Research Project: Managing Nutrient, Carbon, and Water Fluxes to Provide Sustainable and Resilient Cropping Systems for Midwestern Landscapes

Location: Agroecosystems Management Research

2025 Annual Report

Objectives
Objective 1: Develop climate-smart frameworks for providing actionable information on both conventional and aspirational corn- and soybean-based cropping systems, including organic systems, with foci on nutrient cycling, soil water dynamics, and indicators of soil health. Sub-Objective 1.A: Determine effects of conventional and aspirational C-S based cropping systems, including organic systems, on soil nutrient dynamics, nutrient losses in subsurface drainage, crop nutrient uptake, and crop yield with a vision for developing climate resilient cropping systems for regional producers. Sub-Objective 1.B: Determine effects of conventional and aspirational C-S based cropping systems, including organic systems, on indicators of soil health. Objective 2: Provide actionable information on the influence of microclimates modified by conservation management practices (such as no-till, relay or double cropping, extended rotations) on production efficiency and resilience of corn-soybean, organic, agroforestry, and forage-based cropping systems. Sub-Objective 2.A: Quantify differences in soil temperature, plant available water, and canopy microclimate between conventional and aspirational row-crop systems and forage-based systems that impact sustainability and productivity outcomes. Sub-Objective 2.B: Utilize measurements of light interception and weather data to compare RUE and PUE between conventional and aspirational row-crop systems and forage-based systems.

Approach
A combination of controlled experiments in the field and laboratory, tile drainage monitoring, and a variety of modeling techniques and statistical analyses will quantify the effects of 4R management (Right source, Right rate, Right time, and Right place) of nitrogen on nutrient (nitrogen, phosphorus, potassium, and sulfur) cycling in a corn-soybean system (Objective 1). This same approach will be used to determine the ability of cover crops and double-cropping to reduce nitrate losses and maintain soil health in a corn-soybean system, and the efficacy of an organic cropping system with extended rotations to both reduce nitrate losses and enhance soil health. We will determine how fall-planted cover crops and no-tillage within prevailing and alternative corn-soybean rotations affect tile drainage water flow and nutrient concentrations, and how drainage water quality and soil profile water storage differ in organic systems compared with prevailing corn-soybean systems. We will also quantify how diversified systemwide management affects water- and light-use efficiency of row crops and pastures (Objective 2). The approaches we have used in corn-soybean systems will be applied to pasture systems to provide quantitative assessments of the value of silvopasture systems in the Midwest. We will use several indicators of soil health, such as aggregate stability and nitrogen mineralization potential, to compare and contrast prevailing corn-soybean based cropping systems, corn-soybean based systems that include cover crops and double crops, and organic systems that include extended rotations. These comparisons are being conducted via experimental plots with individual subsurface (tile) drains that allow robust measurements of hydrologic and nutrient balances. We are monitoring microclimate (e.g., wind speed and evaporation) in long-term plots to understand the effectiveness of silvopasture systems as a climate change adaptation strategy that may reduce either the severity of extreme events (e.g., drought) or the impact of annual or seasonal climate trends (e.g., increasing temperature). Through a well-designed series of experiments that support modeling and upscaling and by employing the LTAR infrastructure, this study will identify optimal combinations of climate-smart practices and aspirational cropping systems that increase production and offset detrimental impacts to the environment.

