Research Project: Strategies to Support Resilient Agricultural Systems of the Southeastern U.S.

Location: Plant Science Research

2021 Annual Report

Objectives
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.

Approach
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.

Progress Report
ARS scientists at Raleigh, North Carolina, suggests 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. New grant-funded project related to the in-house project is testing the impact of management on soil biological nitrogen availability in cotton production systems throughout the Cotton Belt in collaboration with university partners in other states via coordination through Cotton Incorporated. ARS scientists at Raleigh, North Carolina continue to evaluate responses of soybean and wheat germplasm under elevated ozone and heat, with focus on impacts of nutrient source and sink balances between above-ground organs, roots, and root-associated microbes. For soybean, high-yielding cultivar ‘Jake’ exhibits ozone resilience when exposed to a seasonal average concentration of 66 ppb, but showed a 15% yield loss as a result of decreasing seed size, though not seed number, with a higher seasonal average concentration of 87 ppb that exceeds projected ozone air pollution levels in 2030. ARS scientists demonstrated that ‘Jake’ possesses the characteristic of withholding carbon and nitrogen nutrients in source organs to support local growth demands and of recruiting beneficial soil microbes under elevated ozone. A field trial was conducted by ARS scientists at Raleigh, North Carolina with soybean plant introductions previously known to exhibit differential ozone responses to further advance our understanding of the impact of genetic variation on soybean response to ozone pollution. Fiskeby III (ozone tolerant) and Fiskeby-840 (ozone sensitive) soybean genotypes were compared in a comprehensive field investigation. Fiskeby-840 showed significant biomass reduction and a yield loss of 50%, while Fiskeby III only showed 15% yield loss under a seasonal average ozone concentration of 85 ppb. Proteins and metabolites were extracted from different organs of Fiskeby III and Fiskeby-840 during the developmental processes to identify potential ozone tolerance mechanisms. New Temperature Gradient Greenhouse is now fully operational. This system allows for testing the heat stress response of crops to season-long, 24-hour per day, elevated temperature treatments of both +2 and +4°C relative to an ambient air control. A spring study screened wheat cultivars from the Midwest and the Southeast as well as the wheat progenitor ‘Turkey’ for heat tolerance including temperature effects on the microbial communities associated with roots. A summer study is underway to compare the heat stress response of soybean germplasm in a project supported by a grant from the United Soybean Board. Continued progress was made by ARS scientists 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 at ARS Raleigh, North Carolina, breeding lines 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) were screened for ozone tolerance in open-top chambers and for drought tolerance in field plots. Several lines have been tentatively identified as drought tolerant and two of these lines exhibited significant ozone tolerance. These breeding lines represent potential germplasm releases. In related research, these breeding lines are being assessed for a leaf gas exchange trait that limits ozone uptake (ozone exclusion) and increases water use efficiency (retention of soil moisture) while providing the necessary carbon to support plant growth. This project is being supported by a grant from the United Soybean Board.

Accomplishments
1. Soil health conditions characterized under cotton production throughout North Carolina. ARS scientists at Raleigh, North Carolina, believe soils in the southeastern United States have had a long history of cultivation and periods of rampant soil erosion and degradation. However, recent cultivation technologies have focused on conservation management that reduces soil erosion and improves soil functioning. This study aimed to assess the soil health condition for cotton production throughout the state of North Carolina. Using a stratified random sampling for sampling, 120 fields were sampled by ARS scientists at Raleigh, North Carolina, at depths of 0-4-, 4-12-, and 12-24-inch depths. Soil health condition was highly variable depending on inherent soil physical properties and management-dependent soil biological and chemical properties. Soil organic matter and its biologically active components were greater in fields managed with no tillage or strip tillage on a continuous basis compared with conventional disk tillage. Soil pH and soil-test potassium were not affected by tillage system. Cation exchange capacity was greater in fields managed with continuous conservation tillage than rotated with disk tillage for other crops. Soil-test phosphorus was lower with conservation tillage than with disk tillage, but all fields were rated adequate in soil-test phosphorus. Crop rotation sequence with high-disturbance crops like peanut, potato, and tobacco led to reduced soil organic matter. History of cover cropping and animal manure application had some positive effects on soil conditions. Overall, the soil health condition of cotton production in North Carolina is fair but shows great promise for improvement with more continuous use of conservation tillage to build soil-test biological activity from relatively low levels at present.

