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.
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 report documents progress for project 2074-11120-004-00D, which started in October 2016. Progress was made on all objectives. For Objective 1, monthly collection of soil water in minimum and zero tillage systems continues with only a few winter months missing due to excessive snow or frozen soil. Laboratory soil analysis is proceeding as samples arrive from the field. A preliminary assessment of soil temperature data indicates that precision and repeatability of the measurements are adequate for detecting any substantial treatment differences. Tillage timing treatments, soil sampling, planting and harvesting were successful in 2017, the first year of the study. The application of a second-year of tillage timing treatments was mostly complete by spring 2018. In addition, soil samples were taken before fall 2017 planting. Samples are being taken monthly in untilled plots to monitor evaporation throughout the growing season. In Objective 2, second-year gas samples (carbon dioxide, nitrous oxide, ammonia and methane) were collected and analyzed weekly during the growing season (October- July) and monthly from August to the middle of October after crop harvest in July. The first-year’s soil samples are being analyzed. Long-term data from five Greenhouse Gas Reduction through Agricultural Carbon Enhancement network (GRACEnet) sites and one Resilient Economic Agricultural Practices (REAP) site were utilized in validating the soil carbon model CQESTR. For Objective 3, the second-year application of potassium bromide tracer was completely successful as were the subsequent sampling efforts to trace it through the soil profile. There appears to be potassium bromide trapped in dirt clods on the soil surface of the sweep-tillage treatment, which will complicate management recommendations for producers top-dressing nitrogen onto winter wheat to take advantage of spring rains. Soil nitrate and ammonium were analyzed. Soil and plant samples from 15N-labeled-tracer micro-plots are currently being analyzed.
1. Increased cropping intensity under no-tillage increased soil organic carbon. Tillage and use of fallow in the past decades have greatly decreased soil organic carbon (SOC) in the dryland Pacific Northwest wheat production region. ARS researchers in Pendleton, Oregon, measured SOC in the top 40 inches of soil under five cropping systems and compared their values with SOC stocks predicted with the simulation model CQESTR. Continuous wheat, with a short fallow period and no-tillage, was the only cropping system where SOC increased. Modeling with CQESTR showed that only continuous winter wheat under no-tillage with a 30% yield increase is likely to maintain SOC under a warming climate anticipated by the Third Oregon Climate Assessment Report released in 2017. Continuous cropping under no-tillage not only increases SOC and improves soil health and resiliency to the impact of changing climate, but also provides continuous soil cover that protects the soil from wind and water erosion and increases resistance to drought.
2. Farmers are adopting methods that retain maximum surface residue. Dryland farmers in the Pacific Northwest need to know which crop residue and tillage management strategies are most sustainable and profitable over the long term. ARS scientists in Pendleton, Oregon, collected data using weighing devices to measure storage of rainfall in the soil and subsequent evaporation under different crop residue levels and types of tillage. Regardless of tillage, increasing amounts of crop residue on the soil surface consistently improved water storage, meaning that managing large amounts of surface residue instead of removing or burying the residue results in more water for establishment and growth of winter wheat. Knowing this, growers are choosing equipment and developing farming methods that allow them to retain maximum levels of surface residue such that high-residue no-till farming is becoming the predominant practice in some areas. Increased surface residue improves yield in dry years, improves soil quality, and practically eliminates soil erosion.
3. Cropping intensification increases soil organic carbon stocks more than minimum- or no-tillage. The practice of leaving land fallow to conserve soil water is a major limiting factor to increasing soil organic carbon (SOC) stocks in dryland crop production systems. ARS researchers in Pendleton, Oregon, and Mandan, North Dakota, compared SOC measured in the northern Plains with SOC simulated with the CQESTR model. Changing from a spring wheat-fallow rotation under minimum tillage to continuous spring wheat under no-tillage increased annualized biomass additions by 82% and SOC by 197 pounds/acre/year in the top 12 inches of soil. A more intensive crop rotation such as continuous spring wheat was predicted to increase SOC stocks more than minimum tillage or no-tillage. A warming climate was predicted to have a minor influence on SOC compared to intensifying the spring wheat-fallow rotation with the addition of a second spring wheat or rye crop. Growers and their advisors have new information to guide them in developing agricultural practices that reduce the impact of climate change on crop production.
Nash, P.R., Gollany, H.T., Liebig, M.A., Halvorson, J.J., Archer, D.W., Tanaka, D.L. 2018. Simulated soil organic carbon responses to crop rotation, tillage, and climate change in North Dakota. Journal of Environmental Quality. 47:654-662. https://doi.org/10.2134/jeq2017.04.0161.
Gollany, H.T., Polumsky, R.W. 2018. Simulating soil organic carbon responses to cropping intensity, tillage, and climate change in Pacific Northwest dryland. Journal of Environmental Quality. 47:625-634. https://doi.org/10.2134/jeq2017.09.0374.
Wuest, S.B. 2017. Surface effects on water storage under dryland summer fallow, a lysimeter study. Vadose Zone Journal. 17(1). doi:10.2136/vzj2016.09.0078.
Gollany, H.T., Venterea, R.T. 2018. Measurements and models to identify agroecosystem practices that enhance soil organic carbon under changing climate. Journal of Environmental Quality. 47:579-587. https://doi.org/10.2134/jeq2018.05.0213.
Nash, P.R., Gollany, H.T., Sainju, U.M. 2018. CQESTR simulated response of soil organic carbon to management, yield, and climate change in northern Great Plains region. Journal of Environmental Quality. 47:674-683. https://doi.org/10.2134/jeq2017.07.0273.
Nash, P.R., Gollany, H.T., Novak, J.M., Bauer, P.J., Hunt, P.G., Karlen, D.L. 2018. Simulated soil organic carbon response to tillage, yield, and climate change in the southeastern Coastal Plains. Journal of Environmental Quality. 47:663-673. https://doi.org/10.2134/jeq2017.05.0190.