Progress Report
Objective 1: The Long-Term Agroecosystem Research (LTAR) Common Experiment established at the Iowa State University Kelley Research Farm located near Ames, Iowa, continued in 2024 and 2025. Established treatments at the Kelley Farm Drainage Plots (KFDP) contrast different nitrogen (N) management strategies, and include measurements of nutrient losses (N, phosphorus (P), potassium (K), and sulfur (S)) in tile drainage. The experiment compares a prevailing (conventional) corn-soybean (C-S) cropping system with tillage and fixed N fertilizer applications to four alternative C-S systems: 1) no-till C-S; 2) no-till C-S with a cereal rye winter cover crop; 3) no-till C-S with a fertilized winter cereal rye biomass crop that is double cropped with a soybean crop; and 4) a system with a winter covercress crop following corn that is double cropped with a subsequent soybean crop. When corn is grown in even years, each of these alternative systems uses the late-spring nitrate test to determine spring sidedress N application rates. In 2024, the corn crop was harvested, and above-ground biomass and nutrient content measurements were made, as were nutrient contents for the grain. Similar research efforts are ongoing for the 2025 covercress and soybean crops, with planned measurements of above-ground biomass and nutrient content as well as nutrient contents for the covercress oilseed and soybean grain. Key soil health metrics including wet aggregate stability, organic carbon content, pH, extractable P and K, and potentially mineralizable N were also measured. Data from the Kelley Farm Drainage Plots have been deposited in an internal database at the National Laboratory for Agriculture and the Environment (NLAE). As available, these data are being exported to ARS databases. Established treatments at the Organic Water Quality (OWQ) research site located near Ames, Iowa, contrast a prevailing C-S system with an organic corn-soybean-oat-alfalfa-alfalfa-alfalfa system, using replicated tile-drained plots. In 2024, yield data were collected but have yet to be summarized. Similarly, assessment of key soil health indicators and data on nitrate-N loss in tile drainage from these systems collected during 2024 are still being processed. Research efforts are ongoing for the 2025 crop. Weekly soil temperature measurements were added in 2025. Each year, data from the OWQ research site have been stored in an internal database at NLAE. Objective 2: During 2024 and 2025, the effects of diversified systemwide management on water- and light-use efficiency of row crops and pastures were evaluated. Soil temperature and water content were measured in select plots beginning in the fall of 2024 at the KFDP, and the effort was expanded in the spring of 2025 after acquiring additional soil water and temperature profile sensors. The plots at this site are not yet equipped with sensors for continuous monitoring of soil surface and plant canopy temperature. At the Arkansas silvopasture research site soil temperature and water content, soil surface temperature, and plant canopy temperatures were all measured throughout the growing season. The forage understory at the Arkansas silvopasture site is in the process of being reestablished. The site was managed for invasive species throughout 2024, and it was tilled and reseeded in the spring of 2025. Calculating radiation-use efficiency (RUE) and precipitation-use efficiency (PUE) was not possible due to the re-establishment. Measurements of incoming radiation and precipitation are also underway at KFDP, and the crop biomass will be sampled in 2025 to calculate RUE and PUE. These efforts support the project goal of developing actionable data on the influence of local weather modified by conservation management practices (such as no-till, relay or double cropping, extended rotations) on production efficiency and resilience of C-S, organic, agroforestry, and forage-based cropping systems). Field monitoring of surface energy, moisture, and carbon dioxide fluxes via eddy covariance (EC) are continuing at the LTAR field sites, along with local meteorological measurements, as a part of a long-term study at a corn/soybean rotation production field under reduced tillage near Williams, Iowa. Also, a chamber monitoring system was tested at the site in 2024 and redeployed in 2025 to capture the spatial variability of nitrous oxide (N2O) and other emissions altering nutrient availability at the site. These data not only expand the suite of measurements available at this LTAR site, but also are the basis for a study to understand the effects of reduced tillage production systems on crop yields and nutrient losses. Efforts also continued to develop a robust measurement and data-processing protocol for using the Los Gatos Research (LGR) gas analyzer to monitor N2O losses at the site via EC. This would allow long-term, area-integrated measurements of N2O to be monitored at the site. New software for the gas analyzer was developed to reduce the time jitter of the LGR sensor, improve the synchronicity LGR sensor with a sonic anemometer, and enhance the data quality. This significantly improved direct measurements of N2O fluxes at the field site and measurements will continue throughout the year to characterize temporal variability in N2O losses with respect to rainfall and diurnal soil temperatures. Work in California on the GRAPEX (Grape Remote sensing Atmospheric Profile & Evapotranspiration eXperiment) project design has expanded to include new vineyards in the Finger Lakes region of upstate New York. This work builds off the successes of GRAPEx in California in increasing water use efficiency to include a region of U.S. grape production that has considerably different weather conditions (more humidity) which increases fungal infections in wine grapes. Similar to grape production systems in California, canopy vine structure influences exchange and transport processes of water vapor and carbon dioxide that pass through the canopy via ventilation shafts produced by vine branches and leaves. A new design of vine trellising with synchronized high-frequency eddy covariance (EC) measurements for below/within vine canopies has been developed and deployed in the New York vineyards. Three eddy covariance systems were deployed in a production vineyard near Geneva, New York, in May 2025. For the GRAPEx project, new digital signal processing algorithms for high frequency data below/within vine canopies are being developed. Improved understanding of the vertical motions of air through a canopy in structured agricultural canopies will improve remote sensing modeling of evapotranspiration for vineyards and other agricultural systems.

