Location: Plant Science Research2020 Annual Report
Objective 1. Assess conservation agricultural systems for the capacity to enhance productivity, reduce environmental impacts, build strong rural connections, and be profitable. Objective 2. Develop soil biological testing to improve nitrogen fertilizer recommendations for grain and forage crops. Objective 3. Identify crop stress-tolerance traits, assess germplasm and identify genetic sources of these traits for cultivar improvement. Sub-objective 3A. Identify sources of heat stress tolerance in soybean and wheat. Sub-objective 3B. Identify sources of ozone tolerance in soybean and wheat. Sub-objective 3C. Characterize root architecture under heat or ozone stress. Sub-objective 3D. Characterize the impact of heat, ozone stress, and management on the microbial communities associated with plant roots.
Two long-term field experiments located at the Farming Systems Research Unit at Goldsboro, North Carolina, are the basis for the research on conservation agricultural system evaluation. One experiment compares conventional cropping, organic agriculture, integrated crop-livestock system, plantation forestry, and a naturalized fallow. Soil samples from all treatments will be tested periodically for soil organic carbon and nitrogen fractions, bulk density, water infiltration, and penetration resistance. Crop, animal, and timber production data will be used to assess the trajectory of sustainability from different farming systems. Intact root systems will be characterized for long-term management effects on microbial communities associated with roots using DNA technology (see below). The second long-term field experiment is an agroforestry study with the presence or absence of trees with the alleys planted to native warm-season grasses and tested for effects of harvest management. Forage, animal, and timber production data along with soil resource data will be used to assess the sustainability of the different types of forage utilization and type of shade management for cattle. Soil biological testing to improve nitrogen fertilizer recommendations will be conducted on research stations and on-farm trials. Treatments will be a series of different nitrogen rates to determine yield response of a crop to supplemental nitrogen. Soil biological activity will be determined with the flush of CO2 following rewetting of dried soil method and results used to develop site-specific fertilizer recommendations. Soybean and wheat germplasm selected in consultation with plant breeders will be screened for response to heat stress and elevated ozone. Plant response to heat stress will be assessed based on yield and harvest index using temperature gradient greenhouses and Air Exclusion System (AES) field technology to impose elevated temperature treatments. Plant response to ozone stress will be assessed based on foliar injury and yield using greenhouse chambers and open-top field chambers (OTC) to provide elevated ozone treatments. Genotype differences in biochemical (antioxidant enzymes and metabolites) and physiological (chlorophyll fluorescence, photosynthesis, respiration, and stomatal conductance) processes will be characterized to identify useful traits for phenotyping during development of cultivars with improved stress tolerance. Plants evaluated for heat stress and ozone tolerance will also be assessed for differences in root morphology and root-associated microbes. Root systems will be divided into root classes and assessed for genotype and treatment effects on biomass, diameter and length using high resolution scanners and WinRhizo software. Root associated microbes will be separated from roots and the rhizosphere DNA isolated. Bacterial/archaeal and fungal primer pairs will be used to amplify rhizosphere bacterial 16S rRNA genes and fungal Internal Transcribed Spacer regions (ITS1, ITS2). After sequencing, 16S rRNA sequences and ITSs will be analyzed to characterize genotype and stress effects on root associated microbial communities.
