Progress 03/15/18 to 03/14/23

Outputs
Target Audience:Scientists, Engineers, Farmers, USDA officials Changes/Problems:COVID-19 severely impacted the ability for our teams to conduct the husk-amendment field project in 2020 but we were able to amend fields at the end of the growing season in 2021. Therefore, the planned field experiment took place in the 2022 growing season. Additionally we had challenges in recruiting and retaining some of the project graduate and undergraduate researchers. What opportunities for training and professional development has the project provided?Three graduate students, two undergraduate students, and two postdocs have been supported by this project. Additionally, seven graduate students and 5 undergraduates worked on this project but were supported by other funds. In the Seyfferth Lab, group members participate in group meetings, which occur at least every two weeks. In these sessions, students have the opportunity to present research progress, practice presentations, and obtain feedback to improve science communication skills. Students also learn writing techniques either through formal writing courses or through editing and revising drafts that are shared with the group. In addition, students work in a collaborative environment to receive trainings on laboratory/field techniques and protocols. This model and weekly check-in meetings with Dr. Seyfferth result in successful completion of dissertation/theses with peer-reviewed publications. This project has directly contributed to 1 M.S. and 3 Ph.D. degrees in the Seyfferth Lab, and all students have published their work. Abby Evans, M.S. student in the Seyfferth group, was primarily responsible for collecting and analyzing porewater chemistry, gas fluxes, and soil/Fe plaque during the growing season in the UD paddy mesocosms. She presented her research at the ASA-CSSA-SSSA meeting and her manuscript was accepted in the Journal of Environmental Management in 2021. A postdoc in the Seyfferth lab, Matt Limmer, trained the MS student and was primarily responsible for field maintenance, probe calibration, plant analysis, and data analysis. Matt has presented at conferences, published three first-authored papers as a result of this work and has two additional manuscripts under review. Gretchen Dykes was a Ph.D. student in the Seyfferth Lab who graduated in 2021 and investigated impacts of Si amendments on microbial community composition and arsM abundance. She published two papers on this topic and presented at national and international conferences. Douglas Amaral was a PhD student in the Seyfferth lab who contributed to research that examined the impacts of water and Si-residue management on As and Cd in grain; this work resulted in a manuscript that was published in 2019. Frank Linam, another PhD student in the Seyfferth Lab, assisted with field research and has performed pot study experiments that investigates the impact of water management and rice residues on levels of As and Cd in plants; that work has resulted in one publication and several presentations of research. In the Runkle lab and at the University of Arkansas, the undergraduate, graduate students and postdocs installed sensors in the field, did weekly visits to monitor fields and measure variables such as Leaf Area Index, canopy height or floodwater depth, as well as conducted chamber measurements. They were guided by interactions with Dr. Arlene Adviento-Borbe, USDA-ARS, Delta Water Resources Management Unit, Jonesboro, AR. Dr. Adviento-Borbe and Dr. Runkle discussed safety considerations, ethics of field research, and career options with each group member as part of their professional development training. Marguerita Leavitt, an M.S. student in the Runkle group, was responsible for analyzing eddy covariance methane flux data from 2020 in the context of other years of data. She has presented research at several virtual conferences and was awarded 2nd place in MS level poster competition at the Arkansas Soil and Water Conference in January 2021 and 4th place in 2022, and she was given a Top 5 Outstanding Student Presentation Award, at the North America Carbon Program Open Science Meeting (2021). Her M.S. is now awarded (summer, 2022) and a draft manuscript is in internal review for submission to the journal Agriculture Ecosystems & Environment. Postdoc Beatriz Moreno-Garcia helped manage project implementation and oversaw undergraduates working in the field on chamber measurements and grain sampling. Postdoc Sandhya Karki analyzed gas samples by Gas Chromatography and interpreted their results, calculating seasonal emission rates. The group's former PhD student Colby Reavis (graduated 2021, now at the USDA-ARS with project partner Michele Reba) and former PhD student Bennett Barr (changed to health profession) gained insight on chamber methods and rice paddy dynamics through work on this project. The undergraduates Anthony Zadoorian, Juan Arguijo, Leo Black, Masen Wade, Sam Carroll, Connor Pearson, and Conor Germann were also trained on field and lab data collection and analysis through this project. Several have since taken positions in the public sector (ARS, NRCS), private sector (engineering consulting), or graduate school, or are working to finish their honors thesis research at the University of Arkansas. In the Reid Lab, this project directly supported the dissertation research of three PhD students (Lena Abu-Ali, Hyun Yoon, and Yi Sang), and two additional students (Ph.D. student Zihao Zhang and undergraduate student Jenna Israel) contributed to this project through assistance with field or laboratory research activities. The Reid Lab meets weekly to discuss student research progress, participate in training on laboratory or modeling methods, and to workshop the production of figures and other visualization of scientific data. Students present their work three times per year to improve their science communication skills, and also improve their technical writing skills through courses offered by Cornell University. Students have also gained skills in statistical modeling techniques, including the use of R to implement linear mixed effects models, through formal coursework and individualized consulting offered through Cornell's Statistical Consulting Unit. Lena Abu-Ali, whose dissertation was directly supported by this project, defended her dissertation in December 2022 and is now an ORISE Postdoctoral Fellow in the EPA Office of Water in Washington, DC. A manuscript based on one of her dissertation chapters is in the final stages of preparation for submission to Environmental Geochemistry and Health. Dr. Abu-Ali gave an oral presentation on her work related to this project at ASA-CSA-SSSA meeting in 2021. Dr. Abu-Ali also participated in ASA-CSA-SSSA congressional visit days in 2019 and 2020 while supported by this project, and was awarded a Future Leaders in Science Award. Ph.D. student Hyun Yoon has led research on the effects of organic amendments on As methylation activity and has strengthened his skills in biomolecular methods (e.g., RT-qPCR) and organic matter characterization methods as part of this research. This work is expected to lead to two chapters in Yoon's dissertation, and to two peer-reviewed manuscripts. PhD students Yoon and Sang both gained valuable field-based agronomic research experience as part of this project which has complemented the laboratory-based research activities in the other portions of their doctoral research. All students involved in this research also gained experience in systems thinking regarding the circular economy, and in working in and communicating with multi-disciplinary research teams through frequent zoom-based research team meetings. How have the results been disseminated to communities of interest?Results have been disseminated to scientists through presentations at the Soil Science Society of America and America Society of Agronomy meetings, the North American Carbon Program, and the Arkansas Soil and Water Conference which targeted USDA researchers, University researchers, farmers, and individuals in the Agronomic industry, congressional staffers through the SSSA-sponsored Congressional Visits Day, as well as direct conversations with farmers. In addition, 10 publications have been accepted, and a public-facing article is in press at the ASABE society magazine Resource. A list of the presentations follows: Oral Presentations Runkle, B.R.K.; Moreno-García, B.; Karki, S.; Limmer, M.A.; Sang, Y.; Yoon, H.; Linam, F.; Adviento-Borbe, M.A.A.; Reba, M.L.; Reid, M.C.; Seyfferth, A.L. Rice husk amendment and irrigation management impacts on rice growth, greenhouse gas emissions, and grain quality. Rice Technical Working Group, 2023. Runkle, B.R.K. Invited: Pathways toward sustainable, climate-smart rice production. University of Wisconsin, Madison, Climate, People, and the Environment Program Seminar, January 2023. Seyfferth, A.L. Invited: Limiting As in rice through water and Si management. University of Turin, Italy, May 2022. Moreno-Garcia, B. Invited: Sustainable rice management practices in the US. Consejo Superior de Investigaciones Científicas (CSIC), Estación Experimental de Aula Dei, Zaragoza, Spain. Virtual, January 2022. Seyfferth, A.L. Invited: Limiting As in rice through water and Si management. University of Bern, Switzerland, December 2021. L. Abu-Ali, H. Yoon, S Maguffin, J. Rohila, A. McClung, and M.C. Reid. Characterization of Rice Grown Under Traditional and Alternative Irrigation Strategies: As, Cd, and Zn Dynamics across Multiple Varieties, Growing Seasons, and Pore Water Chemical Conditions. Oral Presentation, ASA-CSSA-SSSA International Annual Meeting, Salt Lake City, Utah, US, November 7-10, 2021. Reid, M.C. Invited: Effects of Alternate Wetting and Drying on Redox Cycling of Iron and Manganese in Paddy Soils: Implications for (Im)mobilization of Arsenic. Dale Bumpers National Rice Research Center, Stuttgart, Arkansas, November 2019. Limmer, M.A., Evans, A., Seyfferth, A.L. Quantifying paint removal on IRIS films with the IRIS imager. Soil Science Society of America Annual Meeting. Salt Lake City, November 2021. Seyfferth, A.L. Invited: Combating As uptake by rice through soil Si management. Dartmouth College, NH, June 2020. Seyfferth, A.L. Invited: Linking soil science to food security: Combating As uptake by rice through soil Si management. Eidgenössische Technische Hochschule (ETH) Zürich, Switzerland, October 2019. Dykes, G.E., Chari, N., Seyfferth, A.L. Methylated arsenic dynamics in silicon-amended flooded rice paddies. Soil Science Society of America Annual Meeting. San Diego, CA. January 2019. Seyfferth, A.L., Limmer, M.A., Interactions of Silicon and Arsenic in Rice. Goldschmidt. Boston, MA. August, 2018. Poster Presentations: Moreno-García, B., Limmer, M.A., Seyfferth, A.L., Reba, M., Runkle, B.R.K. Rice Grain Metal(loid) Concentration as Affected by Management Practices. Poster Presentation. ASA-CSSA-SSSA International Annual Meeting, Salt Lake City, Utah, US, November 7-10, 2021. Linam, F., Limmer, M.A., Seyfferth, A.L. Optimizing Paddy Water Status and Rice Husk Amendment. 2021 Delaware Environmental Institute Symposium, Newark, DE, USA. March 25, 2021. Evans, A.E., Limmer, M.A., Seyfferth, A.L. Using Iron and Manganese-Coated IRIS Films to Quantify Soil Redox Potential in Rice Paddies Under Alternate Wetting and Drying (AWD) Management. Soil Science Society of America International Annual Meeting. San Antonio, TX. November, 2019. Dykes, G.E., Chari, N., Seyfferth, A.L. Silicon induces arsenite and monomethyl arsenic release from soil solids: the casus belli of microbial chemical warfare? Goldschmidt. Barcelona, Spain. August, 2019. Dykes, G.E. , Limmer, M.A., Chan, C.S., Seyfferth, A.L. Rice soil microbial communities respond to incorporation of silicon-rich soil amendments. Geobiology. Banff, Canada. June, 2019. What do you plan to do during the next reporting period to accomplish the goals?We have several publications that are in preparation that we plan to see through to publication. These are: Matt A. Limmer, Franklin Linam, Angelia L. Seyfferth. The effect of rice residue management on rice paddy biogeochemistry. In preparation. Marguerita Leavitt, Beatriz Moreno-García, Colby W. Reavis, Michele L. Reba, Benjamin R.K. Runkle. The Effect of Water Management and Ratoon Rice Cropping on Methane Emissions and Harvest Yield in Arkansas. In preparation. Lena Abu-Ali, Scott C. Maguffin, Jai S. Rohila, Anna M. McClung, Matthew C. Reid. Effects of Alternate Wetting and Drying on Oxyanion-Forming and Cationic Trace Elements in Rice Paddy Soils: Implications for Concentrations of Arsenic and Micronutrients in Rice. In preparation. Hyun Yoon, Alexandre Poulain, and Matthew C. Reid. Effects of Dissolved Organic Matter on Microbial Arsenic Transformation: The Role of Carbon Catabolite Repression. In preparation. Hyun Yoon, Ben Stenzler, Lena Abu-Ali, Maria Pilar Asta, Alexandre Poulain, and Matthew Reid. Arsenite Bioavailability in the Presence of Dissolved Organic Matter and Complexed Ferric Iron: Insights from an Anaerobic Biosensor Assay. In preparation. Runkle, B.R.K.; Moreno-García, B.; Karki, S.; Limmer, M.A.; Sang, Y.; Yoon, H.; Linam, F.; Adviento-Borbe, M.A.A.; Reba, M.L.; Reid, M.C.; Seyfferth, A.L.Rice husk amendment and irrigation management impacts on rice growth, greenhouse gas emissions, and grain quality. In Preparation.

