Project : USDA ARS

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Research Project: Linkages Between Crop Production Management and Sustainability in the Central Mississippi River Basin

Location: Cropping Systems and Water Quality Research

2024 Annual Report

Objectives
Objective 1: Determine linkages between plant available water, evapotranspiration, and crop yields. 1a: Determine the relationship between crop yields and available soil water. 1b: Develop spatially explicit field-scale water budgets using remote sensing. 1c: Determine the ability of the APEX model to simulate the spatial variability of crop yields and soil moisture. Objective 2: Characterize and quantify the sub-daily variability in water quality and identify the drivers of that change. 2a: Identify and quantify stream sub-daily water quality variability. 2b: Identify the drivers for phosphorus sub-daily variability. Objective 3: Determine and characterize the effects of management on water use efficiency, nutrient use efficiency, GHG emissions, productivity, and ecology. 3a: Compare WUE and water budget components of different crops and cropping systems. 3b: Integrate corn incremental N use efficiency (NUE) into fertilizer recommendations. 3c: Determine the effects of conservation practices and crop rotations on greenhouse gas and productivity, and the potential trade-offs. 3d: Determine how conservation practices and crop rotations affect above ground biomass and ecology. Objective 4: Evaluate ASP (aspirational) and BAU (business-as-usual) production systems for water quantity, water quality, soil, biological, production and profitability outcomes. 4a: Investigate trade-offs between productivity and environmental metrics for more diverse cropping systems. 4b: Create publicly accessible data holdings for publishing CMRB production and environmental data. 4c: Extrapolate the BAU and ASP water budgets developed at field scale to larger scales.

Approach
The overall purpose of the project is to identify how conservation practices affect outcomes, what cropping systems improve short- and long-term sustainability, and the trade-offs between environmental and production outcomes; and provide that information to producers to help them move toward more sustainable agricultural systems. Objective 1 focuses on the relationship between crop yields, soil moisture content, and evapotranspiration within the context of these soils. Objective 3 compares multiple outcomes of different agricultural systems. The conclusions of these two objectives will help identify important processes that improve agricultural sustainability, provide the information necessary to develop metrics that describe this sustainability, and evaluate trade-offs between environmental and production outcomes of agricultural systems. Objective 4 connects to these two objectives by bringing the information to stakeholders. It will also scale results related to water availability and movement to a larger scale. The research in Objective 2 is needed to incorporate issues of phosphorus transport when scaling phosphorus losses from the edge-of-field to the watershed scale and evaluate environmental impacts. The project will conduct experiments at multiple scales ranging from small plots to watersheds, adding measurements and continuing those already underway. The project builds upon the research infrastructure developed in collaboration with the University of Missouri at our research farm in Centralia and elsewhere, which was enhanced for the Central Mississippi River Basin (CMRB) site of the Long-Term Agroecosystem Research Network (LTAR) starting in 2015. This infrastructure includes small plots, large plots, and fields on which the Common Experiment—a coordinated experiment across LTAR—has been implemented, and the observatory, which provides long-term data of weather and stream flow quantity and quality in multiple nested watersheds. The proposed research focuses on surface and soil water in row crop production systems in the CMRB, with simultaneous consideration of productivity, nitrogen use, greenhouse gas emissions, soil health, and biodiversity. Specifically, research will address the immediate and long-term relationships between row-crop production practices and water budgets, surface water quality, hazardous algae blooms, GHG emissions, ecology, and aboveground and soil biodiversity. The project will result in information that producers and policy makers can use to incite changes in cropping systems.

