g. extracellular enzyme activities, respiration rates) that characterize C and N cycling rates, we can assess how invertebrates alter plant belowground C allocation and chemistry, with indirect effects on microbial community activities and structure, and soil C accrual. Approach: Belowground productivity, root exudation, and subsequent microbial responses in situ will be measured using a 13C pulse-chase approach in mesocosms deployed in the greenhouse to isolate a single plant. Experimental additions of nitrogen and/or invertebrates (see above) prior to the pulse-chase will reveal nutrient and food-web interactions. Once the 13C label has been introduced, it can be used to identify and chemically characterize root exudates and to isolate microbes activelyutilizing root exudates via stable isotope probing.

Impacts
What was accomplished under these goals? No research was conducted under this specific goal during the current reporting period. Research on the potential for improving soil health using non-perennial cover crops has been conducted but the focus was not specifically on soil C. Cover crop and perennial grass system research includes: 1) Two lab soil incubation studies have been completed with data analysis and manuscript preparation underway. One project forms the core of a Master's thesis. For each experiment, cover crop residues were collected on-farm including legumes or grasses and used in laboratory incubations of soils collected from: 1) three differently managed potato farms and; 2) a nutrient gradient experiment in which a corn-soy-wheat rotation is fertilized with different levels of N, from 0 to 220 kg/ha. Results summary: Thus far, in the first incubation we see that potato system management has large impacts on the way microbial communities process cover crop residues. On farms where management practices are chosen that can improve soil health and soil biotic activity, we see much faster decomposition rates and greater N release. Key outcomes: Data sets are currently being analyzed or have been analyzed and a Master's Thesis and publications are currently in preparation. Additionally, the work has been presented to Michigan potato producers and other growers at the Midwest Cover Crop Council meeting, and to a broader scientific community at the Soil Ecology Society meeting in 2017. 2) In August 2015, at the MSU Montcalm Research Center, I have established an experiment that consists of a randomized block of five replicates of eight different cover crop and cover crop mixture treatments - legume and grass mixes. Data: The soils and data collection are still ongoing, with cover crops interseeded into corn in late July 2017. Results Summary: Legume-grass, 2-species mixtures have increased total soil C compared to no cover crops, monoculture or four species cover crop mixtures. Two species cover crop mixtures also produced the greatest amount of biomass in fall 2016. Key outcomes: The potential benefits of cover crops towards this goal cannot be realized until we have a better understanding of how they impact whole cropping systems. 3) Research focused on understanding how the rhizosphere microbiome associated with perennial biofuel crop systems in marginal lands mediate N transformations. Accomplishments: Field and greenhouse experiments are currently underway. Field data collection for the 2017 growing season data across six experimental sites in Michigan and Wisconsin situated on marginal or low productivity/low fertility soils has been completed. Data: Over the past reporting period, data collection includes monitoring plant productivity, plant physiological traits, soil N transformation processes, N-availability, and microbial genomics and transcriptomics related to soil N-transformations at all six research sites. The collection of soils and data are still ongoing for both field and greenhouse experiments. Results Summary: No results to summarize at this time; data analysis and continued collection is currently underway. Key outcomes: The preliminary results have been presented at the 2016 American Geophysical Union and the 2017 Soil Ecology Society meeting, both as part of a graduate student's dissertation research.