Impacts
What was accomplished under these goals? We used laboratory, mesocosm, and field-scale experiments to address the goals of the project. To accomplish the first objective, we performed both pot and mesocosm-scale experiments in which we combined management of water (flooded to alternate-wetting and drying to nonflooded) and Si-rich amendments (rice husk, charred husk, straw, charred straw) in soil and grew rice to maturity. We then examined the impact of the management on grain yield, arsenic and cadmium levels in rice grain, localization of arsenic species in rice grain, and formation and mineral composition of iron plaque. We also used these experiments to develop a new sensor to be used as a water management tool for rice farmers. This work has resulted in 10 publications to date, with 1 more in review, 6 in preparation, and 17 presentations. We had to postpone the field experiment that was planned for 2020 due to COVID-19, but we were able to implement the Si-rich amendments in the Fall of 2021 and perform the field experiment in the summer of 2022. We are currently in the process of wrapping up data analysis for the field experiment and we plan to submit manuscripts on that work in 2023. To accomplish the second objective, we examined porewater chemistry and greenhouse gas emissions throughout the rice growth cycle from pot, mesocosm, and field-scale experiments. We utilized Rhizon samplers in pot, mesocosm, and field experiments to extract porewater from the soil and examined dissolved constituents including pH, redox potential, dissolved organic carbon, and elements including cadmium, arsenic, and arsenic species. We performed a statistical analysis of rice paddy pore water chemistry and rice grain composition to evaluate the effects of AWD on concentrations of oxyanion-forming (e.g., arsenic, molybdenum) and cationic trace elements (e.g., cadmium, zinc, copper, manganese) in rice. We found diverging effects of AWD on oxyanion-forming vs. cationic trace elements due to AWD impacts on soil pH and Fe oxide formation. This result has implications for effects of AWD on both toxic elements (As, Cd) as well as nutritionally-important trace elements (Zn, Mn). A manuscript describing this work is in preparation for submission in 2023). For monitoring greenhouse gas emissions associated with the husk amendments, we used the closed chamber technique in pot, mesocosm, and field studies as well as the eddy covariance method for CO2 and CH4 for unamended fields. These studies demonstrate that there are only negligible increases in N2O emissions from AWD, and relatively minor increases in CH4 emissions from husk amendments, especially when compared to straw incorporation. Two publications on the greenhouse gas emissions are in press or internal review for submission; one additional paper is expected to show the impact of husk amendments on these emissions in the field setting, and the statistical analysis of AWD effects on cationic and oxyanion-forming metal(loid)s has led to one oral presentation by a PhD student, and a manuscript that is in the final stages of preparation. To accomplish the third objective on the effects of amendments on biogeochemical processes regulating As methylation, we tested the effects of different rice biomass residues (rice straw; husk), along with other forms of organic matter (leachate from algae growing in rice paddy fields; commercially-available humic acid products) on arsenic methylation. A specific objective of these experiments was to distinguish effects of extracellular As-DOM complexation vs. carbon catabolite repression on microbial uptake and methylation of arsenic. Carbon catabolite repression occurs when microorganisms decrease expression of transport and catabolic enzymes in the presence of abundant labile organic carbon substrates, a phenomenon known to inhibit microbe-catalyzed chemical transformations. We combined multiple laboratory analyses, including arsM gene expression analysis, biosensor methods, and an As biomethylation assay using Arsenicibacter rosenii (a strong As methylator that was isolated from an As-contaminated rice paddy soil) to test effects of organic residue amendment on As uptake and methylation activity. Key insights from this work are: (a) Microbial uptake of As can be significantly inhibited by high concentrations of labile organic carbon, leading to lower levels of As methylation; (b) Microbial uptake and methylation of As is also significantly inhibited in the presence of DOM with high concentrations of complexed ferric iron due to formation of ternary complexes; and (c) in Fe-poor waters the organic sulfur content of DOM is a good predictor of As-DOM complexation. This work has led to two manuscripts that are in preparation, with a number of conference abstracts in review for presentations in the summer of 2023. We also examined the drivers of shifts in the arsM-bearing community due to amendments of rice husk and compared those to other Si-rich amendments in mesocosm studies. These data show that husk amendment changes the arsM-bearing community, but the shift does not always correlated with higher methylated As species in rice grain, which were driven more by low-redox conditions in soil. This work has led to 2 publications and several presentations. In addition to the goals of the project, this work has opened up new directions. In one new project, Seyfferth and Runke are collaborating to establish a framework for the mitigation of heavy metals in food with a focus on rice and spinach. https://iafns.org/a-framework-for-heavy-metal-prioritization-and-mitigation-for-reducing-metal-intake-rice-and-spinach-case-studies/ In addition, Seyfferth and Runkle are collaborating on a newly funded AFRI grant that is targeted at decreasing toxic levels of arsenic species in rice via pre and post harvest strategies. Moreover, preliminary data from this project supported a successful fellowship application for Dr. Michael Vega (Reid group) to the Cornell Atkinson Center for Sustainability Postdoctoral Fellowship program to perform multi-omics analysis on couplings between arsenic and nitrogen cycling in rice paddy soils.