Progress Report
Progress was made on all four objectives, all of which fall under the four components of National Program 211. In support of Sub-objective 1A we have installed soil moisture sensors in 18 of our 600-foot long experimental plots at the top of the slope and in the middle, where the slope is greatest. They are installed relative to soil layers: one or two above the claypan (the restrictive layer that restricts infiltration), one in the claypan, and one four inches below that. These installations were successful and soil moisture data are coming in through dataloggers and telemetry. With that and the soil moisture sensors installed in the adjacent field last year, we have all the soil moisture monitoring infrastructure and will have all the data we need for this project. In support of Sub-objective 1B, the collaboration with ARS scientists in Beltsville, Maryland, has resulted in remote sensed evapotranspiration ( ET) images validated with water budget numbers at watershed scale. We have started writing the code to analyze remote sensed ET and crop yields. In support of Sub-objective 1C, we have updated the representation of the plots in our computer simulation models with more accurate spatial and temporal information on the crop management. We have developed automated tools that identify inconsistencies and errors in this management and build model input files. These tools also drive an automated calibration process. We are exploring the sensitivity of model parameters to dry and wet weather. In support of Objective 2, we continue to collect high-frequency water quality data at one of our stream gage stations with a phosphorus probe and a water quality probe that measures pH, dissolved oxygen, electrical conductivity, and turbidity. This spring, we had malfunctions of both the phosphorus probe and two of the sensors on the water quality probe. These problems are being resolved. We continue to collect monthly water samples at that location and send them to our Oxford, Mississippi, collaborators for algal content determination and collaboration in a cross-site study. The study investigates the sensitivity and limitation of algae growth to nutrient concentrations. Progress was made in all sub-objectives of Objective 3. In support of Sub-objective 3A, we collaborated on an analysis of water use efficiency (WUE) for different agricultural systems at different locations across the range of precipitation that exists within the Long-Term Agroecosystem Research (LTAR) Network. The analysis has determined the relationships between annual precipitation and above-ground net primary production (ANPP) and showed that the management of croplands provides a buffer to precipitation variability. In support of Sub-objective 3A2, we have continued to collect and process eddy flux data, which are transmitted to the Ameriflux site. We have analyzed the eddy flux and soil moisture data available since 2015 to detect whether the incorporation of hay in the rotation had changed the water balance and the movement of water in the soil profile. However, we have found that the quality of soil moisture data collected at the foot of the eddy flux tower since 2015 is not sufficient. It has become evident that we need to change the installation of the deeper sensors, and replace the sensors installed vertically in PVC tubes with others installed horizontally. Data collection to support Sub-objective 3C continued in fiscal year (FY) 2024. Greenhouse gas emission data and all agronomic data (e.g. aboveground biomass, grain yield, and nutrient concentration) have been processed and are undergoing final quality checks and calculations. Similarly, data collection to support Sub-objective 3D1 was completed for the FY2023 crop in the plots that have prevailing and alternative management practices; it continues with the FY2024 crop. In support of Sub-objective 3D2, we have continued measuring biodiversity in the native prairie and in the cropping systems that use prevailing and alternative practices. Two graduate students collected data and samples every other week for a total of eight sampling dates over the 2023 growing season and they are collecting samples and data monthly in the 2024 growing season. We archived all the samples. The high sampling frequency was implemented to assess the optimal timing and temporal frequency of the measurements for a meaningful comparison of the diverse systems. Objective 4 is directly related to Long-Term Agroecosystem Research (LTAR) Network objectives of evaluating the cropping systems with prevailing and alternative practices for a suite of indicators. Our contribution to the development of the LTAR indicator framework supports Objective 4A1. In collaboration with several LTAR working groups, we have continued to work on the publication of protocols for the measurement, quality assurance, and quality control procedures for the metrics needed to evaluate these agricultural systems. These 40 protocols are currently under review, and available internally to all LTAR scientists and by request to external users; they are being published this summer as a major LTAR output. Water quantity and quality data collection has continued (Sub-objective 4A2), and scientists have certified the 2020 and 2021 data on production, all water quantity variables, and all water quality variables. Certification of FY2022 data is under way. The backlog of water quality samples is now down to six months (from 18 months) thanks to the purchase of new ion chromatography equipment. Total nutrients (nitrogen and phosphorus) from FY2019 and later are now processed. Ameriflux scientists reviewed and audited our data collection and processing processes during a virtual site visit and did not find any issue. Eddy flux data were uploaded to the Ameriflux website up to December 2023. A carbon budget was developed, which uses eddy flux data from the prevailing and alternative practices fields, crop removal based on yields, and soil samples. Initial findings show that alternative practices capture more carbon than practices currently prevailing in the region. Moreover, the carbon capture from the alternative practices was consistent with the goals in the “4 per mil” initiative (Accomplishment #1) initiated during the 21st Conference of the Parties (COP), which aims to increase soil organic carbon by 0.4% per year to compensate greenhouse gases emissions. In support of Sub-objective 4B1 and under the leadership of the Research Data Advisory Team (RDAT) and the Columbia LTAR site, we have secured access and use of the Socrata data management platform. This platform enables the different sites to upload, share and publish data. Our common experiment and long-term observatory data on production, soil, weather, flow, and water quality are ready to be uploaded to this platform. Over the summer, we will continue to work with LTAR to define the templates for the upload and certify the FY2022 data. A manuscript on the selection process and the benefit of this platform is being developed within the RDAT. In support of objective 4B2 and with the help of the Partnerships for Data Innovations, we have developed an app that hydrologic technicians use to record maintenance operations on field monitoring equipment (sensors, dataloggers, flumes, etc.) The timely recording of these operations improves the quality of our data and facilitates the quality control process. We have implemented the quality control procedures defined in FY2023 for water stage and soil moisture values. We also defined and implemented a process to identify and fill in temperature and precipitation gaps using secondary sensors and surrounding precipitation gages. We have developed a gap-filled temperature and precipitation dataset for our site. Finally, we have identified and hired a post-doctoral student to support Objective 4C and work has started.