Soil and plant analyses continue to be determined from long-term projects, including an agroforestry project under silvopasture management and a farming systems experiment in Goldsboro, North Carolina. Expired grant-funded projects related to the in-house project explored the impact of management on soil biological nitrogen availability, development of a suitable soil test for organic nitrogen availability to various crops, including corn, wheat, and tall fescue pasture, and assessment of changes in soil health with adoption of multi-species cover crops on farms in North Carolina. ARS researchers at Raleigh, North Carolina, continue to investigate the impact of abiotic stresses on root architectures and root-associated microbial communities. By comparing root morphological and proteomic changes between contrasting genotypes— Mandarin (Ottawa) (ozone sensitive) and Fiskeby III (ozone tolerant)— ARS researchers at Raleigh, North Carolina, found ozone rapidly reduces root biomass and fine root diameter. These changes were associated with decreased expression of enzymes involved in carbon metabolism and the tricarboxylic acid cycle in Mandarin (Ottawa). Ozone tolerance in Fiskeby III roots is associated with ozone-dependent induction of enzymes involved in glycolysis and ozone independent expression of enzymes involved in the ascorbate-glutathione redox cycle. ARS researchers at Raleigh, North Carolina, are currently testing the hypothesis that ozone indirectly alters the root-associated microbial community and function by altering carbon and nitrogen balance between source and sink tissues in a commercial soybean cultivar in the field using our Air Exclusion System. Ozone significantly impaired photosynthesis and decreased leaf area, root biomass, root nodule size and quantity, seed size, and ratio of nitrogen between leaves and roots. Ozone effects on the root-associated microbial community are being studied using DNA approaches with DNA library construction and sequencing planned during the summer of 2020. Significant progress was made by ARS researchers at Raleigh, North Carolina, toward the objective of transferring abiotic stress tolerance genes from plant introductions into germplasm useful for developing new cultivars. In an ongoing collaborative project with plant breeders in the Soybean and Nitrogen Fixation Unit at Raleigh, North Carolina, breeding lines have been developed from hybridization of Fiskeby III or Fiskeby V (both ozone and drought tolerant with low yield potential) with the elite southern cultivar Holladay (stress sensitive with high yield potential). Selected lines were screened in 2019 for ozone tolerance in open-top chambers and drought tolerance in field plots (hopefully to be repeated in 2020). Several lines were tentatively identified as drought tolerant and two of these lines exhibited significant ozone tolerance. If confirmed, these breeding lines present potential germplasm releases. Further analysis of leaf gas exchange was conducted by ARS researchers at Raleigh, North Carolina, with Fiskeby III and Fiskeby V and the advanced soybean breeding lines from the Fiskeby x Holladay crosses. The results supported the concept that a common mechanism contributes to both ozone and drought tolerances. The leaf trait is expressed as a reduction in stomatal conductance while maintaining high rates of photosynthesis. This combination limits ozone uptake (ozone exclusion) and increases water use efficiency (retention of soil moisture) while providing the necessary carbon to support plant growth. The results suggest that a single trait may contribute to multiple stress tolerances.
1. Soil-test biological activity can predict nitrogen fertilizer adjustments for corn. Soil testing for nitrogen availability is now possible with a rapid and reliable indicator that assesses soil biological activity. An ARS scientist at Raleigh, North Carolina, evaluated corn grain yield response to sidedress nitrogen application in a series of 111 field trials throughout North Carolina, South Carolina, and Virginia. Yield response to sidedress nitrogen application validated an earlier finding that supports use of soil-test biological activity as an indicator to modify nitrogen fertilizer requirements on a site-specific basis. Strong association occurred between soil-test biological activity and net nitrogen mineralization. Management systems that promote soil health with greater soil-test biological activity are able to provide a greater supply of nitrogen that can be used to lower nitrogen fertilizer costs and overcome potential nitrogen deficits during adverse weather conditions. Adjustment of nitrogen fertilizer rates based on cost-to-value threshold (i.e. fertilizer cost to grain value) should be an important component of any fertilizer recommendation system. This study validated the concept of nitrogen fertilizer adjustment on a site-specific basis with knowledge of soil-test biological activity. These results will be valuable for farmers wanting to make efficient applications of nitrogen to enhance profit and steward natural resources.