2. Soil organic carbon sequestration assessed from depth distribution characteristics. ARS scientists at Raleigh, North Carolina, suggest loss of organic matter from soils in the southeastern United States has been extensive due to historical practices of conventional tillage and long fallow periods, resulting in oxidation and erosion. However, conservation agricultural systems (like no tillage, cover cropping, residue management) have been developed and adopted by many farmers in the region and there is likely significant sequestration of soil organic carbon occurring on these farms. Sequestration is the removal of carbon dioxide from the atmosphere and its storage in soil. An ARS scientists at Raleigh, North Carolina, developed a new method of calculating soil organic carbon sequestration that does not require detailed side-by-side comparisons or lengthy investigations over time. This new method requires multiple depth sampling of the soil profile to determine a mathematical distribution of soil organic carbon. Data from several published research projects showed that this method gives comparable estimates as more traditional approaches, but with much less resource expenditure. This approach can be used on private farms to determine the extent of soil organic carbon sequestration. Farmers can potentially benefit from ecosystem markets that make payments based on the amount of carbon stored in soil. This research will help researchers, agronomic advisors, and farmers to better assess agricultural management.

3. Field trials demonstrate that elevated temperature reduces soybean yield and provide guidance to improve crop growth models. ARS scientists at Raleigh, North Carolina, believe rising temperature is one aspect of climate change predicted to reduce crop productivity, however the magnitude of the impact is not known due to lack of exposure systems that provide season-long elevated temperature treatments in the field. ARS scientists and engineers at Raleigh, North Carolina, developed a field exposure system based on technology adapted from air pollution research and used the system to demonstrate a reduction in soybean seed yield of 22% when average daily temperature was increased 3.4 degrees Celsius. A team of crop modelers from Qingdao Agricultural University in China, the Leibniz Centre for Agricultural Landscape in Germany, the University of Florida, and ARS at Ames, Iowa, used the field results to test soybean growth models and found reasonable prediction of seed yield loss, but poor simulation of biomass reduction and crop maturity date. The results demonstrate the need for plant breeding programs to improve the heat stress tolerance of soybean and for identifying areas for improvement in soybean growth models.

4. No evidence for an interaction between elevated temperature and ozone in determining soybean biomass production and seed yield. ARS scientists at Raleigh, North Carolina, suggest climate change involves the interaction of multiple environmental stresses. One limitation in studying these interactions is the lack of exposure systems that provide season-long treatments under field conditions. ARS scientists and engineers at Raleigh, North Carolina, developed a field exposure system based on technology adapted from air pollution research. The system was used to conduct a four-year study to determine the effects of elevated temperature (+3.4 degrees Celsius), elevated ozone (66 parts per billion 12-hour mean), and the combined treatments on soybean biomass production and seed yield. Warming and ozone each had specific effects, but no temperature x ozone interactions were found. The absence of an interaction between ozone and temperature has important implications for modeling plant response to multiple stress factors. The ability to model plant response in complex environments will benefit farmers by identifying management strategies for adapting cropping systems to climate change.

