Location: Soil, Water & Air Resources Research2018 Annual Report
Objective 1: Evaluate the impact of temperature and soil water stress on germplasm of corn, soybean, and wheat. Objective 2: Quantify the interactions of water and temperature stresses on energy and carbon exchanges in corn and soybean fields under different management systems. Objective 3: Describe the relationships between ground-based and satellite observed water use and net primary productivity across the Upper Midwest and California. Objective 4: Evaluate agroforestry practice effects on local microclimate, and on crop and forage production, carbon sequestration, and greenhouse gas production.
Development of an enhanced understanding of the impact of temperature and moisture stress on corn, soybean, wheat, and forage phenology and productivity to provide information to incorporate into crop simulation models. Detailed analyses of the impact of different management systems (controlled drainage vs uncontrolled drainage, unsheltered vs sheltered crops) on the energy exchanges and crop productivity of cropping and agroforestry systems will be undertaken. Development of water use and net primary and gross primary productivity maps for the upper Midwest to compare to county level yield maps and evaluation of improved water management techniques. Refinement of crop growth simulation models to improve the understanding of the interactions of carbon-temperature-water under variable conditions. Improved understanding of complex interactions of variable environments on maize phenology, phenotypes, and production across North America.
Observations from analysis of yield gaps on wheat and review of the literature prompted a study to evaluate the interactions between temperature and soil water on winter and spring wheat growth. These studies were conducted in rhizotrons in 2017 and 2018, where environmental variables could be controlled throughout the growing season. Temperature conditions were established to use the 1981-2010 normal temperatures for Salina, Kansas and a temperature regime of normal + 3°C with three soil water regimes, field capacity, 1.25 field capacity, and 0.75 field capacity. Winter wheat was grown using fall seeding and subjected to cold temperatures to ensure vernalization. Weekly measurements of phenology and leaf area were conducted from emergence to maturity with grain harvest and biomass measured at maturity. Grain yield, biomass, and tiller numbers were all reduced under the high temperature regime across all soil water regimes. In the normal temperature environment, both excess and soil water deficit conditions reduced grain yield. Based on our observations of the impact of high nighttime temperatures, we modified the experiment for the spring wheat to use the normal temperatures for Salina, Kansas but only increased the minimum temperatures from sunset to sunrise by 3°C and maintained the same soil water regimes. Increased temperatures increased the rate of development but did not affect tiller numbers; however, grain yield was reduced with the temperature increase at night. Evaluation of the changes in canopy temperature and the linkage to the carbon dioxide and water vapor exchanges has revealed the dynamics of high nighttime temperatures on the carbon balance. Temperatures above 20°C during the night were used as a threshold to compute the number of hours the plant was exposed to warm night temperatures and then accumulated from the beginning of the reproductive period until physiological maturity. The greater the exposure of corn or soybean to high nighttime temperatures the more rapid the rate of senescence as determined by the plant senescence reflectance index and the lower the yield in that year. Evident in these data was the observation that carbon dioxide concentrations within the canopy volume increased during nights with high nighttime temperatures due to increased respiration rates and lack of exchange of air between the canopy volume and the atmosphere. These high concentrations of carbon dioxide are recycled the next day in the photosynthetic uptake by the canopies. Surface energy balance sensor installation has been completed at the Mead, Nebraska field windbreak and Fayetteville, Arkansas silvopasture sites. The eddy covariance systems are operational and additional towers arrayed in a transect from the upwind windbreak are collecting canopy microclimate data at Mead. Canopy measurements and biomass samples are collected every 1-2 weeks to determine the impact of shelter on soybean development and yield. The 2017 harvest data indicated significant corn yield loss in several rows immediately adjacent to the windbreaks but the field average yield was ~15% greater than the unsheltered crop. This difference may be due to storm damage in the open field and also a legacy of manure application to the sheltered field. The eddy covariance flux station at the silvopasture site was installed in March beneath the tree canopy to measure evapotranspiration from the forage canopy. A control paddock is being developed adjacent to the silvopasture to enable comparison of forage ET with and without tree shading.