Accomplishments
1. Sulfur fertilizer improves sulfur nutrition of corn but rarely increases grain yield. Sulfur (S) is an essential plant nutrient that must be available to corn roots for optimum plant growth, but the benefits of S fertilizer for corn production in Iowa are uncertain. ARS scientists in Ames, Iowa, and Iowa State University colleagues carried out a field study to evaluate the performance of three types of S fertilizers for corn grown during 12 consecutive years in highly productive central Iowa soils. We found that S fertilizer increased S uptake by the corn plants, especially in the early part of the growing season, but increased corn grain yield in only 2 of 12 (17%) study years. Measures of soil and plant tissue S failed as predictors of grain response to S fertilizer. Economic return from S fertilizer application was positive at current price levels (average return up to $ 11.17 per acre) when we accounted for the value of nitrogen in the fertilizer materials. Overall, our results showed that S application may improve early season S uptake by the corn plant but rarely increases grain yield. However, long-term positive economic returns are still possible. The results of this research benefit both commercial growers and the fertilizer industry by providing nutrient management guidelines that maximize crop utilization and yields.

2. Organic cropping systems enhance soil health indicators in a Mollisol of the U.S. Corn Belt. Organic farming may sustain soil health compared with conventional farming due to the practices embedded within the system itself. Studies comparing organic farming with conventional row-crop farming in the long term are few. ARS scientists in Ames, Iowa, compared the impacts of conventional and organic cropping systems on soil health indicators. The experiment was managed under these cropping systems for 9 years and took place on highly fertile central Iowa soil. The conventional system was corn and soybean rotation. The organic system was corn, soybean, oat/alfalfa, and alfalfa rotation. The conventional and organic rotations were also compared with an organic perennial pasture. Results showed that organic systems improved soil microbial biomass and activity, easily degraded soil organic matter, and improved soil structure compared with the conventional system. However, organic systems did not generally improve soil carbon content, total nitrogen (N) content, pH, electrical conductivity, and concentrations of inorganic N, phosphorus and potassium. They had varying effects on soil fertility indicators. The use of perennial crops, animal manure, reduced tillage frequency, and increased plant inputs in the organic systems contributed to improvement in these soil health indicators. Overall organic systems improved soil health indicators but had minimal effects on soil fertility indicators in this highly fertile soil, which is in agreement with what organic farmers have observed. These findings enhance the understanding of organic farming by farmers, policymakers, and the scientific community and its impacts on soil health in fertile soils.

3. Benefits of cover crop to soils and crops depend on the amount of biomass that cover crop produces. In the U.S. Corn Belt, cover crops are typically drill-planted in fall after crop harvest and then terminated in early spring. Broadcast interseeding cover crops into corn or soybean one or two months prior to harvest could increase the duration of optimum growing conditions for cover crops. ARS scientists in Ames, Iowa, and University of Nebraska colleagues in Lincoln, Nebraska, tested how broadcast interseeding a winter rye cover crop affected soils, crops, and farm income compared with drilling cover crops after harvest. The experiment was conducted for six years in an irrigated no-till corn-soybean rotation. Interseeding the cover crop slightly increased cover crop biomass yield compared with drilling the cover crop (0.57 vs 0.37 Mg/ha). Interseeding the cover crop had very limited effects on fresh and total carbon contents, soil structure, nitrate leaching, and crop yields compared with drilling cover crops. As expected, both cover crop planting methods reduced farm income compared with systems that had no cover crop due to costs associated with planting the cover crop. Even though at this site interseeding did not significantly improve soils or crop biomass yields, interseeding could outperform drilling at other sites with different environmental conditions. In addition, more years of cover crops may be needed to detect changes in soil properties in this sandy soil. These findings are important to farmers, scientists, and others who want to understand cover crop as a best management practice with potential to enhance the sustainability and productivity of sandy soils.

4. Improved modelling scheme to estimate vineyard water use. Vineyard producers in California are under pressure to sustainably reduce/manage irrigation requirements for vineyards due to increasing limited water supplies from recurring drought conditions. Evapotranspiration (ET) is water evaporated from soil surfaces (evaporation, E) and plant canopies (transpiration, T). ET must be managed accurately to reduce irrigation events while maintaining sustainable grape yields. In this work, ARS scientists in Ames, Iowa, and Beltsville, Maryland, compared two hydrometeorological models that estimate ET over three California vineyards. Both models that use soil and canopy temperatures compared well with ET measurements. The ability to accurately estimate ET over the growing season is essential to reducing the number of irrigation events, which increases water conservation and improves water use efficiency. Results from this work showed that up to a 20% reduction in irrigation water is achievable without adversely impacting yields. Reducing the number of irrigation events during a growing season conserves water and reduces irrigation costs for U.S. vineyard producers.

