Objective 1: Develop and deliver reduced- or zero-tillage management practices to maintain surface residues and improve water use efficiency that are adapted to specific low-precipitation dryland wheat growing regions and soils. • Subobjective 1A: Determine if differences in surface soil water and organic matter between no-till wheat–fallow and minimum tillage wheat–fallow are likely to produce a long-term advantage for one system over the other. • Subobjective 1B: Test the effect of delayed minimum tillage on seed-zone water in a very dry region in order to recommend an optimum timing. Objective 2: Develop management practices to increase soil organic matter and associated C and nutrients, reduce greenhouse gas emissions, reduce soil acidification, and maximize long-term soil productivity. • Subobjective 2A: Measure soil organic C and soil organic N stock changes, and carbon dioxide, nitrous oxide and methane fluxes to determine the C and N footprint for six dryland cropping systems, and render this information useful to growers, industry representatives, and policy makers. • Subobjective 2B: Project soil organic C stocks in diverse agroecosystems after changes in tillage and cropping system using the process-based C model CQESTR and climate data. Objective 3: Determine water flux through the soil profile and the potential for N loss in current and proposed cropping systems to determine how to improve the efficient use of water and N through the wheat-root zone in specific dryland growing regions. • Subobjective 3A: Compare water storage, water use efficiency, and nitrate leaching between various winter wheat–fallow systems in a low-precipitation zone. • Subobjective 3B: Quantify the relationship between applied N and N uptake, use efficiency, and grain yield in long-term experiments to develop and apply this information in determining optimum fertilization rates for dryland, no-till winter wheat production. Objective 4: Conduct research and develop approaches to increase soil carbon or improve related soil properties (e.g., soil health; functional optimization of the soil microbiome) that are marked by increased dryland production while at the same time, lowering inputs and improving resilience to weather related and climate-driven stressors.
Hypothesis 1A: No-till increases rainfall storage compared to minimum tillage, but neither system has an advantage in preserving soil C. Approach 1A: 1) Make comparisons in plots at Moro, OR (started in 2004), Pendleton, OR (2006), and Ritzville, WA, (2002). 2) Collect data for four years. 3) Measure soil water, organic C, and yield components. If yield components indicate insufficient heads per area, we will increase the planting rate. Approach 1B: Initiate fallow tillage at delayed timings. Measure water at seeding, wheat emergence and yield. Weighing lysimeters will characterize evaporation rates and storage of spring rain in untilled and tilled soil. A rainout shelter for the lysimeters, alterations of tillage timing, and extending tillage plots by a year are contingencies if the weather makes conclusions difficult. Hypothesis 2A: Tillage and crop residue affects soil carbon and greenhouse gases. Approach 2A: Measurements are made in: 1) wheat fallow under reduced tillage, 2) no-till annual winter wheat, 3) no till wheat–wheat–sorghum sudangrass, 4) no-till wheat–fallow (0, 45, 90, 135, 180 kg N/ha N rates), 5) no-till wheat–pea (also five N rates), and 6) wheat–fallow under conventional moldboard plow (zero and 135 kg N/ha). Total soil C, N, and S, extractable P, pH, NO3-N, and NH4-N, grain and biomass will be determined annually. Soil temperature and water will be monitored. CO2, N2O, and CH4 samples will be collected. Because climatic factors could affect gas flux measurements and time required to detect low N2O fluxes from some treatments, a third year might be required. Approach 2B: Projections of soil C changes in agroecosystems after changes in tillage and cropping system will be made using CQESTR. Phase I: Long-term soil organic C data from six selected GRACEnet and REAP project sites will be used to develop SOC databases. Phase II: Create site-specific files. Phase III: Generate long-term predictions for change scenarios. Phase IV: Quantify effects of rotation, tillage, fertilization, and climate change for each site. If predictions do not fit the data sets, sensitive parameters will be identified and optimized, or the model’s limitations will be identified. Hypothesis 3A: No-till has improved soil water storage, water use efficiency, and reduced N migration through the root zone. Approach 3A: Treatments are no till and reduced tillage. KBr will be placed in a furrow at planting. Soil samples will be collected every two months for four years. Hypothesis 3B: Management that reduces N losses will reduce fertilizer required for crop yield. Approach 3B: We will use long-term plots in wheat–fallow and in wheat–pea rotations, with five N treatments (0, 45, 90, 135, 180 kg N/ha). Micro-plots (1 m2) in select plots will receive 15N at the start of the experiment. Metal frames will be used as 45-cm deep physical barriers. Total N, extractable NH4-N, and NO3-N, and 15N will be measured in soil samples. Plant samples will be collected inside and outside of the micro-plots area to detect potential lateral movement of 15N.