Publications

• Type: Journal Articles Status: Published Year Published: 2021 Citation: Runkle, B.R.K., Seyfferth, A.L., Reid, M.C., Limmer, M.A., Moreno-Garcia, B., Reavis, C.W., Pe�a, J., Reba, M.L., Adviento-Borbe, A.A., Pinson, S.R.M., Isbell, C. Socio-technical changes for sustainable rice production: rice husk amendment, conservation irrigation, and system changes. Frontiers in Agronomy, 2021, 3:741557. https://doi.org/10.3389/fagro.2021.741557
• Type: Journal Articles Status: Accepted Year Published: 2023 Citation: Karki S, Adviento-Borbe MaA, Runkle BRK, Moreno-Garc�a B, Anders M, Reba ML (2023) Multiyear methane and nitrous oxide emissions in different irrigation management under long-term continuous rice rotation in Arkansas. Journal of Environmental Quality, in press. https://doi.org/10.1002/jeq2.20444
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Evans, A.E, Limmer, M.A., Seyfferth, A.L. Indicator of redox in soil (IRIS) films as a water management tool for rice farmers. Journal of Environmental Management, 2021, 294, 112920. 10.1016/j.jenvman.2021.112920
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Dykes, G.E., Limmer, M.A., Seyfferth, A.L. Silicon-rich soil amendments impact microbial community composition and the composition of arsM bearing microbes. Plant and Soil, 2021, 468, 147-164. 10.1007/s11104-021-05103-8
• Type: Journal Articles Status: Published Year Published: 2022 Citation: Limmer, M.A., Seyfferth, A.L. Altering the localization and toxicity of arsenic in rice grain, Scientific Reports, 2022, 12:5210. https://doi.org/10.1038/s41598-022-09236-3
• Type: Journal Articles Status: Published Year Published: 2022 Citation: Limmer, M.A., Thomas, J., Seyfferth, A.L. The effect of silicon on the kinetics of rice root iron plaque formation, Plant and Soil, 2022, 477:171-181.https://doi.org/10.1007/s11104-022-05414-4
• Type: Journal Articles Status: Published Year Published: 2019 Citation: Seyfferth, A.L., Limmer, M.A., Wu, W. Si and water management drives changes in Fe and Mn pools that affect As cycling and uptake in rice. Soil Systems, 2019, 3(3), 58. https://doi.org/10.3390/soilsystems3030058
• Type: Journal Articles Status: Published Year Published: 2019 Citation: Seyfferth, A.L., Amaral, D.C., Limmer, M.A. Guilherme, L. R. Combined impacts of Si-rich rice residues and flooding extent on grain As and Cd in rice. Environment International, 2019, 128, 301-309. 10.1016/j.envint.2019.04.060
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Limmer, M.A., Evans, A.E, Seyfferth, A.L. The IRIS Imager: A freeware program for quantification of paint removal on IRIS films. Soil Science Society of America Journal, 2021, 85, 2210-2219. https://doi.org/10.1002/saj2.20308
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Dykes, G.E., Chan, C., Seyfferth, A.L. 16S rRNA gene amplicon sequencing data from flooded rice paddy mesocosms treated with different silicon-rich soil amendments. Microbial Resource Announcements, 2021, 10, e0017821. https://doi.org/10.1128/MRA.00178-21
• Type: Other Status: Published Year Published: 2023 Citation: Runkle BRK, Seyfferth A, Reid M, Reba M, Limmer M, Moreno-Garc�a. Opportunities for the biocircular economy in rice production, Resource Magazine, ASABE, 2023.
• Type: Journal Articles Status: Under Review Year Published: 2023 Citation: Limmer, M.A., Linam, F. Evans, A., Seyfferth, A.L. Unraveling the mechanisms of Fe oxidation and Mn reduction on Mn IRIS films. In Review.

Progress 03/15/21 to 03/14/22

Outputs
Target Audience:USDA researchers, University researchers, farmers, and individuals in the agronomic industry. Changes/Problems:COVID-19 severely impacted the ability for our teams to conduct the husk-amendment field project in 2020, and in 2021. Fortunately, we were able to travel to the field site at the end of the season in 2021 to amend fields with rice husk and we are now on track to complete the field project in 2022. What opportunities for training and professional development has the project provided?Two graduate students, one undergraduate student, and one postdoc have been supported by this project. One additional postdoc and two graduate students have been working on this project but are supported by other funds. Abby Evans, M.S. student in the Seyfferth group, was primarily responsible for collecting and analyzing porewater chemistry, gas fluxes, and soil/Fe plaque during the growing season in the UD paddy mesocosms and her manuscript was accepted in the Journal of Environmental Management in 2021. A postdoc in the Seyfferth lab, Matt Limmer, trained the MS student and is primarily responsible for field maintenance, probe calibration, plant analysis, and data analysis. He has presented at conferences, published one paper on as a result of this work and has two additional manuscripts under various stages of preparation that will be submitted in 2022. Gretchen E. Dykes was a Ph.D. student in the Seyfferth Lab who graduated in 2021 but who investigated impacts of Si amendments on microbial community composition and published two papers on this topic. The group was guided by interactions with Dr. Arlene Adviento-Borbe, USDA-ARS, Delta Water Resources Management Unit, Jonesboro, AR. Dr. Adviento-Borbe and Dr. Runkle discuss safety considerations, ethics of field research, and career options with each group member as part of their professional development training. Marguerita Leavitt, an M.S. student in the Runkle group, was responsible for analyzing eddy covariance methane flux data from 2020 in the context of other years of data. She has presented research at several virtual conferences and was awarded 2nd place in MS level poster competition at the Arkansas Soil and Water Conference in January 2021 and 4th place in 2022, and she was given a Top 5 Outstanding Student Presentation Award, at the North America Carbon Program Open Science Meeting (2021). Lena Abu-Ali, Ph.D. student in the Reid Lab, traveled to Arkansas in November 2021 to test equipment and methods for pore water sampling from the rice paddy fields that will be studied during the 2022 field season, and to return an intact soil block to the laboratory at Cornell for further testing to minimize impacts of iron oxidation on arsenic recovery. Pore water samplers that have been tested include several models from Soilmoisure Equipment Corp. with different surface areas of the porous ceramic sampler and Rhizon samplers from Rhizosphere Research Products. She presented her research at the SSSA meeting in Salt Lake City in November, 2021. She participated in ASA, CSSA, and SSSA Congressional Visit Days (virtually) in 2021. How have the results been disseminated to communities of interest?Results have been disseminated to scientists through presentations at the Soil Science Society of America and America Society of Agronomy meetings, the North American Carbon Program, and the Arkansas Soil and Water Conference which targeted USDA researchers, University researchers, farmers, and individuals in the Agronomic industry, as well as direct conversations with farmers. In addition, six publications have been accepted: Limmer, M.A., Seyfferth, A.L. Altering the localization and toxicity of arsenic in rice grain, Scientific Reports, 2022, In Press. Runkle BRK, Seyfferth AL, Reid MC, Limmer MA, Moreno-García B, Reavis CW, Pen?a J, Reba ML, Adviento-Borbe MAA, Pinson SRM, Isbell C, 2021. Socio-technical changes for sustainable rice production: rice husk amendment, conservation irrigation, and system changes, Frontiers in Agronomy, 3:741557, doi:10.3389/fagro.2021.741557, https://www.frontiersin.org/articles/10.3389/fagro.2021.741557/abstract. Limmer, M.A., Evans, A.E, Seyfferth, A.L. The IRIS Imager: A freeware program for quantification of paint removal on IRIS films. Soil Science Society of America Journal, 2021, 85, 2210-2219. Dykes, G.E., Limmer, M.A., Seyfferth, A.L. Silicon-rich soil amendments impact microbial community composition and the composition of arsM bearing microbes. Plant and Soil, 2021, 468, 147-164. Evans, A.E, Limmer, M.A., Seyfferth, A.L. Indicator of redox in soil (IRIS) films as a water management tool for rice farmers. Journal of Environmental Management, 2021, 294, 112920. Dykes, G.E., Chan, C., Seyfferth, A.L. 16S rRNA gene amplicon sequencing data from flooded rice paddy mesocosms treated with different silicon-rich soil amendments. Microbial Resource Announcements, 2021, 10, e0017821. What do you plan to do during the next reporting period to accomplish the goals?COVID-19 severely impacted the ability for our teams to conduct the husk-amendment field project in 2020 but we were able to amend fields at the end of the growing season in 2021. Therefore, the planned field sampling campaign will take place during the 2022 growing season. The team will meet via video conference in March 2022 to discuss logistics of the sampling plan. Seyfferth's group will continue with data analysis and manuscript preparation for the rice paddy mesocosm experiments. We will use two years of mesocosm study data to prepare manuscripts for publication. Seyfferth group will also partake in Arkansas field work by traveling to the field site in 2022 to collect samples, including soils and plants at harvest. Seyfferth group will perform plant analysis and soil analysis of these collected samples, including acid digestion and elemental analysis by ICP-MS to reveal As and Cd concentrations, plant nutrient contents, and As speciation Runkle's group will assess full-season GHG estimates from both field pairs after Si amendment using husk. In addition, supplemental information like measured field conditions, plant growth information (e.g., leaf area index) and farm operations information (e.g., rates and dates of chemical applications) will be recorded and reported. They will work with Dr. Arlene Adviento-Borbe, USDA-ARS, Delta Water Resources Management Unit, Jonesboro, AR to obtain gas flux data from chambers installed in each subplot in the field. Reid's group, including two Ph.D. students, will travel to the field site multiple times in 2022 to collect porewater samples for analysis. Two methods will be used: rhizon pore water samplers and spun-down soil cores. We will collect samples at least 4 times over the growing season and analyze them for pH, redox potential, total elemental concentration including As, Fe, Cd, and Si, speciation of As, and major anions and cations (SO42-, Ca2+, NH4+, etc.). We also plan to use anoxically-preserved pore water samples with a new anaerobic biosensor under development in the Reid Lab to determine how variations in solution chemistry affect As bioavailability to bacteria, which can be an important control on As methylation and demethylation rates.