2. Soil-test biological activity can predict nitrogen fertilizer adjustments for stockpiled tall fescue. Soil testing for nitrogen availability is now possible with a rapid and reliable indicator that assesses soil biological activity. An ARS scientist at Raleigh, North Carolina, collaborated with a ruminant livestock specialist from North Carolina State University to evaluate fall-stockpiled tall fescue productivity responses to nitrogen fertilizer inputs at 37 field sites in Georgia, South Carolina, North Carolina, and Virginia. More than 60% of field sites had no economic gain from nitrogen fertilization. None of the sites responded significantly to phosphorus fertilizer inputs. Soil organic carbon and nitrogen fractions were predictive of the extent of yield response to nitrogen fertilizer. Soil nitrogen mineralization varied widely among sites and was predictive of the need for nitrogen fertilizer if in short supply. As a quick and reliable alternative, soil-test biological activity was also predictive of the need for nitrogen fertilizer. This study demonstrated that cattle farmers can increase profit by adopting good grazing management principles and adjusting nitrogen fertilizer inputs in response to conserved nutrient cycling in the biologically active organic fraction.
3. Manipulating nitrous oxide emissions under elevated carbon dioxide. Nitrous oxide is a potent greenhouse gas with a global warming potential 300 times greater than that of carbon dioxide. Globally, agricultural soils are a major source of nitrous oxide from microbial processes associated with the use of chemical fertilizers. A team of scientists from Nanjing Agricultural University and Hainan University in China, North Carolina State University, and ARS at Raleigh, North Carolina, showed that elevated carbon dioxide interacts with oxidized nitrogen fertilizer (nitrate) to produce nitrous oxide. In a greenhouse study with wheat, the combination of elevated carbon dioxide and nitrate fertilizer stimulated nitrous oxide emission and the soil microbes associated with nitrous oxide production. In contrast, very little nitrous oxide was produced when plants were supplied with reduced nitrogen in the form of ammonium. Together, these findings suggest that effective management of nitrogen resources may help harness the positive effects of elevated carbon dioxide on crop production, while reducing nitrous oxide emissions from agricultural fields.
4. Leaf trait associated with ozone tolerance in soybean. Ground level ozone is formed by the action of sunlight on volatile hydrocarbons and nitrogen oxides produced during combustion of carbon fuels. Although frequently considered an urban problem, ozone pollution is also a rural problem because weather systems transport the pollutants into agricultural areas. Ozone is toxic to plants, causing visible injury to foliage and a reduction in the growth and yield of sensitive crops such as soybean. Estimates suggest that current ambient ozone levels are sufficient to reduce soybean yield by 10% or more with greater yield losses anticipated if tropospheric ozone concentrations continue to rise. In the absence of international efforts to control air pollution, future soybean productivity may depend on the development of ozone-tolerant varieties. A first step in developing improved cultivars is identification of traits that can be used as selection criteria in plant breeding programs. In this study, a team of researchers from ARS at Raleigh, North Carolina, and North Carolina State University at Raleigh, North Carolina, identified ozone exclusion as a trait in ozone-tolerant Fiskeby III soybeans that reduces ozone damage by limiting ozone uptake into leaves while maintaining high rates of photosynthesis. This finding is being used by ARS plant breeders at Raleigh, North Carolina, to develop soybeans with greater tolerances to both ozone and drought stress.
5. Wheat chromosome associated with ozone tolerance. Ground level ozone is formed by the action of sunlight on volatile hydrocarbons and nitrogen oxides produced during combustion of carbon fuels. Although frequently considered an urban problem, ozone pollution is also a rural problem because weather systems transport the pollutants into agricultural areas. Ozone is toxic to plants, causing visible injury to foliage and a reduction in the growth and yield of sensitive crops such as wheat. Estimates suggest that current ambient ozone levels are sufficient to reduce wheat yields by 7-12% with greater yield losses anticipated if tropospheric ozone concentrations continue to rise. In the absence of international efforts to control air pollution, future wheat productivity may depend on the development of ozone-tolerant varieties. A first step in cultivar improvement is identification of genes that can be utilized in plant breeding programs to develop ozone-tolerant varieties. In this study, an international team of researchers from Egypt and ARS at Raleigh, North Carolina, tested the ozone sensitivity of a set of wheat genotypes with a single missing chromosome in a common genetic background. The researchers identified chromosome 7A to be a major contributor to ozone tolerance in wheat. The results suggest that major ozone tolerance genes in wheat are located on this chromosome.