1. Application of crop water stress index to corn and soybean in the Midwest. Corn and soybean production in the Midwest is subjected to water stress at some point during their growth cycle; however, it is unclear as to the magnitude and the impact of this stress. Quantifying the effect of rainfall variation on ecosystem productivity is required to understand how the absence and the oversupply of water induces plant water stress and affects plant growth. ARS researchers at Ames, Iowa, measured canopy temperatures obtained from infrared temperature sensors coupled with eddy flux measurements was used to quantify the crop water stress index (CWSI) to quantify the impact of water stress on corn, soybean, and prairie net ecosystem production (NEP) in central Iowa from June to August, 2006 through 2015. The relationships between CWSI and NEP, evapotranspiration (ET), and volumetric water content (VWC) were analyzed for these three canopies. Average seasonal CWSI values varied substantially among years and sites, indicating no stress and extreme water stress periods. The CWSI significantly increased with decreasing ET and NEP, signaling that water stress adversely affected transpiration and C assimilation. Prairie CWSI was linearly and negatively related to VWC. Corn and soybean CWSI increased with very dry and wet soil moisture regimes, indicating that corn–soybean cropping systems were negatively affected by both the absence and oversupply of water. The CWSI approach quantifies water stress in different agroecosystems to compare the responsiveness of these systems to the dynamics of seasonal rainfall patterns. Being able to quantify the timing and magnitude to water stress on cropping systems in the Midwest will help evaluate the potential effects of enhancing soil water availability to the crop.
2. Geographic distribution of Palmer Amaranth under climate change scenarios. Herbicide-resistant weeds are increasingly becoming a major challenge for agricultural production worldwide. Palmer amaranth [Amaranthus palmeri (S.) Wats.] is an invasive annual forb that has recently emerged as one of the most widespread and severe agronomic weeds in the United States, due in part to its facility for evolving herbicide resistance. It has invaded several parts of the world, including key agricultural production regions in South America. Climate change will likely exacerbate the challenges of managing this species. ARS researchers at Ames, Iowa, developed a process-oriented bioclimatic niche model of Palmer amaranth to examine its potential global distribution under current conditions and future climate scenarios. The model agreed well with all credible current distribution data. Projected future increases in temperatures will expand potential Palmer amaranth range northward into portions of Canada and Europe. Model projections under current and future climates highlight several agricultural production regions of increasing and emerging risk from this weed.
3. Soil carbon sequestration in agroforestry systems. Understanding how soil organic carbon (SOC) changes under agroforestry system will help define the benefits of incorporating tress into landscape management. Tree windbreaks are a common practice in the Great Plains as these porous barriers enhance crop yields through reduced wind speed and evaporation. Many windbreaks are old and in need of renovation. ARS researchers at Ames, Iowa, collected soil profile samples to 1.25 m depth from 8 sites in 4 states to measure soil organic carbon (SOC) stocks and compare these values with adjacent crop fields. The amount of SOC beneath tree windbreaks was significantly greater than the cropped fields at 5 of the 8 sites. Existing trees can be removed and used for bioenergy feedstock and replaced with fast-growing or better adapted species that will likely continue to enhance SOC accumulation in the profile. Additional measures of SOC effects on soil health indicate that the tree windbreaks also enhance overall soil health. The results indicate that there is variation in SOC distribution due to climate, soil, tree species and crop management.
Dold, C., Hatfield, J.L., Prueger, J.H., Sauer, T.J., Büyükcangaz, H., Rondinelli, W. 2017. Long-term application of the Crop Water Stress Index in Midwest agro-ecosystems. Agronomy Journal. 109(5):2172-2181. https://doi.org/10.2134/agronj2016.09.0494.
Hatfield, J.L., Dold, C. 2018. Agroclimatology and wheat production: Coping with climate change. Frontiers in Plant Science. 9:224. https://doi.org/10.3389/fpls.2018.00224.
Ordonez, R.A., Castellano, M.J., Hatfield, J.L., Helmers, M.J., Licht, M.A., Liebman, M., Dietzel, R., Martinez-Feria, R., Iqbal, J., Puntel, L.A., Cordova, S.C., Togliatti, K., Wright, E.E., Archontoulis, S.V. 2018. Maize and soybean root front velocity and maximum depth in the Iowa, USA. Field Crops Research. 215:122-131. http://dx.doi.org/10.1016/j.fcr.2017.09.003.
O'Dell, D., Eash, N.S., Hicks, B.B., Oetting, J.N., Sauer, T.J., Lambert, D.M., Logan, J., Wright, W.C., Zahn, J.A. 2018. Reducing CO2 flux by decreasing tillage in Ohio: Overcoming conjecture with data. Journal of Agricultural Science. 10(3). https://doi.org/10.5539/jas.v10n3p1.
Kistner-Thomas, E.J., Hatfield, J.L. 2018. Potential geographic distribution of Palmer amaranth under current and future climates. Agricultural and Environmental Letters. 3:170044. https://doi.org/10.2134/ael2017.12.0044.