Impacts
What was accomplished under these goals? After restricted field work in Arkansas due to the COVID-19 caused project delays, the team was finally able to meet in Arkansas in the fall of 2021 to amend paired fields with rice husk for the field experiment. A preliminary trip by members of the Seyfferth and Runkle groups took place just prior to harvest in 2021 where soils and plant samples were sampled and later analyzed for a variety of elements including Si and As. This preliminary trip sampled several fields to determine fields that appeared to be most deficient in plant available soil Si and would most benefit from husk addition, and also tested a soil spin-down method for sampling porewater.. Just after harvest, the full team met again in November 2021 at the field site. The Reid group tested porewater sampling devices both in the field and in the laboratory, and the whole team worked together to amend fields with rice husk at two different rates. These rates represent applying either 1 or 2 years of rice husk back into the field. We also included a subplot of chicken manure as requested by the farmer who allows us to work on his land. This chicken manure includes rice husk which is used as bedding in many AR chicken operations and thus could be an inexpensive source of plant available Si. In addition to the field work, Seyfferth's group is continuing to develop the UD Mesocosm study into a manuscript for publication, which is expected in 2022. This work combines 2 years of mesocosm data and statistical analysis has been completed, which has revealed the general observation that treatment of the rice straw (burned or unburned) had a significant effect on soil redox and silicon availability, resulting in higher plant As and methane emissions when unburned straw was incorporated into the rice paddies. Project M.S. student, M. Leavitt, is investigating drivers of methane fluxes in Field Pair 1, focus sites of a longer-term study. In particular, she is investigating flux dynamics during the ratoon crop, which grows a second harvest from the stubble left after the first one. Due to the fresh organic matter in the litter from the first crop, this period has significantly higher CH4 emissions that will inform the relationship between organic matter and greenhouse gas production, relevant to the addition of husk biomass that may unintentionally serve as a potential methanogenic substrate. Presentation of these initial works has been made at two virtual conferences during this reporting period: Leavitt M, Moreno Garcia B, Reavis CW, Reba ML, Runkle BRK, The Effect of Water Management and Ratoon Rice Cropping on Greenhouse Gas Emissions and Harvest Yield in Arkansas, Arkansas Soil and Water Conference, January 2022. Awarded 4th place in MS level poster competition Leavitt M, Moreno Garcia B, Reavis CW, Reba ML, Runkle BRK, The effect of ratoon rice cropping on greenhouse gas emissions and harvest yield in Arkansas, North America Carbon Program Meeting (virtual), March 2021 (Top 5 Outstanding Student Presentation Award) The main finding is that the greenhouse gas intensity of the ratoon crop is significantly higher than the main crop (7 to 40 times higher depending on the field and water management conditions). However, the ratoon period methane fluxes measured here were still one seventh of the only other ratoon CH4 emission study from the US. Further work in this cropping system is needed to provide a holistic assessment of its potential sustainability. Relevant to this project, Runkle's postdoc B. Moreno-García is analyzing metal(loid) content, including As and Cd, from grain sampled from a selection of rice farms under different management practices. These grains were analyzed in the Seyfferth lab for metal(loid) content in both bran and polished grain components. Initial results show that the ratoon-harvested rice has lower metal(loid) concentrations than the main crop season. These initial results have been presented at an international conference during this reporting period: Moreno-García, B., Limmer, M.A., Seyfferth, A.L., Reba, M., Runkle, B.R.K. Rice Grain Metal(loid) Concentration As Affected By Management Practices. Poster Presentation. ASA-CSSA-SSSA International Annual Meeting, Salt Lake City, Utah, US, November 7-10, 2021. Reid's team has focused on systematic field and laboratory evaluation of methods for sampling pore water from heavy clay soils and without being affected by formation of iron (oxy)hydroxide plaques in sample tubing, which had a significant impact on the ability to collect high quality data in the summer of 2019. Pore water was collected during the November 2021 trip from one of the fields planned for field work in 2022 and analyzed for a full suite of chemical parameters. A second field planned for field work in 2022 is a heavy clay soil, and laboratory work is underway to test methods for efficiently extracting pore water from this soil. In addition to in situ pore water samplers, the team plans to collect soil cores during the summer 2022 field season and store them under anoxic conditions in heat-sealed mylar bags prior to pore water extraction via centrifugation as another option for collecting pore water samples.

Publications

• Type: Journal Articles Status: Accepted Year Published: 2022 Citation: Limmer, M.A., Seyfferth, A.L. Altering the localization and toxicity of arsenic in rice grain, Scientific Reports, 2022, Accepted.
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Runkle BRK, Seyfferth AL, Reid MC, Limmer MA, Moreno-Garc�a B, Reavis CW, Pen?a J, Reba ML, Adviento-Borbe MAA, Pinson SRM, Isbell C, 2021. Socio-technical changes for sustainable rice production: rice husk amendment, conservation irrigation, and system changes, Frontiers in Agronomy, 3:741557, doi:10.3389/fagro.2021.741557, https://www.frontiersin.org/articles/10.3389/fagro.2021.741557/abstract.
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Dykes, G.E., Chan, C., Seyfferth, A.L. 16S rRNA gene amplicon sequencing data from flooded rice paddy mesocosms treated with different silicon-rich soil amendments. Microbial Resource Announcements, 2021, 10, e0017821.
• Type: Theses/Dissertations Status: Published Year Published: 2020 Citation: Evans, A.E. Using IRIS Films to inform alternate wetting and drying (AWD) water management in rice paddies. Thesis: University of Delaware
• Type: Theses/Dissertations Status: Published Year Published: 2021 Citation: Dykes, G.E. Soil microbial ecology and biogeochemical cycling of arsenic and iron in flooded rice paddies. Dissertation: University of Delaware
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Limmer, M.A., Evans, A.E, Seyfferth, A.L. The IRIS Imager: A freeware program for quantification of paint removal on IRIS films. Soil Science Society of America Journal, 2021, 85, 2210-2219.
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Dykes, G.E., Limmer, M.A., Seyfferth, A.L. Silicon-rich soil amendments impact microbial community composition and the composition of arsM bearing microbes. Plant and Soil, 2021, 468, 147-164.
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Evans, A.E, Limmer, M.A., Seyfferth, A.L. Indicator of redox in soil (IRIS) films as a water management tool for rice farmers. Journal of Environmental Management, 2021, 294, 112920.