This is the final report for expiring project 2074-11120-004-00D, “Maximizing Long-term Soil Productivity and Dryland Cropping Efficiency for Low Precipitation Environments,” which is undergoing National Program 212 Office of Scientific Quality Review. Our objectives were based on the National Program 212 action plan, which directed research toward improving soil organic matter, carbon and plant nutrients, reducing greenhouse gases emissions, and the efficient use of water and nitrogen. Progress in most major goals was realized over the five years of the project. In support of Objective 1, research was successful in collecting monthly surface soil water and organic matter samples comparing no-till wheat-fallow and minimum tillage wheat-fallow over a period of three years at three sites. Sample processing is finished, and data will be combined with yield and crop data. Plots for Sub-objective 1B were created at a low rainfall site for three consecutive years to compare the effect of timing of initial tillage on soil water at seeding time and crop yield. The data show how seed zone soil moisture is affected by tillage timing in most years, but that total soil water storage is little affected. This research progress on Objective 1 produced sufficient data to help guide farmers in deciding the advantages and disadvantages of no-till and understanding the optimum window for initial summer fallow tillage where no-till is not practical. In support of Objective 2, incremental soil samples were successfully collected from the top 40 inches from traditional winter wheat–fallow under conventional moldboard plow and three alternative cropping systems (winter wheat–fallow under sweep tillage, winter wheat–winter wheat under no-tillage, and winter wheat–winter wheat–sorghum/sudangrass under no-tillage). Soil organic carbon stocks and nitrogen were determined. Weekly carbon dioxide, nitrous oxide, and methane fluxes in these cropping systems were measured for three years. Calculation and comparison of greenhouse gas emission from these cropping systems will be completed, and the carbon dioxide and nitrous oxide carbon footprint for these cropping systems will be reported. The data indicated that continuous winter wheat under no-tillage with a three-month fallow period was the best cropping system to increase soil organic carbon stocks and that cropping systems in semiarid dryland regions are net sinks for methane. This research progress was reported to stakeholders. Carbon results were shared in a white paper with local growers and the Oregon Wheat Grower Liaison Committee to help guide wheat producers in deciding if they could participate in the carbon market. Also under Sub-objective 2A, incremental soil samples were successfully collected to 60-inch depth from traditional winter wheat–fallow under conventional moldboard plow, winter wheat–fallow under no-tillage, and winter wheat–pea cover crop under no-tillage and five nitrogen fertilizer application rates. Yield data indicated that winter wheat–pea cover crop under no-tillage had significantly higher yields compared to winter wheat wheat–fallow under three nitrogen rates (0, 40, and 80 pounds/acre). This research progress was reported to stakeholders and results were shared in a white paper to local growers and the Oregon Wheat Grower Liaison Committee to help guide wheat producers in deciding if they could use legume cover crops to obtain nitrogen from nitrogen fixation and reduce synthetic nitrogen fertilizer input, while increasing wheat yields. Under Sub-objective 2B, a soil carbon saturation algorithm was added to the CQESTR process-based soil carbon model. Measured soil organic carbon (SOC) and climate data from diverse agroecosystems at six ARS locations across the United States were used to validate the modified CQESTR. The model accurately predicted that a sandy loam soil at the ARS in South Carolina was approaching carbon saturation. The CQESTR model was used with climate models and Intergovernmental Panel on Climate Change (IPCC) climate change scenarios to predict the best management practices to retain or increase SOC stocks under residue removal management for biofuel or IPCC climate change scenarios. The simulation results were shared with the ARS locations and were published in a special issue of Environment Quality Journal. Sub-objective 3A was discontinued when the land lease was terminated, and the responsible scientist retired. Under Sub-objective 3B, applied nitrogen (N) fertilizer to the soil and N uptake in wheat grains and residues were determined for the initial samples, and the final samples are currently being analyzed in the laboratory to determine nitrogen uptake by wheat grain, and wheat and pea plants. These results will be combined with wheat yields and soil profile data to determine nitrogen uptake by plants and nitrate movement in the soil profiles and leaching out from wheat root zone under five nitrogen application rates to determine optimum nitrogen fertilizer application rates for a no-till winter wheat-fallow rotation and winter wheat-winter pea cover crop rotations under dryland conditions. Nitrogen use efficiency for winter wheat under the two cropping systems will provide the data needed by dryland winter wheat producers to decide on using legume cover crops in their winter wheat production system to reduce N fertilizer use and improve soil health and resiliency of dryland wheat production while reducing greenhouse gases emission and nitrate leaching to groundwater. Progress during this five-year project resulted in substantial advances in the understanding of soil management, tillage effects, cover crops, and cropping intensity effects on crop residue, soil water, and soil organic carbon under dryland crop production systems.