Accomplishments
1. Conservation practices increase soil carbon by levels consistent with those required to offset carbon emissions. Climate smart agricultural practices have received considerable attention in recent years for their potential ability to remove carbon dioxide from the atmosphere via photosynthesis and store it in the ground via root and residue decomposition. One initiative proposed by the French government and adopted by international organizations, ‘4 per mil’, aims to increase carbon storage in agricultural fields to offset carbon emissions. However, there is limited evidence that climate smart practices achieve this goal. Part of the challenge in evaluating climate smart agricultural practices is that the traditional methods measure carbon in the soil, and do not actually measure if carbon was removed from the atmosphere. ARS researchers at Columbia, Missouri, along with a University of Missouri researcher, used soil samples as well as the state-of-the-art eddy covariance (EC) technique to measure the carbon dioxide removed from the atmosphere in a field with practices that prevail in the region (BAU) and a field with climate-smart conservation practices (ASP). The soil samples and EC techniques showed that the ASP field had more carbon uptake than the BAU field, and that the ASP field had carbon uptake consistent with the amount required to meet goals in the “4 per mil” initiative. Results from this study are useful for stakeholders involved in the measurement, monitoring, reporting, and validation of soil carbon uptake. We illustrate the value of conservation practices in a changing climate as well as the value of eddy covariance measurements for assessing soil carbon.

2. Conversion of croplands to native grasses impacts the water budget by altering evaporation. The Conservation Reserve Program (CRP) promotes planting native, warm-season grasses. In the 12-state U.S. Midwest region, the most recent report suggests there are more than 1.3 million acres planted with native warm-season grasses as part of CRP. However, there is no consensus on the direction of change in evapotranspiration (ET), the amount of water moving from the soil or the plants to the atmosphere or the mechanisms controlling changes resulting from conversion between croplands and prairies, making it difficult for water managers to anticipate impacts of land conversion on water resources. In this study ARS scientists at Columbia, Missouri, and St. Paul, Minnesota, along with university collaborators, used measurements of ET at three locations within the Long-Term Agroecosystem Research Network that have paired cropland and prairie sites. Surprisingly, we found that in the two northern sites, the croplands had higher ET than the prairies, particularly during springtime when the croplands were fallow. The opposite was true at the Missouri site. We used mathematical analysis of the energy budget to show that a parameter called the surface conductance controls the differences in ET between the croplands and prairies. During springtime in the northern prairies, the standing, dormant vegetation blocks transfer of water vapor from the land surface and limits the ET. This work provides a mechanistic explanation for previous contrasting results about whether conversion from cropland to prairie increases or decreases ET and will be useful for water managers in the Mississippi River basin.

3. Topsoil depth controls plant water availability, positively impacting plant water use, biomass, and grain yield. Soil erosion across the U.S. Corn Belt has resulted in cropland with highly variable topsoil depths. Precision agriculture techniques were developed to improve yields and minimize variability in profit in fields with variable soils. In the Central Claypan region of the U.S. Corn Belt, many precision agriculture techniques were based on the assumption that topsoil depth controlled plant available water, and therefore yield. However, this assumption had not been well tested with observational evidence. In this study, ARS scientists at Columbia, Missouri, measured the soil water content, plant water use, and end of season plant biomass and yield for maize plants in three locations with different topsoil depths (shallow, medium, and deep topsoil) within a single field. These measurements showed that deeper topsoil stores more water throughout the growing season. This translates to higher plant water use over the growing season, which results in larger plants and higher grain yield. The understanding that in-field variability in yield is related to plant water use provides evidence to support the development of new precision agriculture techniques. Our findings also suggest that practices that improve soil water holding capacity will likely result in increased crop yields, which is always of interest for producers.

U.S. DEPARTMENT OF AGRICULTURE

Cropping Systems and Water Quality Research: Columbia, MO