Progress 03/15/20 to 03/14/21

Outputs
Target Audience:USDA researchers, University researchers, farmers, and individuals in the Agronomic industry. Changes/Problems:COVID-19 severely impacted the ability for our teams to conduct the husk-amendment field project in 2020. Unfortunately, the COVID-19 pandemic continues to pose health risks and it is unlikely that we will be able to perform husk amendments prior to the start of the field season in 2021. Therefore, the plan to execute the husk-amendment field project may again be delayed. Therefore, the one-year no-cost extention that we were recently granted may need to be extended for another year in order to perform the field experiment with husk addition. What opportunities for training and professional development has the project provided?Three graduate students, two undergraduate students, and one postdoc have been supported by this project. One additional postdoc and two graduate students have been working on this project but are supported by other funds. Abby Evans, M.S. student in the Seyfferth group, was primarily responsible for collecting and analyzing porewater chemistry, gas fluxes, and soil/Fe plaque during the growing season in the UD paddy mesocosms. Abby presented her work at the SSSA meeting in San Antonio in November, 2019, defended her thesis in May 2020, and submitted her manuscript that is currently under revision. A postdoc in the Seyfferth lab, Matt Limmer, trained the MS student and is primarily responsible for field maintenance, probe calibration, plant analysis, and data analysis. He has presented at conferences, published one paper on as a result of this work and has two additional manuscripts under various stages of preparation that will be submitted in 2021. Field work in Arkansas was delayed or reduced due to the COVID pandemic, as gas sampling campaigns and the husk addition treatment were impossible to perform safely. Some grain sampling, harvest yield estimates grain sample preparation, and bio-meteorological measurements in Field Pairs 1 and 2 were conducted by: Undergraduate hourly worker, Anthony Zadoorian, University of Arkansas, Biological Engineering Ph.D. student, Bennett Barr, University of Arkansas, Biological & Agricultural Engineering M.S. student, Marguerita Leavitt, University of Arkansas, Biological & Agricultural Engineering Ph.D. student, Colby Reavis, University of Arkansas, Biological & Agricultural Engineering Postdoctoral scientist, Beatriz Moreno-García, University of Arkansas, Biological & Agricultural Engineering The group was guided by interactions with Dr. Arlene Adviento-Borbe, USDA-ARS, Delta Water Resources Management Unit, Jonesboro, AR. Dr. Adviento-Borbe and Dr. Runkle discuss safety considerations, ethics of field research, and career options with each group member as part of their professional development training. Leavitt presented research at two virtual conferences in early 2021 and was awarded 2nd place in MS level poster competition at the Arkansas Soil and Water Conference in January 2021 Lena Abu-Ali, Ph.D. student in the Reid Lab, has been trained on HPLC-ICP-MS analysis of arsenic speciation in rice tissues and pore water, general instrumental methods for water quality analysis (e.g., ICP-MS; ion chromatography; total organic carbon analyzers), as well as the use of sensors to monitor soil physiochemical properties. She has developed and evaluated methods for sampling pore water from rice paddy fields that minimize impacts of iron oxidation on arsenic recovery. She presented her research at the SSSA meeting in San Antonio in November, 2019. She has participated in science communication workshops at Cornell University and received a Future Leaders in Science Award from the SSSA, through which she participated in ASA, CSSA, and SSSA Congressional Visit Days in 2020 and (virtually) in 2021. How have the results been disseminated to communities of interest?Results have been disseminated to scientists through presentations at the Soil Science Society of America meeting, the North American Carbon Program, the Arkansas Soil and Water Conference the Rice Technical Working Group which targeted USDA researchers, University researchers, farmers, and individuals in the Agronomic industry, as well as direct conversations with farmers. What do you plan to do during the next reporting period to accomplish the goals?COVID-19 severely impacted the ability for our teams to conduct the husk-amendment field project in 2020. Unfortunately, the COVID-19 pandemic continues to pose health risks and it is unlikely that we will be able to perform husk amendments prior to the start of the field season in 2021. Therefore, the plan to execute the husk-amendment field project may again be delayed. When it is safe to do so but likely near the end of the growing season in 2021, the larger teamwill meet in Arkansas to conduct field sampling and to prepare subplots for the husk-amendment study. We plan to amend field subplots with rice husk, which was the chosen amendment to increase Si in the paddy soils. Each group will plan to sample plots in Arkansas and perform other work as outlined below. Seyfferth's group will continue with data analysis and manuscript preparation for the rice paddy mesocosm experiments, including analysis of iron and manganese oxides at the Stanford Synchrotron Radiation Lightsource or NSLS-II. We will use two years of mesocosm study data to prepare manuscripts for publication. Seyfferth group will also partake in Arkansas field work by traveling to the field site in 2021 to amend soils, collect samples, and harvest plants. We will perform plant analysis and soil analysis of these collected samples, including acid digestion and elemental analysis by ICP-MS to reveal As and Cd concentrations, As speciation and preserve samples for microbial analyses. Runkle's group will assess full-season GHG estimates from both field pairs after Si amendment using husk. In addition, supplemental information like measured field conditions, plant growth information (e.g., leaf area index) and farm operations information (e.g., rates and dates of chemical applications) will be recorded and reported. They will work with Dr. Arlene Adviento-Borbe, USDA-ARS, Delta Water Resources Management Unit, Jonesboro, AR to obtain gas flux data from chambers installed in each subplot in the field. Reid's group will travel to the field site to further test and evaluate pore water sampling methods and to assist with preparation of sub-plots for the husk amendment study. In addition to pore water sampling methods (i) and (ii) outlined above, members of the Reid Lab will also collect soil cores using a push probe as an additional method for determining pore water solute concentrations. Soil cores will be stored in heat-sealed mylar bags with oxygen scrubbers. Bags will be opened in a Coy anaerobic chamber and core sections will be spun down in a centrifuge to collect pore water samples. In 2022, when the husk amendment experiment is planned to take place, Reid's group will spend an extended period of time in eastern Arkansas at the start of the growing season to assist with sensor installation and to ensure that field assistants are fully trained in the operation of all key instruments and equipment. This includes: (a) sampling procedure for porewater samplers; (b) installation and cleaning of Soilmoisture Equipment Corp samplers; (c) collection of soil cores and storage in heat-sealed mylar bags with oxygen scrubbers; (d) operation and calibration of a hand-held pH meter. Members of the Cornell team will also plan to return to Arkansas during at least two of the four scheduled samplings using pore water samplers and via the collection and anoxic preservation of soil cores.