Review Publications
Kovar, J.L., Papanicolaou, A.N., Busch, D., Chatterjee, A., Cole, K.J., Dalzell, B.J., Emmett, B.D., Johnson, J.M., Malone, R.W., Morrow, A.J., Nowatzke, L.W., O'Brien, P.L., Prueger, J.H., Rogovska, N.P., Ruis, S.J., Todey, D.P., Wacha, K.M. 2024. The LTAR Croplands Common Experiment at Upper Mississippi River Basin - Ames. Journal of Environmental Quality. 53(6):978-988. https://doi.org/10.1002/jeq2.20646.
Ruis, S.J., Kovar, J.L., Wacha, K.M., Carney, D., O'Brien, P.L., Delate, K., Cambardella, C.A. 2024. Organic cropping systems enhance soil health indicators in a Mollisol of the U.S. Corn Belt. Soil Science Society of America Journal. 89(1). https://doi.org/10.1002/saj2.20795.
Blanco-Canqui, H., Ruis, S.J., Mamo, M., Shapiro, C.A., Proctor, C., Parsons, J., Thompson, L. 2025. Interseeding cover crop into an irrigated sandy loam for 6 years: Soil, crop, and economic response. Agronomy Journal. 117(1). https://doi.org/10.1002/agj2.70013.
Sciarresi, C., Thies, A., Topp, C., Eudy, D., Kovar, J.L., Trifunovic, S., Dixon, P.M., Archontoulis, S.V. 2025. Breeding for high maize yields indirectly boosting root carbon in the US Corn Belt since the 1980s. Field Crops Research. https://doi.org/10.1016/j.fcr.2025.109774.
Crespo, C., Kovar, J.L., Hart, C.E., Roth, R.T., O'Brien, P.L., Ruis, S.J. 2025. Long-term field study on corn response to sulfur fertilization in Iowa, USA. Field Crops Research. https://doi.org/10.1016/j.fcr.2025.109990.
Rogovska, N.P., Kovar, J.L., Malone, R.W., O'Brien, P.L., Emmett, B.D., Ruis, S.J. 2024. Impact of tillage, cover crops, and in situ bioreactors on nutrient loss from an artificially drained Midwestern Mollisol. Journal of Environmental Quality. https://doi.org/10.1002/jeq2.20668.
Crespo, C., O'Brien, P.L., Ruis, S.J., Kovar, J.L., Kaspar, T.C. 2024. Thermal time and precipitation dictate cereal rye shoot biomass production. Field Crops Research. https://doi.org/10.1016/j.fcr.2024.109473.
Chatterjee, A., Thorp, K.R., O'Brien, P.L., Kovar, J.L., Rogovska, N.P., Malone, R.W. 2025. Long-term DSSAT simulation of nitrogen loss to artificial subsurface drainage flow for a corn-soybean rotation with winter rye in Iowa. Agricultural Water Management. https://doi.org/10.1016/j.agwat.2025.109464.
Liebig, M.A., Abendroth, L.J., Robertson, G., Augustine, D.J., Boughton, E.H., Bagley, G.A., Busch, D.L., Clark, P., Coffin, A.W., Dalzell, B.J., Dell, C.J., Fortuna, A., Freidenreich, A.S., Heilman, P., Helseth, C.M., Huggins, D.R., Johnson, J.M., Khorchani, M., King, K.W., Kovar, J.L., Locke, M.A., Mirsky, S.B., Schantz, M.C., Schmer, M.R., Silveira, M.L., Smith, D.R., Soder, K.J., Spiegal, S.A., Stinner, J.H., Toledo, D.N., Williams, M.R., Krecker-Yost, J.L. 2024. The LTAR Common Experiment: Facilitating improved agricultural sustainability through coordinated cross-site research. Journal of Environmental Quality. 53(6):787-801. https://doi.org/10.1002/jeq2.20636.
Paciolla, N., Corbari, C., Kustas, W.P., Nieto, H., Alfieri, J.G., Gao, F.N., Prueger, J.H., Alsina, M., Hipps, L.E., Mckee, L.G., Mcelrone, A.J., Bambach, N. 2024. Two-source energy balance schemes exploiting land surface temperature and soil moisture for continuous vineyard water use estimation. Irrigation Science. 43:731-753. https://doi.org/10.1007/s00271-024-00991-x.