1. Winter pea cover crop increased soil organic carbon and resiliency to climate change. Winter pea cover crop increased soil organic carbon and resiliency to climate change. Researchers do not know if current conservation practices can maintain soil carbon and wheat yields in a changing climate. Therefore, ARS researchers in Pendleton, Oregon, and Fort Collins, Colorado, used measured and predicted crop yields from the DayCent model to predict soil organic carbon (SOC) stocks from the CQESTR carbon model. This experiment identified the best agricultural management practices to sustain SOC under current greenhouse gas (GHG) emissions levels until the year 2100, and whether GHG emissions will decline after the mid-century peak. ARS researchers found that the SOC is predicted to increase by 45 and 71 pounds per acre per year under the conservation tillage wheat—fallow and wheat—pea cover crop, respectively. If greenhouse gas emissions keep increasing at the current rate until 2100, SOC could only be maintained under conservation tillage winter wheat—winter pea cover crop rotations with 30% wheat yield increases. This information will be used by producers who are interested in cover cropping and improving dryland resiliency to drought under climate change. In addition, it contributes to a cover crop guide and decision support tool, which can be used by researchers, climatologists, and modelers who are interested in climate change and resiliency of different farming systems.
2. Mid-infrared spectroscopy can detect management-induced changes in soil organic carbon. A major limitation to building credible soil carbon sequestration programs is the cost of measuring soil carbon change. ARS researchers at Pendleton, Oregon; Beltsville, Maryland; Lincoln, Nebraska; Mandan, North Dakota; Fort Collins, Colorado; along with researchers at the Woodwell Climate Research Center and Rodale Institute; used current archived soil samples from seven long-term research trials in the United States to test whether diffuse reflectance spectroscopy can detect subtle management-induced changes in soil organic carbon (SOC) at a given site. This was analyzed using mid-infrared (MIR) spectroscopy coupled with the USDA Natural Resources Conservation Service Kellogg Soil Survey Laboratory MIR spectral library. Overall, MIR-based estimates of SOC percentage, with samples scanned on a secondary instrument, were excellent except at two sites with complex cropping systems. The results suggest that large existing MIR spectral libraries can be operationalized in other laboratories for successful carbon monitoring, despite some uncertainty. Diffuse reflectance spectroscopy is a viable low-cost alternative to traditional laboratory analysis of SOC.
3. Electrostatic method to remove particulate organic matter from soil samples. Soil organic matter exists in many forms, including partially and un-decomposed plant materials. Different amounts of these particulates are found at different times of the year, and they are relatively short-lived and therefore cause large variations in organic matter measurements. Extremely small particulates are difficult or impossible to remove by hand, but ARS researchers at Pendleton, Oregon, developed a rapid way to remove much of both large and small particulates using an electrostatically charged surface. Some soil is attracted to the surface also, but the method consistently removed concentrated particulates and reduced measurement variability. This method will facilitate more consistent measurements of long-term soil organic matter. This method can be used by researchers and commercial labs needing more consistent protocols for assessing carbon sequestration and carbon losses.
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