Impacts
What was accomplished under these goals? In 2020, PI Seyfferth's group completed chemical analyses of the plants grown in the 18 rice paddy mesocosms (2 m2) at the University of Delaware. These paddies were operated under alternate wetting and drying for years 1 and 2 of the mesocosm study. Prior to planting, paddies were amended with rice straw or burned rice straw. Rice paddies were also amended with either rice husk, charred rice husk, or unamended as a control. Each paddy was planted with 49 rice plants (7 rows of 7). The porewater chemistry was sampled weekly using Rhizon samplers and measurements of pH, redox potential, colorimetric Si, colorimetric Fe, and colorimetric Mn have been completed. Results of elemental analysis of porewater via ICP-MS have been completed for both years, providing trace metal(loid) concentrations of Cd and As and also plant nutrients. Soil redox was measured continuously using in situ redox probes which were recorded at 15-minute intervals throughout the growing season. Greenhouse gas emissions were measured weekly using a chamber technique and data were processed in Matlab to obtain weekly methane fluxes throughout the growing seasons. Plants and soil were removed at 5 timepoints during the growing season to examine temporal trends in plant and soil chemistry. Rice was harvested 107 days after transplanting and yields averaged 2.7 kg per paddy (~200 bu/ac), with no treatment effect. Grain was been threshed, dehusked, polished, finely ground, and acid digested. Rice grain and bran were analyzed for total elemental composition and also extracted for As speciation analysis by LC-ICP-MS. Rice roots were extracted with a dithionite-citrate-bicarbonate extraction to assess the concentration of As, Fe, Mn, and Si in the root iron plaque. Root plaques have also been analyzed at either the Stanford Synchrotron Radiation Lightsource (SSRL) or the National Synchrotron Light Source (NSLS-II) to determine the iron mineral composition and arsenic speciation in the root plaque. Additional plant parts, including flag leaves, straw, and nodes have been ground, acid digested, and analyzed for total elemental composition. The data from years 1 and 2 have been combined and statistical analysis has been largely completed, which has revealed the general observation that treatment of the rice straw (burned or unburned) had a significant effect on soil redox and silicon availability, resulting in higher plant As and methane emissions when unburned straw was incorporated into the rice paddies. These data will be put into a manuscript this year. All PIs and students and postdocs working on this project met via video-conference in March 2020 and 2021 to discuss plans for the next review period. The Arkansas-based team had several discussions with the collaborating farmers in March, 2020, to discuss project plans. Some logistical details about husk acquisition and incorporation, experimental design, and expected work-plan were created, but ultimately delayed to 2021 or 2022 due to the COVID pandemic. A new project M.S. student, M. Leavitt, started in June, 2020. Her thesis research project will help determine drivers of methane fluxes in Field Pair 1, focus sites of a longer-term study. In particular, she is investigating flux dynamics during the ratoon crop, which grows a second harvest from the stubble left after the first one. Due to the fresh organic matter in the litter from the first crop, this period has significantly higher CH4 emissions that will inform the relationship between organic matter and greenhouse gas production, relevant to the addition of husk biomass that may unintentionally serve as a potential methanogenic substrate. Presentation of these initial works has been made at two virtual conferences in early 2021: Leavitt M, Moreno Garcia B, Reavis CW, Reba ML, Runkle BRK, The effect of ratoon rice cropping on greenhouse gas emissions and harvest yield in Arkansas, Arkansas Soil and Water Conference, January 2021. Awarded 2nd place in MS level poster competition Leavitt M, Moreno Garcia B, Reavis CW, Reba ML, Runkle BRK, The effect of ratoon rice cropping on greenhouse gas emissions and harvest yield in Arkansas, North America Carbon Program Meeting (virtual), March 2021 The main finding is that the greenhouse gas intensity of the ratoon crop is significantly higher than the main crop (7 to 40 times higher depending on the field and water management conditions). However, the ratoon period methane fluxes measured here were still one seventh of the only other ratoon CH4 emission study from the US. Further work in this cropping system is needed to provide a holistic assessment of its potential sustainability. Relevant to this project, Runkle's postdoc B. Moreno-García is analyzing metal(loid) content, including As and Cd, from grain sampled from a selection of rice farms under different management practices. These grains were analyzed in the Seyfferth lab for metal(loid) content in both bran and polished grain components. In 2020, Reid's team focused on systematic laboratory evaluation of methods for sampling pore water without being affected by formation of iron (oxy)hydroxide plaques in sample tubing, which had a significant impact on the ability to collect high quality data in the summer of 2019. This focus on laboratory work was necessitated by the inability to travel to field sites in eastern Arkansas in the summer of 2020. Two sampling methods were tested using an intact block (roughly 40 cm x 40 xm x 40 cm) of paddy soil shipped from Arkansas and maintained under flooded conditions in a container, and in flooded soil microcosms: Rhizon porewater samplers (Rhizosphere Research Products, Netherlands) semi-permanently installed in the soil. Porewater samplers from Soilmoisture Equipment Corp. These samplers have a rigid body which allows them to be inserted from the surface to the target depths. The plan for the husk amendment study, to be performed in 2022, is that these samplers will be used at four time points during the growing season to collect porewater samples. After sample collection, they will be removed, cleaned with dithionite and/or ammonium oxalate (pH 3) to remove iron plaques, rinsed with distilled water, and then used for the next sampling. The timing of these samples will be coordinated with key physiological growth stages of the rice. It was determined that the rhizon samplers can underestimate dissolved As concentrations by 10-50% if there is significant iron plaque in the tubing. Iron plaque formed after 3-4 weeks of soil saturation, corresponding to strongly Fe-reducing conditions in the soil, so rhizon samplers may still provide useful information about the early stage of soil flooding. Option (ii) was shown to produce higher quality pore water data, as long as the Soilmoisture samplers were installed at least 24 hours prior to sampling so that the effects of the disturbance were minimized.

Publications

• Type: Journal Articles Status: Under Review Year Published: 2021 Citation: Evans, A., Limmer, M.A., Seyfferth, A.L. Indicator of Redox in Soil (IRIS) Films as a Water Management Tool for Rice Farmers. Journal of Environmental Management. In Revision.
• Type: Journal Articles Status: Other Year Published: 2021 Citation: Runkle, B., Seyfferth, A.L., Reid, M.R., Limmer, M.A. et al. Perspective on co-implementing rice husk amendment and alternate wetting and drying irrigation for sustainable rice production. In preparation
• Type: Theses/Dissertations Status: Published Year Published: 2020 Citation: Evans, A. E. USING IRIS FILMS TO INFORM ALTERNATE WETTING AND DRYING (AWD) WATER MANAGEMENT IN RICE PADDIES. Thesis: University of Delaware.

Progress 03/15/19 to 03/14/20

Outputs
Target Audience:Farmers and scientists Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Three graduate students, two undergraduate students, and one postdoc have been supported by this project. One additional postdoc and graduate student have been working on this project but are supported by other funds. Abby Evans, M.S. student in the Seyfferth group, has been trained on porewater and gas fluxing techniques and was primarily responsible for collecting and analyzing porewater chemistry, gas fluxes, and soil/Fe plaque during the growing season in the UD paddy mesocosms. Abby presented her work at the SSSA meeting in San Antonio in November, 2019. A postdoc in the Seyfferth lab, Matt Limmer, has trained the student and is primarily responsible for field maintenance, probe calibration, and plant analysis. Chamber measurements in Field Pairs 1 and 2 were conducted by: Undergraduate hourly workers, Anthony Zadoorian and Juan Arguilo, University of Arkansas, Biological Engineering Ph.D. student, Bennett Barr, University of Arkansas, Biological & Agricultural Engineering Ph.D. student, Colby Reavis, University of Arkansas, Biological & Agricultural Engineering Postdoctoral scientist, Beatriz Moreno-García, University of Arkansas, Biological & Agricultural Engineering The group was guided by interactions with Dr. Arlene Adviento-Borbe, USDA-ARS, Delta Water Resources Management Unit, Jonesboro, AR. Dr. Adviento-Borbe and Dr. Runkle discuss safety considerations, ethics of field research, and career options with each group member as part of their professional development training. Porewater measurements in Field Pairs 1 and 2 were conducted by Lena Abu-Ali, Ph.D. student in the Reid group at Cornell University with field assistance from Anthony Zadoorian from U Arkansas. How have the results been disseminated to communities of interest?Results have been disseminated to scientists through presentations at the Soil Science Society of America meeting and to the farmers via personal conversations. We plan to present results at the Rice Technical Working Group conference in February 2020, which will target USDA researchers, University researchers, farmers, and individuals in the Agronomic industry. What do you plan to do during the next reporting period to accomplish the goals?In Project Year 3, all PIs will meet in Arkansas in at the beginning of the 2020 growing season to amend field subplots with rice husk, which was the chosen amendment to increase Si in the paddy soils. Each group will plan to sample plots in Arkansas and perform other work as outlined below. Seyfferth's group will continue processing rice paddy microcosm samples, including acid digestion and elemental analysis by ICP-MS to reveal As and Cd concentrations. We will also perform grain As speciation using HPLC-ICP-MS. Root plaques will also be analyzed at the Stanford Synchrotron Radiation Lightsource for iron mineral composition. With a complete dataset of two years of mesocosm study, statistical analyses and manuscript writing will commence. We will also partake in Arkansas field work by traveling to the field site to amend soils, collect samples, and harvest plants. We will perform plant analysis and soil analysis of these collected samples, including speciation and microbial analyses. Runkle's group will assess full-season GHG estimates from both field pairs after Si amendment using husk. In addition, supplemental information like measured field conditions, plant growth information (e.g., leaf area index) and farm operations information (e.g., rates and dates of chemical applications) will be recorded and reported. They will work with Dr. Arlene Adviento-Borbe, USDA-ARS, Delta Water Resources Management Unit, Jonesboro, AR to obtain gas flux data from chambers installed in each subplot in the field. Reid's group will monitor the porewater chemistry in field trials in Arkansas in the summer of 2020. They plan to use three types of porewater samplers to add redundancy to our porewater sampling plan: Rhizon porewater samplers (Rhizosphere Research Products, Netherlands) semi-permanently installed in the soil at depths of 10 and 25 cm and sampled once every two weeks. Porewater samplers from Soilmoisture Equipment Corp. These samplers have a rigid body which allows them to be inserted from the surface to the target depths. These samplers will be used at four points during the growing season to collect porewater samples. After sample collection, they will be removed, cleaned with dithionite to remove iron plaques, rinsed with distilled water, and then used for the next sampling. The timing of these samples will be coordinated with key physiological growth stages of the rice. Soil cores will be collected to a depth of 25 cm, stored in heat-sealed Mylar bags with a Mitsubishi oxygen absorber, and stored at 4°C. Collection of soil cores will occur four times in the growing season and will be coordinated with key physiological growth stages of the rice. If there are significant problems with methods (i) and (ii), cores will be sectioned inside a Coy anaerobic chamber. Core sections from 10 and 25 cm will be centrifuged and the supernatant will be collected and analyzed for porewater chemical parameters. Soil cores will also be used to collect samples for later biomolecular analysis of arsM abundance and expression, pending the availability of personnel to perform this work. In addition, members of the Cornell team will spend an extended period of time in eastern Arkansas at the start of the growing season to ensure that field assistants are fully trained in the operation of all key instruments and equipment. This includes: (i) sampling procedure for porewater samplers; (ii) installation and cleaning of Soilmoisture Equipment Corp samplers; (iii) collection of soil cores and storage in heat-sealed mylar bags with oxygen scrubbers; (iv) operation and calibration of a hand-held pH meter. Members of the Cornell team will also plan to return to Arkansas during at least two of the four scheduled samplings with methods ii and iii.