Publications

Progress 10/01/15 to 09/30/16

Outputs
Target Audience:The target audience reached includes producers and stakeholders involved in row crop agriculture and forestry, more specifically potato, corn and Christmas tree prodcution. Additionally, the audience includes scientists working in a multitude of disciplines, including microbial ecology, soil biogeochemistry, microbiology, international agriculture, and soil sciences. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?The project has involved opportunities for training professional development two graduate students and a post doc. All students and post docs involved in this work have been trained in new techniques, lab protocols and instrumentation and have had the opportunity to present research ideas and preliminary results to various peer groups and project teams. How have the results been disseminated to communities of interest?The results of this work have been disseminated to producers and stakeholders locally in Michigan, through presentations at field days, including MSU Ag Innovations Field Day and at meetings of the Michigan Potato Industry Commission. Work has also been presented to producers and stakeholders nationally and internationally through a published MSU extension bulletin and invited presentations at antional and international meetings. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? IMPACTS: This research is important in the context of soil sustainability and productivity. Food production has doubled in the last 40 years, mainly due to improved crop varieties, more effective pest resistance, greater water subsidies and increased fertilizer inputs, but in order to keep pace with human population growth, food production must again double in the next 40 years. A large proportion of land suitable for agriculture is already in use so we must look for other means of increasing crop production to meet future demands. One of the ways in which we can begin to meet future demands, while simultaneously creating more sustainable agricultural systems, is by focusing on soil health. One critical aspect of a healthy soil is nutrient provisioning or the ability to provide nutrients in support of plant growth. This research provides information about microbial communities and their contributions to organic matter decomposition and soil organic matter (SOM) formation that is critical for understanding soil health and more specifically, nutrient provisioning. Understanding the controls on SOM break-down and formation is critical because SOM is the foundation of a healthy, fertile soil, driving multiple soil functions. In addition to storing the largest fraction of terrestrial organic carbon and acting as a nutrient reservoir, SOM influences soil structure, water holding capacity, pH, ion exchange capacity, and soil biological activity. All of these factors in turn determine soil fertility, or the ability of soils to provide water and nutrients in support of plant growth. These data will ultimately help us design management practices that effectively optimize microbial contributions to crop nutrient availability and use efficiency. GOAL 1: Determine how the initial chemistry and chemical complexity of cover crop residues and other organic amendments affect microbial community activity and SOM stocks. Experiments: There are two experiments related to this goal, one completed and one in progress, which a Master's student is conducting. For each experiment, cover crop residues were collected in the spring including legumes such as alfalfa, field pea, clover and hairy vetch, or grasses such as rye, millet, oats and wheat. The residues were used in laboratory incubations of soils collected from: 1) three different farms that use different strategies for managing potato production fields and; 2) the MSU Kellogg Biological Station nutrient gradient experiment in which a corn-soy-wheat rotation is fertilized with different levels of N, from 0 to 220 kg/ha. In each incubation, residues and residue mixtures were added to soils. The first soil incubation lasted for 90 days and the second will be completed after 360 days. Data collected: Over the course of these two incubations we have collected soil respiration rates every few days, and have sub-sampled soils at several time points during the incubation to assess soil inorganic N content and extracellular enzyme activity. In the second incubation we also measured microbial biomass. Results summary: Data sets are currently being analyzed from the first incubation and are incomplete for the second incubation. Thus far, in the first incubation we see that potato system management has large impacts on the way microbial communities process cover crop residues. On farms where management practices are chosen that can improve soil health and soil biotic activity, we see much faster decomposition rates and greater N release. Key outcomes: These experiments will result in two peer reviewed publications and a Master's thesis. Additionally, the work will be presented to Michigan potato producers and to a broader scientific community at the AAAS meeting in the spring of 2017. GOAL 2: Elucidate N cycling dynamics and timing of plant available N in rotations with a single cover crop, cover crop combinations, and cover crops paired with other organic amendments. Experiments: In August 2016, at the MSU Montcalm Research Center, I have established an experiment that consists of a randomized block of five replicates of eight different cover crop and cover crop mixture treatments. The treatments include: 1) annual ryegrass; 2) cereal rye; 3) hairy vetch; 4) Austrian winter pea (AWP); 5) annual rye and hairy vetch; 6) cereal rye and AWP; 7) annual ryegrass, cereal rye, hairy vetch and AWP; and 8) no cover crop. Data collected: The soils and data collection are still ongoing to determine soil moisture, water stable aggregates, microbial extracellular enzyme activity and plant available N. Results Summary: No results to summarize at this time; soil and data collection is currently underway. Key outcomes: A major goal of cover crop research is to identify how cover crops can be used to build environmental capital at an economically low cost. Achieving this goal requires that crop productivity be maintained at a high level while ensuring soil and system sustainability. The potential benefits of cover crops towards this goal cannot be realized until we have a better understanding of how they impact whole cropping systems. GOALS 3 & 4: These goals have been replaced due to a shift in my research focus subsequent funding of a large project focused on the sustainability of perennial bioenergy cropping systems on marginal lands. Specifically, the new project will explore interactions between bioenergy plant traits, root exudation and the rhizosphere microbiome in order to identify how bioenergy crops acquire N and can be sustainably managed over time. The new research goal - understanding how the rhizosphere microbiome associated with perennial biofuel crop systems in marginal lands mediate N transformations important to plant N availability and acquire C resources from plants versus SOM to fuel N transformations. Experiments: Field and greenhouse experiments, started during the current reporting period, are being conducted to address the above goals. The primary field experiment includes six experimental sites across Michigan and Wisconsin situated on marginal or low productivity/low fertility soils. The six sites vary in soil type and chemistry, as well as climate, and all contain multiple bioenergy cropping systems. The project will focus primarily on switchgrass. A greenhouse experiment, explores differences in microbial community composition and activity under two field N regimes. Switchgrass planted into soils collected from either fertilized or unfertilized plots at one of the marginal land field sites will be destructively harvested prior to measurements of soil N fixation and N mineralization rates. Sub-samples of rhizosphere soil plus roots and the aboveground biomass will be flash frozen for DNA/RNA extraction in order to link functional measurements with microbial community structure and plant transcriptomes. Data collected: Over the past reporting period, data collection includes monitoring plant productivity, plant physiological traits, soil N transformation processes, N-availability, and microbial genomics and transcriptomics related to soil N-transformations at all six research sites. The collection of soils and data are still ongoing for both field and greenhouse experiments. Results Summary: No results to summarize at this time; data collection is currently underway. Key outcomes: The greenhouse experiment results will be presented at the 2016 American Geophysical Union meeting; be a part of a graduate student dissertation; and a peer-reviewed publication. A major goal of bioenergy research is to identify how cropping systems can be used as an economically and environmentally low-cost energy source. Perennial bioenergy cropping systems utilizing microbial N-fixation as a N-source in under-utilized marginal lands may be an ideal system to jointly maximize productivity and sustainability.

