Location: Soil, Water & Air Resources Research
2021 Annual Report
Objectives
Objective 1: Quantify the water and light use efficiency of corn-soybean and other cropping systems using a range of management practices (cover crops, tillage, N fertilizer, shelter) relative to carbon and water dynamics throughout the year.
Objective 2: Evaluate the effectiveness of microclimates modified by agroforestry practices on production efficiency of row crop and silvopasture systems.
Approach
To fulfill the objectives of this project there are four major research projects: 1) comparison of energy and C exchanges between cover crop and reduced tillage corn-soybean systems compared to conventional systems, 2) comparison of the effect of increased air temperature and soil water availability on wheat growth and productivity, 3) evaluation of the effect of tree windbreaks on crop performance and energy exchanges compared to rainfed and irrigated cropping systems, and 4) comparison of the water and light use efficiency in pasture systems grown under silvopasture and conventional pasture. The research approach utilizes surface energy balance methods to quantify differences among management practices or microclimate modifications. These data are then used to estimate the water use and gross and net ecosystem productivity using daily values across the growing season with a direct contrast of cumulative water and carbon fluxes over a year and over portions of the year to represent different aspects of management systems. Studies on spring wheat will be conducted in the NLAE rhizotron to quantify the effect of increasing minimum air temperatures on phenological development, biomass, and grain yield components under a range of soil water conditions. The windbreak experiment involves a direct comparison of energy balance, biophysical properties, and productivity of rainfed and irrigated crops with rainfed crops protected by a windbreak at the Eastern Nebraska Research and Extension Center. A silvopasture research site in Fayetteville, Arkansas consists of rows of five tree species with orchardgrass in the alleys that is used for grazing and hay. Eddy covariance fluxes will be compared with Bowen ratio and surface renewal estimates in both agroforestry studies. Forage height, biomass, and leaf area index will be measured before each grazing event. Biomass produced and cumulative crop water use from the onset of growth or since the last grazing event will be used to calculate water use efficiency. These objectives focus on components of agricultural systems, provide a suite of observations on a common set of measurements to quantify carbon and energy exchanges, and lead to the direct comparison of water use efficiency and radiation use efficiency of these different systems. One critical aspect in this integration is the collaboration with crop modeling programs to evaluate how crop simulation models can be improved for these management alternatives.
Progress Report
Objective 1 Hypothesis 1.1. Conventional management of corn and soybean production in the Midwest typically includes tillage prior to planting, fertilizer and pesticide application(s), and additional tillage after corn harvest to incorporate the substantial amounts of crop residues into the soil to promote decomposition.
Due to the large amount of corn and soybean acreage in the Midwest, changes in crop management may substantially influence water and light use efficiency of agricultural land at the regional scale. Water and light use efficiency are defined as the amount of water used (i.e. evaporated from plant leaves and soil) and sunlight absorbed per unit of plant biomass or crop yield produced.
Studies were conducted in central Iowa on two sites, each with two adjacent farmer-managed fields, one cropped to corn and the other to soybean. The first site is under typical crop and soil management, while the second site is part of the Upper Mississippi River Basin Long-Term Agroecosystem Research Network (LTAR) of USDA-ARS, where “aspirational” crop management strategies are investigated at the field scale. The aspirational management is one of reduced tillage with a cover crop following the main crop harvest. All four fields were equipped with instruments (eddy covariance stations) to continuously measure energy, water, and carbon flow between the atmosphere and the crop canopy. Water use efficiency in the aspirational crop management system was not improved, as evapotranspiration was similar in both cropping systems. Long-term study of the conventional site from 2006-2015 showed that differences in water- and light use efficiency among crops depend on weather conditions and season.
Data collected with the eddy covariance stations of conventional and aspirational managed fields will be incorporated into the biogeochemical model, DayCent, to improve the mechanistic capabilities to simulate production and water and nutrient fluxes in response to different cropping systems and climatic scenarios.
Objective 1 Hypothesis 1b. Climate trends indicate that increasing average temperatures are driven by rising daily low temperatures rather than rising daily high temperatures. Precipitation trends suggest that rainfall events will be less consistent but greater in intensity.