Impacts
What was accomplished under these goals? All PIs and students and postdocs working on this project met in Arkansas in March 2019 to discuss plans for the next year. There, we met with the farmers who allowed us to use their land for experimentation, and we toured and met with individuals from Riceland Mills, who have agreed to donate rice hulls for soil amendment for this project. The PIs and students also discussed our plan for the fieldwork in Arkansas, and the Seyfferth group continued to perform rice experiments in the UD mesocosms, as outlined below. In 2019, PI Seyfferth's group grew rice in 18 rice paddy microcosms (2 m2) at the University of Delaware under alternate wetting and drying, which represents year 2 of the mesocosm study. Prior to planting, paddies were amended with rice straw or burned rice straw. Rice paddies were also amended with either rice husk, charred rice husk, or unamended as a control. Each paddy was planted with 49 rice plants (7 rows of 7). The porewater chemistry was sampled weekly using Rhizon samplers and measurements of pH, redox potential, colorimetric Si, colorimetric Fe, and colorimetric Mn have been completed. Results of elemental analysis of porewater via ICP-MS are currently pending, which will provide trace metal(loid) concentrations of Cd and As. Soil redox was measured continuously using in situ redox probes which were recorded at 15-minute intervals throughout the growing season. Greenhouse gas emissions were measured weekly using a chamber technique and preliminary analysis has been performed. Plants and soil were removed at 5 timepoints during the growing season to examine temporal trends in plant and soil chemistry. Rice was harvested 107 days after transplanting and yields averaged 2 kg per paddy, with no treatment effect. Grain has been threshed, dehusked, polished, and finely ground for acid digestion. Rice roots have been extracted with a dithionite-citrate-bicarbonate extraction to assess the concentration of As, Fe, Mn, and Si in the root iron plaque. Root plaques have also been analyzed at the Stanford Synchrotron Radiation Lightsource for arsenic spectroscopy. Additional plant parts being processed include flag leaves, straw, and nodes. In addition, we have completed all of the analyses for the 2018 growing season and are working toward putting that data into a manuscript for publication. Co-PI Runkle's group again tested GHG fluxes in field pairs to be used in the project field trials. Field Pair 1, in study since 2014, was given "AWD" irrigation management. Field Pair 2, the pair to be silica-amended during the 2020 season, was given "continuous flood" and "AWD" irrigation management. In Field Pair 2 both fields were mostly in AWD and one of the fields experienced a full dry-down in early August. However, that field was reflooded the next day because of rain and concerns for plant stress, and the other field never experienced a full dry down due to rain. Pair 1 received both eddy covariance and weekly season-long closed chamber observations of greenhouse gas (GHG) emissions. Pair 2 received season-long closed chamber observations of GHG emissions as well as porewater sampling and monitoring. Instruments for monitoring were installed in Field Pair 1 and closed chamber monitoring began after the fields were planted on May 13th. Due to rain, Field Pair 2 was not planted until June 4th and June 10th respectively, so closed chamber monitoring was delayed until early June. The irrigation treatments and greenhouse gas measurements were achieved as required for Field Pairs 1 and 2. By the chamber technique, the seasonal CH4 emissions for Field Pair 1 were 18 ± 3 and 72 ± 7.6 kg CH4-C/ha/season, and the emissions for Field Pair 2 were 304 ± 16 and 186 ± 18 kg CH4-C/ha/season. N2O emissions for Field Pair 1 were 0.28 ± 0.03 and 0.24 ± 0.06 kg N2O-N/ha/season, and for Field Pair 2 they were -0.01 ± 0.03 and 0.48 ± 0.07 kg N2O-N/ha/season. These seasonal emissions were calculated from 13 sets of chamber measurements completed for Field Pair 1 between June 18th and September 6th. Field Pair 2's emissions were calculated from 15 sets of chamber measurements for one field and 13 for the other (there were two days where measurements could not be taken due to spraying in the fields) taken between July 2nd and September 27th. Field emissions in Field Pair 1 were higher than the AWD field in 2018, which produced seasonal emissions of 1.17 kg CH4-C/ha/season. Field Pair 1 was harvested on September 12th, and samples were taken of plants, the soil, and rice from the combine for analysis. Similar samples were taken for Field Pair 2, which was harvested on October 10th for one field and the end of October for the other. Yield data has not yet been received as samples are still being processed. Several manuscripts have been outlined. The Cornell team pursued three objectives in the 2019 summer field season: Monitor physiochemical properties in Baker 30 (B30) and Baker 50 (B50) Monitor greenhouse gases (CH4 and N2O) in soil in B30 and B50 rice paddy soils Monitor porewater chemistry in B30 and B50 rice paddy soils Objective 1: Volumetric water content (VWC) sensors (Campbell Scientific CS655) were inserted horizontally into the soil at depths of 10 and 25 cm from a trench. Redox probes (Paleo Terra, Amsterdam, Netherlands) with platinum electrodes at 0, 10, 18, and 25 cm depths were installed in three locations in each field, within ~1 m of the VWC sensors and porewater samplers. Ag AgCl KCl reference electrodes were mounted in screened PVC wells located nearby. Sensors were connected to a Campbell Scientific CR1000X Datalogger and data were recorded at 30 minute intervals. Objective 2: Porewater samplers (Soilmoisture Equipment Corp) were inserted at depths of 10 cm (shallow) ad 25 cm (deep). Porewater samples were collected using pre-evacuated, crimp-sealed glass serum vials with blue stoppers. All vials were acid washed and triple-rinsed with ultrapure water prior to use. Prior to sample collection, a three-way polycarbonate luer stopcock was connected to the rhizon sampler. A 50 mL locking syringe was used to void the dead volume, and then the stopcock position was switched to divert the water from the sampler into the serum vial. Due to low flow rates through the sampler, presumably due to the high clay content and low permeability of the soils, vials were left for one to three days to collect porewater. The headspace of the serum vials was sampled for analysis of CH4 and N2O concentrations on a Shimadzu GC-2014. CH4 was measured with a flame ionization detector and N2O was measured with an electron capture detector. We noted that almost all vials retained some vacuum, so ultra high purity N2 was added to the vial headspace prior to sampling. Based on the volume of water collected and volume of N2 added to offset the residual vacuum, we calculated the volume of pore gas that had collected in the vials. Because both pore water and pore gas were collected in the vials, we report N2O and CH4 concentrations in both pore gas and pore water. The calculation is based on the assumption that the pore gas and pore water were in equilibrium in the subsurface. N2O concentrations were at or below the level of quantification in most samples. Objective 3: Selected solid-phase elemental concentrations from B30 and B50 are provided in Table 1. Porewater samples were collected from serum vials after the vial headspace was sampled for gases, and were diluted in 2% trace metal grade nitric acid analyzed via ICP-MS (Agilent 7800) operating with a helium reaction cell for total Si, Fe, Mn, and As. Major anions (SO42-, NO3-) and cations (Ca2+, Mg2+) were measured with anion and cation exchange ion chromatography (Dionex ICS-2100). A relatively small subset of samples were measured for major cations.

