Location: Soil, Water & Air Resources Research
2022 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. 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, any change in crop management has potential to 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 each growing season. The first site is under conventional 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. Aspirational management includes 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 has not improved significantly, as evapotranspiration was similar in both cropping systems. Long-term study of the conventional site since 2006 showed that differences in water and light use efficiency among crops vary with weather conditions and season.
Objective 2. Continuous microclimate measurements at the Mead, Nebraska, (tree windbreak) and Fayetteville, Arkansas, (silvopasture) field sites have continued with only minor improvements and modifications. Relatively small differences in air temperature, relative humidity and other microclimate parameters have been observed with distance from the tree windbreak, which are being assessed with regard to crop yield patterns. Microclimate data need to be carefully screened to identify periods of similar wind conditions for assessment of windbreak effects, as wind direction and speed have a large impact on all parameters. Crop yield 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 determine water and light use efficiency for the corn and soybean crops. Light use efficiency for corn ranged from 2.17 to 2.82 grams of grain per mega Joule of intercepted photosynthetically active light with the highest value farthest from the windbreak. For soybean, the range was from 0.53 to 0.88 with the highest value nearer to the windbreak. Additional crop years of measurements and interpretation with various microclimate parameters are ongoing. Light interception measurements were begun at the Fayetteville silvopasture site to enable measurements of light use efficiency of the forage under the trees and at the open control sight. Data from the 2021 growing season indicate that forage canopy development proceeds rapidly early in the spring before haying or grazing. The forage is being grazed in 2022 and the light interception measurements are being repeated.
Accomplishments
1. Heat stress index for grazing animals. Climate change, especially increasing temperatures, have the potential to negatively affect grazing animal performance through reduced forage intake, weight gain, and milk production and also affect reproduction efficiency. One of the potential benefits of silvopasture systems (forages grown beneath widely spaced trees) is improved grazing animal performance due to reduced heat stress. ARS researchers in Ames, Iowa, assessed an animal comfort index for its ability to characterize the microclimate at a silvopasture research site in Fayetteville, Arkansas. Wind speed, air temperature and humidity, and solar radiation were measured beneath the tree canopy and in an adjacent open pasture. The comfort index failed to show less stressful conditions in the shade provided by the silvopasture due to lower wind speeds within the trees. It was concluded that the animal comfort index used, which was developed for livestock feedlots, was not suitable for grazing animals due to differences in surface conditions between feedlots and pastures. Feedlots generally have concrete or bare soil surfaces that store and transfer heat differently than a forage canopy. An entirely new comfort index for grazing animals will need to be developed that couples ongoing microclimate measurements with monitoring of livestock temperature and performance under open pasture and silvopasture conditions.
Review Publications
Amorim, H., Ashworth, A.J., Zinn, Y.L., Sauer, T.J. 2022. Soil organic carbon and nutrients affected by tree species and poultry litter in a 17-year agroforestry site. Agronomy Journal. 12(3). Article 641. https://doi.org/10.3390/agronomy12030641.
Ashworth, A.J., Kharel, T.P., Adams, T.C., Sauer, T.J., Philipp, D., Thomas, A., Owens, P.R. 2022. Spatial monitoring technologies for coupling the soil plant water animal nexus. Scientific Reports. 12. Article 3508. https://doi.org/10.1038/s41598-022-07366-2.
Jiang, Z., Owens, P.R., Ashworth, A.J., Fuentes, B.A., Thomas, A.L., Sauer, T.J., Wang, Q. 2021. Evaluating tree growth factors into species-specific functional soil maps for improved agroforestry system efficiency. Agroforestry Systems. https://doi.org/10.1007/s10457-021-00693-9.
Wang, Z., Thapa, R., Timlin, D.J., Li, S., Sun, W., Beegum, S., Fleisher, D.H., Mirsky, S.B., Cabrera, M., Sauer, T.J., Reddy, V., Horton, R., Tully, K. 2021. Simulations of water and thermal dynamics for soil surface with residue mulch and surface runoff. Water Resources Research. 57. https://doi.org/10.1029/2021WR030431.
