Location: Soil, Water & Air Resources Research2017 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.
Variation in crop productivity and grain yields exhibit a large variation among years. The differences between attainable yield and actual yield of the crop form the basis for yield gaps. These analyses have been conducted for all counties in the eight Midwestern states and for wheat production in Kansas, North Dakota, and Oklahoma. In previous research it was found that July maximum temperatures, August minimum temperatures and July-August precipitation explained the yield gaps across the Midwest. When these results were extended into wheat production, it was found that precipitation during the grain-filling period was the dominant factor affecting the yield gap. The progression of crop development across the Great Plains revealed that April precipitation was the primary factor in Oklahoma wheat yields. May precipitation in Kansas, and July precipitation for North Dakota. The changes in crop productivity is one of the key indicators being used to assess the long-term impacts of climate on agriculture. One of the critical questions involves the dynamics of carbon and water from corn and soybean production systems. Using our long-term data sets collected over corn and soybean we have been able to show that these production systems are carbon negative. When these crops are grown under conventional tillage there is a loss of 1915 kg per hectare per year (1685 pounds per acre per year). This continual loss of carbon from the soil reduces the water holding capacity and nutrient cycling in these soils. This creates a condition in which these production systems are more susceptible to weather variation within and among growing season. To address this question, we have established measurement sites in fields with cover crops and no-till systems to have a direct comparison with conventional tillage systems. These fields were sampled with soil cores at a 50 m grid to a depth of 1.2 m to be able to relate soil carbon measurements with the micrometeorological method over time. The interactions of carbon and water in the soil are affected by the biological activity in the soil. An evaluation of the factors that sustain biological activity are a consistent food source, a moderated soil microclimate, adequate soil water, and minimal disturbance of the soil. The detailed observations we have collected in the field for corn and soybean crops have revealed why the impact of high nighttime temperatures during grain-filling is detrimental to grain yields. Observations of within canopy measurements of carbon dioxide and water vapor have shown that hot nights (greater than 27°C) increases the respiration rate and releases carbon dioxide to the atmosphere so the net carbon flux for these days is nearly zero. This shows that exposure to these conditions doesn’t provide any net accumulation of carbon for grain-filling. Conversely, observations of carbon exchange at night when the temperatures are cool (less than 15°C) show a large positive value of carbon uptake. Data sets have been complied using a constellation of flux towers over corn and soybean crops in central Iowa deployed in 2016 to compare to the observed carbon dioxide concentrations from the Orbital Carbon Observatory (OCO-2) platform. This platform provides a measure of solar-induced florescence (SIF) which provides a measure of crop stress. The preliminary data from 2016 showed the value in the SIF measurements and two field units have been deployed in 2017 to capture continuous measurements of SIF in combination with the micrometeorological and surface temperature data over corn and soybean canopies. These data provide a direct comparison between carbon and water fluxes and crop florescence. A windbreak site has been established near Mead, Nebraska in cooperation with the University of Nebraska to provide a direct comparison of sheltered and unsheltered crops for their carbon and water vapor exchanges and crop stress. Understanding these effects will quantify the value of changing the microclimate on crop response. Agronomic practices were synchronized between the open irrigated and dryland sites and the sheltered fields enabling a direct comparison of microclimate and crop growth. A transect of measurement stations was installed to measure shelter effects on microclimate and crop development with distance from the tree windbreak. Infiltration and penetration resistance were measured within the windbreak and crop field and soil samples taken to determine physical and chemical properties. Soil carbon dioxide flux is being measured in a transect across the windbreak into the field to a distance of 3 times the windbreak height.
1. Soil carbon in Midwest cropping systems reveal continual carbon loss. The changes in soil carbon in different cropping systems is often considered to be slow and only measureable over decades. Using a detailed set of measurements from 2006 through 2015, we evaluated the carbon balance of corn, soybean, and a native prairie site using micrometeorological observations. Using these data, observations of gross primary productivity and net ecosystem productivity can be obtained and these observations are made throughout the year so a complete annual balance can be made. Corn had the highest gross primary and net ecosystem productivity followed by prairie and then soybean. The gross primary and net primary productivity were affected by the differences in precipitation within and among year. The annual carbon balance; however, revealed that all systems lost carbon with the prairie system having only a slight carbon loss. These results demonstrate the complexity of the carbon dynamics over contrasting agricultural systems and the relationship to environmental changes.
2. Crop productivity expected to decline as temperatures warm and precipitation becomes more variable. Projected changes in climate across the Midwest has the potential to impact corn and soybean production; however, there has been little detailed analysis on expected changes at the county or cropping district level. Climate scenarios at the county level were linked with statistical models of yield gaps for corn and soybean to evaluate the changes in yield gaps from 2025 through 2075. Yield gaps increased throughout this period because of the increasing July maximum and August minimum temperatures and increased to 75% in the southern portion of the Corn Belt for corn and 30% for soybean. There was a strong gradient in the magnitude of the yield gaps from north to south for corn and to a smaller degree for soybean. This effect is due to soybean having a higher temperature limit during grain-fill than corn. The adaptation strategies for both corn and soybean production systems in the Midwest reveal that improving soil water availability to reduce crop stress will offset the impact of maximum temperature extremes; however, exposure to higher minimum temperatures is offset by altering the planting date or using a shorter growing season plant to avoid late summer heat stress. Providing an analysis of expected changes in crop production and potential adaptation strategies can help producers begin to consider changes in their production systems to cope with climate change.
3. Tree windbreaks exhibit a large potential to improve soil health. Tree windbreaks have been extensively planted to enhance crop growth in regions of the Great Plains prone to drought. In addition to microclimate enhancement, these plantings also sequester carbon in above- and belowground biomass and the soil. Eight locations in the Great Plains were selected to compare soil properties beneath tree windbreaks with adjacent crop or grasslands (pasture or hay). Soil pits and deep auger samples were taken to enable full soil profile descriptions and data to a depth of 1.2 m. Soils beneath tree windbreaks had on average almost 3 kg m-2 greater soil organic carbon (SOC) stocks than the adjacent agricultural fields. Stable carbon isotope analysis supports the hypothesis that the increased amount of SOC is tree-derived, which likely accumulated due to increased inputs via leaves and roots and lack of soil disturbance. These results indicate that tree windbreaks are likely to enhance overall soil health in addition to their documented microclimate benefits. This information is important for research, extension and forestry staff, and landowners interested in renovating existing windbreaks or planting new windbreaks.
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