Publications

Progress 03/15/18 to 03/14/19

Outputs
Target Audience:The target audience has included colleages at the AGU and SSSA meetings during research presentations as well as one-on-one conversations with the farmer who has alowed field access for field trials. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?One graduate student, one postdoc and one undergraduate student have been supported by this project. Two other graduate students and one postdoc have been working on this project but are supported by other funds. Abby Evans, M.S. student in the Seyfferth group, has been trained on porewater and gas fluxing techniques and was primarily responsible for collecting and analyzing porewater chemistry, gas fluxes, and soil/Fe plaque during the growing season. Abby presented her work at the SSSA meeting in San Diego in January, 2019. A postdoc in the Seyfferth lab, Matt Limmer, has trained the student and is primarily responsible for field maintenance, probe calibration, and plant analysis. Chamber measurements in Field Pair 2 were conducted by: Undergraduate hourly worker, Micaela Wine, Arkansas State University, Biology Ph.D. student, Colby Reavis, University of Arkansas, Biological & Agricultural Engineering Postdoctoral scientist, Beatriz Moreno-García, University of Arkansas, Biological & Agricultural Engineering The group was guided by interactions with Dr. Arlene Adviento-Borbe, USDA-ARS, Delta Water Resources Management Unit, Jonesboro, AR. Dr. Adviento-Borbe and Dr. Runkle discuss safety considerations, ethics of field research, and career options with each group member as part of their professional development training. A graduate student has been recruited to start work in June, 2019. Bennett Barr, who has a B.S.M.E. in Mechanical Engineering from the University of Mississippi (BS GPA of 3.81; Magna cum Laude) and an M.S. degree from the Department of Agricultural and Biosystems Engineering at Iowa State University (expected May, 2019; current GPA 3.75). Her achievements have been recognized by the University of Arkansas Graduate School, who has offered her a prestigious Distinguished Doctoral Scholarship (one of approx. 25 awarded per year) to support her graduate studies. How have the results been disseminated to communities of interest?Abby Evans presented her work at the SSSA meeting in January 2019. Runkle's group members presented their work at the AGU conference in Washington, DC in Decemer 2018. What do you plan to do during the next reporting period to accomplish the goals?In Project Year 2, all PIs will meet in Arkansas in March 2019 to discuss research findings from Project Year 1 and plan for the upcoming year. We will also meet with the farmer who has allowed us to conduct the research on his fields, and visit Riceland Mills to have a tour and discuss the feasibility of obtaining large amounts of Si rich materials from them (husk and charred husk). Seyfferth's group will continue processing rice paddy microcosm samples, including acid digestion and elemental analysis by ICP-MS to reveal As and Cd concentrations. We will also perform grain As speciation using HPLC-ICP-MS. Root plaques will also be analyzed at the Stanford Synchrotron Radiation Lightsource for iron mineral composition. With a complete dataset, statistical analyses and manuscript writing will commence. Rice will be grown in the rice paddy microcosms for a second field season following a similar schedule and protocol. Reid's group will monitor the porewater chemistry and microbial community changes in field trials in Arkansas in the summer of 2019. Two fields will be amended with straw and husk (i.e., Si) treatments informed by mesocosm results and similar methods will be used as in the mesocosms to collect porewater and soil chemistry data along with plant samples for analysis. PI Reid's group will also measure volatile arsine species in the field trials in the summer of 2019 to determine the contribution of biovolatilization to arsenic mass balances in paddy fields amended with different sources of silicon. Runkle's group will assess full-season GHG estimates from both field pairs. In addition, supplemental information like measured field conditions, plant growth information (e.g., leaf area index) and farm operations information (e.g., rates and dates of chemical applications) will be recorded and reported.

Impacts
What was accomplished under these goals? This past year, PI Seyfferth's group grew rice in 18 rice paddy microcosms (2 m2) at the University of Delaware under alternate wetting and drying. Prior to planting, paddies were amended with rice straw or burned rice straw. Rice paddies were also amended with either rice husk, charred rice husk, or unamended as a control. Each paddy was planted with 49 rice plants (7 rows of 7). The porewater chemistry was sampled weekly using Rhizon samplers and measurements of pH, redox potential, colorimetric Si, colorimetric Fe, and colorimetric Mn have been completed. Results of elemental analysis of porewater via ICP-MS are currently pending, which will provide trace metal(loid) concentrations of Cd and As. Soil redox was measured continuously using in situ redox probes which were recorded at 15-minute intervals throughout the growing season. Greenhouse gas emissions were measured weekly using a chamber technique and preliminary analysis has been performed. Plants and soil were removed at 5 timepoints during the growing season to examine temporal trends in plant and soil chemistry. Rice was harvested 107 days after transplanting and yields averaged 2 kg per paddy, with no treatment effect. Grain has been threshed, dehusked, polished, and finely ground for acid digestion. Rice roots have been extracted with a dithionite-citrate-bicarbonate extraction to assess the concentration of As, Fe, Mn, and Si in the root iron plaque. Root plaques have also been analyzed at the Stanford Synchrotron Radiation Lightsource for arsenic spectroscopy. Additional plant parts being processed include flag leaves, straw, and nodes. Co-PI Runkle's group identified and tested GHG fluxes in field pairs to be used in the project field trials. Field Pair 1, in study since 2014, was given "continuous flood" and "AWD" irrigation management, following the grant protocol. Field Pair 2, expected to be the experimental treatment pair in Years 2 and 3, was given continuous flood conditions, also per the grant protocol. Pair 1 received both eddy covariance and season-long closed chamber observations of greenhouse gas (GHG) emissions. Pair 2 received a two week, mid-summer, short campaign of closed chamber observations to detail its baseline GHG production potential. Field Pair 2 was selected - the fields are adjacent to each other and across a field road from Field Pair 1, so offer near-identical meteorological conditions and similar soil conditions. They have a similar cultivation history and like Field Pair 1, they have been zero-graded to have 0% slope. Instruments for Field Pair 2 have been purchased, delivered, and tested, and are ready for installation immediately after planting in April or May, 2019. We achieved field irrigation treatments as required and conducted greenhouse gas measurements as indicated above. By the chamber technique, the CH4 emissions of the AWD treatment were very low (less than 200 g CH4-C ha-1 d-1 in every measurement interval) while the emissions of the flooded field were substantial (reaching 1200 g CH4-C ha-1 d-1, which, while high, is much less than the peak recorded in 2017 of 5000 g CH4-C ha-1 d-1). In Field pair 2, measurements were taken 8-Aug and 14-Aug and the values ranged from 344 to 1800 g CH4-C ha-1 d-1. Thus in Field pair 2, the methane emissions potential is similar to the longer-term study sites in Field Pair 1. Further attention to differences between the fields (e.g., in soil organic content or bulk density) will be investigated in the coming two years. Co-PI Reid's group gained experience in deploying a distributed sensor network and in the sampling and analysis of porewater from Arkansas paddy soils managed under alternate wetting and drying. These approaches are now field-tested and ready for use in the summer of 2019. In addition, Reid's group also performed laboratory development of chemotrapping methods for measuring arsine volatilization fluxes from paddy soils, which will be field-tested in the summer of 2019. All PIs meet to discuss plans during the AGU conference in Washington, DC in December 2018.

Publications