6. Diversified cropping systems contribute to soil carbon and nitrogen sequestration. Long-term agricultural experiments are an invaluable resource for understanding how management affects soil conditions, as well as how persistent soil, weather, and management conditions affect productivity, profitability, and environmental quality. An ARS scientist from at Raleigh, North Carolina, collaborated with investigators at North Carolina State University to investigate the influence of 19 years of management on soil organic matter and soil biological activity. Conservation agriculture approaches using no tillage, grass-crop rotation, cover cropping, and organic amendments resulted in superior soil attributes for enhancing soil health conditions on a large field-scale experiment in Goldsboro, North Carolina. Managed timber and agricultural abandonment improved soil organic carbon near the soil surface, which allowed significant protection of the soil from erosion and offered opportunities for nutrient retention. However, innovative cropping systems that used rotation of pastures and crops over time and organically managed cropping systems stored more organic matter and allowed greater nutrient availability than other more conventional systems. This information will be valuable for farmers and extension agents to design robust and resilient agricultural management systems in the face of growing threats from climate change.
7. Spatial variation of nutrients affected by winter pasture feed management uncovered. Efficiency of nutrient utilization on farms is increasingly of concern to farmers due to high cost of inputs and to stakeholders in the region due to potential negative environmental effects on water, air, and soil resources. An ARS scientist from Raleigh, North Carolina, collaborated with the Amazing Grazing program at North Carolina State University to determine nutrient distribution on three North Carolina Department of Agriculture research-station farms associated with beef cattle grazing. On two of the three farms (10 to 65 acres each), large spatial variations in nutrients were detected among different zones of the farm. Zones of enrichment were often associated with repeated winter hay feeding in a particular location. Farmers may choose a designated feeding location due to convenience to access road and/or position on top of hills to avoid saturated conditions. Our results indicate that adoption of improved management approaches for grazing management could help reduce large variations in nutrient distribution and subsequent inefficient nutrient use on the farm. These results will help farmers to adopt better management approaches and help society to appreciate the challenges of sustainable livestock production to attain clean water.
8. Longer-term soil nitrogen mineralization predicted from short-term carbon flush. Management to achieve healthy, functioning soil is needed to meet production and environmental goals of sustainable agricultural systems. Soil biological activity and its role in nitrogen mineralization are key components of soil health evaluation. An ARS scientist from Raleigh, North Carolina, conducted an in-depth study to evaluate how short- and longer-term carbon and nitrogen mineralization were associated in five soils from Georgia and North Carolina. Mathematical descriptions of carbon mineralization were consistent and logical, but similar descriptions for nitrogen mineralization were more complicated. However, associations between soil-test biological activity and long-term nitrogen mineralization were logical and consistent. In conclusion, soil-test biological activity offers a simple, rapid, and robust indication of soil nitrogen mineralization. Greater utilization of the tool will inform land managers of the important role that biologically active organic matter plays in nutrient cycling. This understanding is greatly needed so that (a) agricultural systems can become more efficient in nitrogen utilization and (b) agricultural advisers can help growers remain profitable and avoid unnecessary losses of nitrogen to the environment.
9. Measuring soil biological activity requires standardization. Soil health is an important concept that has gained strong traction within the farming community. Biological indicators of soil health are the most controversial due to a variety of approaches being used without sufficient calibration. Scientists from ARS Raleigh, North Carolina, and Columbia, Missouri, collaborated on a project to evaluate two different soil biological activity protocols. Soils from two long-term field experiments comparing a wide range of management conditions in Missouri and North Carolina were tested. Both biological activity protocols gave results that were highly related across a large gradient, but results differed in obvious ways based on differences in specific steps. Although quick soil-test methods are desirable, they still need to adhere to basic principles of analysis. ARS researchers at Raleigh, North Carolina, showed that alternative methods to estimate soil biological activity need to give due attention to temperature and water conditions during incubation. Unnecessary variations or spurious results could otherwise be produced, which are problematic in making interpretations for farmers. Soil-test biological activity is an important attribute of soil health, and although a variety of methods could be possible, some standardization is needed for sound evaluations.