Controlled environment chambers (rhizotrons) were used to compare the phenological development, soil respiration, and soil water interactions of maize under two temperature regimes. The two regimes were 30-year average Iowa temperatures for each 24-hour cycle and 30-year average Iowa temperatures during daytime with nighttime temperatures increased 3 degrees C. Soil monoliths were maintained at a low or high moisture content to exert water stress on the maize plants. Maize development was monitored weekly until harvest, while soil respiration, soil water content, and temperature were measured continuously throughout the growing cycle.
A second rhizotron experiment also compared phenological development of maize under imposed water stress conditions as in experiment 1 but with stress conditions applied at an early vegetative stage. Maize development was monitored weekly, while soil water content and temperature were measured continuously throughout the experiment. After imposing water stress at the early vegetative stage, plant samples were collected, and analyzed using RNA-sequencing to explore differences in gene expression. Data collected in these runs can be used to identify water stress-related genes that could be used for selection of water-stress traits. The data from these experiments will be incorporated into the biogeochemical model, DayCent, to improve performance in simulating water stress response on plant production.
Objective 2 Hypothesis 2. Continuous microclimate measurements at both Mead, Nebraska, (tree windbreak) and Fayetteville, Arkansas, (silvopasture) field sites have continued with some modifications to enhance data capture. Preliminary analyses indicate relatively small differences in air temperature, relative humidity and other microclimate parameters with distance from the tree windbreak. Data are being carefully screened to identify periods of similar wind conditions for assessment of the windbreak effect, as wind direction and speed have a large impact on all parameters. Crop yield and spatial variability and water use of the sheltered field is being compared with an open site under identical management operated by University of Nebraska-Lincoln collaborators. Eddy covariance flux data, weather data, and other environmental parameters from the tree windbreak site are being used to assist with the comparison of water use efficiency and light use efficiency. Collaboration with University of Nebraska-Lincoln scientists in charge of the open field site is ongoing to make sure that all data from the two sites are being processed in the same way to allow direct comparison. This collaboration will include development of a standard protocol for data analysis. Collaborators on the Fayetteville project have been instrumental in assisting with site management and sensor maintenance at this location that is over 350 miles from Ames, Iowa. Light interception measurements were begun at the Fayetteville site to enable measurements of light use efficiency of the forage under the trees and at the open control sight. The sensors deployed also allowed calculation of a livestock heat stress index. Data from the 2021 growing season indicate that forage canopy development proceeds rapidly early in the spring before haying or grazing. The heat stress index was found to be more sensitive to wind speed than shade effects, indicating that the benefit of shade is reduced if the tree canopy significantly reduces the wind speed.
Accomplishments
Review Publications
Kuang, X., Xiao, R., Xiao, X., Yuan, Q., Sauer, T.J., Davis, D. 2021. Soil carbon dioxide emissions in a sorghum field: Row position and growth stage effects. Agrosystems, Geosciences & Environment. 4(1). Article e20138. https://doi.org/10.1002/agg2.20138.
Adams, T.C., Ashworth, A.J., Sauer, T.J. 2021. Soil CO2 evolution is driven by forage species, soil moisture, grazing pressure, poultry litter fertilization, and seasonality in silvopastures. Agrosystems, Geosciences & Environment. 4(2). Article e20179. https://doi.org/10.1002/agg2.20179.
Ashworth, A.J., Adams, T., Kharel, T.P., Philipp, D., Owens, P.R., Sauer, T.J. 2021. Root decomposition in silvopastures is influenced by grazing, fertility, and grass species. Agrosystems, Geosciences & Environment. 4(3). Article e20190. https://doi.org/10.1002/agg2.20190.
Dold, C., Wacha, K.M., Sauer, T.J., Hatfield, J.L., Prueger, J.H. 2020. Measured and simulated carbon dynamics in Midwestern U.S. corn-soybean rotations. Global Biogeochemical Cycles. 35(1). Article e2020GB006685. https://doi.org/10.1029/2020GB006685.