Publications

• Type: Other Status: Published Year Published: 2016 Citation: Snapp, S., L.K. Tiemann, N. Rosenzweig, D. Brainard, G. Bird. (2016) "Managing Soil Health for Root and Tuber Crops." Extension Bulletin E-3343, Michigan State University, East Lansing, MI.
• Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Tiemann, L.K. and D. Baas (August 24, 2016) Healthy Soil  Dig a Little, Learn a Lot. MSU Agriculture Innovations Day: Focus on Soils, Frankenmuth, MI.

Progress 01/15/15 to 09/30/15

Outputs
Target Audience: Nothing Reported Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Atendence of the annual committee meeting for this multi-state research group allowed me to meet colleagues who are leaders in this field and learn more about their research. How have the results been disseminated to communities of interest?Results from a study exploring effects of cropping rotational diversity (including cover crops) have been presented to stakeholders at the Michigan Agribusiness Nematology Short-course, and will be presented at the National No-Till Conference. What do you plan to do during the next reporting period to accomplish the goals?Project goals will be accomplished through a newly funded Department of Energy project that will explore soil C and N dynamics under perennial bioenergy cropping systems. The primary goals of this new project will elucidate how the rhizosphere microbiome associated with perennial biofuel crop systems in marginal lands: Mediates N transformations important to plant N availability; Acquires C resources from plants versus SOM to fuel N-transformations; Interacts with plant root exudation patterns and physiological pathways; Varies by cropping system and environment.

Impacts
What was accomplished under these goals? Biodiversity loss, an important consequence of agricultural intensification, can lead to reductions in agroecosystem functions and services. Increasing crop diversity through rotation may alleviate these negative consequences by restoring positive aboveground-belowground interactions. Positive impacts of aboveground biodiversity on belowground communities and processes have primarily been observed in natural systems. Here we test for the effects of increased diversity in an agroecosystem, where plant diversity is increased over time through crop rotation. As crop diversity increased from one to five species, distinct soil microbial communities were related to increases in soil aggregation,organic carbon, total nitrogen, microbial activity and decreases in the carbon-to-nitrogen acquiring enzyme activity ratio. This study indicates positive biodiversity-function relationships in agroecosystems, driven by interactions between rotational and microbial diversity. By increasing the quantity, quality and chemical diversity of residues, high diversity rotations can sustain soil biological communities, with positive effects on soil organic matter and soil fertility. Annual row cropping systems converted to perennial bioenergy crops tend to accrue soil C, likely a function of increased root production and decreased frequency of tillage; however very little is known about the mechanisms governing the accrual and stability of this additional soil C. To address this uncertainty, we assessed the formation and stability of aggregates and soil organic C (SOC) pools under switchgrass, giant miscanthus, a native perennial grass mix and continuous corn treatments in Michigan and Wisconsin soils differing in both texture and mineralogy. We isolated different aggregate size fractions, > 2 mm, 0.5 - 2 mm and < 0.5 mm, using a procedure intended to minimize alterations to aggregate biological and chemical properties. We determined SOC, permanganate oxidizable C (POXC), and microbial activities (i.e. enzyme activities and soil respiration rates) associated with these aggregates. Soil type strongly influenced the trajectory of aggregate formation and stabilization with differences between sites in mean aggregate size, stability, SOC and microbial activity under perennial versus corn cropping systems. At the Michigan site, soil microbial activities were highest in the > 2 mm aggregates, and higher under the perennial grasses compared to corn. Contrastingly, in Wisconsin soils, microbial activities were highest in the < 0.5 mm aggregates and evidence for soil C accrual under perennial grasses was observed only in a fast turnover pool in the < 0.5 mm aggregate class. Our results help explain cross site variability in soil C accrual under perennial bioenergy crops by demonstrating how interactions between belowground productivity, soil type, aggregation processes and microbial communities influence the rates and extent of SOC stabilization. Bioenergy cropping systems have the potential to be low-C energy sources but first we must understand the complex interactions controlling the formation and stabilization of SOC if we are to maximize soil C accrual.

Publications

• Type: Journal Articles Status: Published Year Published: 2015 Citation: Tiemann, L. K. and A. S. Grandy. (2015). Mechanisms of soil carbon accrual and storage in bioenergy cropping systems. GCB Bioenergy. 7, 161-174, DOI: 10.1111/gcbb.12126.
• Type: Journal Articles Status: Published Year Published: 2015 Citation: Tiemann, L. K., Grandy, A. S., Marin-Spiotta, E., Atkinson, E. E., and M. D. McDaniel. (2015) Crop rotational diversity enhances belowground communities and functions in an agroecosystem. Ecology Letters 18, 761-771.