10. Soil-test biological activity protocol defined by soil mass guideline. Soil testing for potential biological activity has become a valuable tool to assess soil health under a diversity of soil types and management conditions. Variations still exist in how this test is performed, and therefore, further methodological assessments are needed. An ARS scientist from Raleigh, North Carolina, evaluated the effect of a wide range of soil weights and size of containers on the accuracy and precision of soil-test biological activity estimates. Five soils were selected from Georgia and North Carolina to obtain a gradient in soil texture and organic matter content. Both accuracy and precision of soil-test biological activity were optimized with a moderate weight of soil from about 50 to 100 g. Random variations were greater at soil weights much less than this target range. Soil testing labs are encouraged to standardize protocols for soil biological activity measurements, and this study showed that a minimum of 50 g of soil should be considered for most consistent and reliable results. These results will benefit commercial and research soil-testing laboratories and the clientele they serve.
11. Agricultural complexity improves soil chemical properties. Changes in soil fertility with the introduction of livestock grazing of cover crops remains an important area of emerging research. An ARS scientist at Raleigh, North Carolina, collaborated with investigators from the Federal University of Parana and Federal University of Rio Grande do Sul in Brazil to determine changes in soil chemical properties from three long-term experiments in southern Brazil as affected by grazing of cover crops. Greater agricultural complexity with grazing of cover crops led to greater soil pH and base saturation and reduced aluminum concentration, at the expense of reduced potassium concentration and copper availability. The integrated crop-livestock system was considered more sustainable because of stabilized crop yields, additional animal weight gain from grazing of cover crops, and greater productivity returns per land area and per nutrient input. This information will be valuable for scientists and farmers interested in designing more productive and sustainable agricultural systems.
12. Greenhouse gas emissions from grazing lands in eastern United States reviewed. Pastureland in the southeastern United States supports a large segment of cow-calf operations. Knowing the greenhouse gas emissions and carbon footprint of these operations is needed to make informed decisions as to how to improve efficiency. An ARS scientist at Raleigh, North Carolina, reviewed literature on greenhouse gas emissions associated with beef production. Although few studies were conducted specifically in the southeastern United States, studies from other regions of the country and around the world served to guide understanding in the region. Enteric methane emissions from ruminant livestock and soil nitrous oxide emissions from fertilized pastures and crops are the two largest sources of greenhouse gas emissions in agriculture. Enhancing nutritive value of feedstuffs and wisely utilizing on-farm sources of nitrogen are two important strategies to reduce greenhouse gas emissions and sequester more carbon in soil as organic matter. This information will be useful to farmers, agricultural advisors, and scientists in the region to design more efficient pasture-based production systems.
13. Combined liming and gypsum reduced soil acidity and improved crop productivity. Humid environments like the southeastern United States and much of tropical Brazil have soil limitations from acidity that limits grain and forage production. Overcoming acidity may not be as simple as applying limestone alone. An ARS scientist at Raleigh, North Carolina, collaborated with scientists at Sao Paulo State University in Brazil to study the impacts of lime and gypsum application to both simple and diverse cropping systems to understand how acidity interacts with soil organic matter. Long-term evaluation over several years showed that liming was efficient at reducing acidity and exchangeable aluminum throughout the soil profile. Application of both limestone and gypsum was the most effective in raising productivity of an integrated crop and livestock system. These results will be useful to scientists, agricultural extension agents, and farmers to better manage soils in humid environments.
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Burkey, K.O., Agathokleous, E., Saitanis, C. J., Mashaheet, A.M., Koike, T. and Hung, Y.T. (2020). Chapter 10. Ozone Effects on Vegetation: A Walk from Cells to Ecosystems. In: Hung, Y.T., Wang, L.K., and N. Shammas eds. Handbook of Environment and Waste Management, Volume 3: Acid Rain and Greenhouse Gas Pollution Control, pp. 357-396 (ISBN-10: 9811207127). World Scientific Publishing Co. Inc, Singapore, 14 August 2020. https://doi.org/10.1142/9789811207136_0010.
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