5. Tropospheric ozone rapidly decreases root growth by altering carbon metabolism and detoxification capability in growing soybean roots. ARS scientists at Raleigh, North Carolina, suggest reductions in soybean yields attributed to ozone have been steadily increasing. To confront this environmental challenge and optimize crop yield, scientists have tried to understand how plants respond to elevated ozone. Previously, the studies have generally focused on above-ground tissues rather than the root systems that support plant fitness by absorbing nutrients and interacting with soil microbes to aid crops in their survival against environmental threats and stresses. ARS scientists compared the root structures and protein profiles of ozone-tolerant and ozone-sensitive soybean genotypes grown under elevated ozone conditions. The results produced robust evidence that ozone rapidly decreases root biomass and root diameter by altering key enzymes involved in carbon metabolism and detoxification capability. This finding provides better understanding about how ozone pollution impacts roots and root-associated soil microbes.

6. Impact of elevated ozone on yield and carbon-nitrogen content in soybean cultivar ‘Jake’. ARS scientists at Raleigh, North Carolina, believe ozone pollution is a major environmental threat to the United States economy and its food security. Soybean is one of the major staple crops in the United States, an export valued at $18.7 billion. However, its production has come under ozone threat, with an estimated annual yield reduction of more than 12%. To confront this environmental challenge, optimize crop yields, and thereby maintain food sources for a growing United States and global population, ARS breeders and plant scientists at Raleigh, North Carolina, have been working to develop crops able to withstand environmental stresses. In this study, the high yielding cultivar ‘Jake’ was fumigated in a climate-simulation exposure system under field conditions with elevated ozone pollution comparable to levels estimated to be reached by the middle of the 21st century. Yield loss held at 15% following season-long ozone treatment. The research demonstrated that cultivar ‘Jake’ possesses the developmental strength to retain nitrogen and carbon sources to maintain growth and recruit beneficial soil microbes to support fitness under elevated ozone. This finding provides evidence that cultivar ‘Jake’ will prove suitable as breeding material for a generation of new ozone tolerant lines able to withstand future climate challenges.

7. Soil biological activity and nitrogen mineralization characterized across soil types and management. ARS scientists at Raleigh, North Carolina, suggest the supply of nitrogen to agricultural crops and forages can be partially achieved from mineralization of nitrogen from soil organic matter. A biologically based soil testing tool has been developed for making predictions of soil organic nitrogen mineralization, but needs to be tested under a diversity of climates, land uses, and soil conditions. A scientist from ARS Raleigh, North Carolina, collaborated with a former graduate student at North Carolina State University to evaluate how soil-test biological activity determined from the flush of carbon dioxide following rewetting of dried soil relates to several dozen other soil properties. Soil-test biological activity was most closely related with other soil organic carbon and nitrogen fractions, like cumulative carbon mineralization during 24 days, basal soil respiration, particulate organic carbon, and nitrogen mineralization. Soil-test biological activity and nitrogen mineralization were closely associated across all samples, but diverged somewhat between prairie soils and Blue Ridge, Piedmont, Ridge/Valley, and Coastal Plain soils of the eastern United States. Difference in land use between cropland and pastureland did not alter this association. Soil-test biological activity was verified as a robust indicator of soil organic nitrogen supply, as well as of general soil biological condition to assess soil decomposition potential and potential soil carbon storage.

8. Soil-test biological activity is affected more by long-term than short-term management. ARS scientists at Raleigh, North Carolina, believe living soil breathes! This life can be detected from the carbon dioxide emitted from soil through the actions of soil microorganisms decomposing organic matter. Interest in determining soil biological activity is growing, because of soil health enthusiasm by farmers and various stakeholders devoted to regenerative agriculture. A scientist from ARS Raleigh, North Carolina, collaborated with a visiting scientist from the Federal Technical University of Parana in Brazil to test how much soil-test biological activity changes in response to sampling during a growing crop. Short-term effect of root development in soil was relatively minor (7%) compared with much greater long-term effects from edaphic factors promoted by long-term management (81%). Results indicate that short-term changes in soil-test biological activity are important, but modest compared with variations due to edaphic factors of soil depth and texture. These results will help users of soil-health testing to understand the extent of soil biological changes that can be expected during different sampling periods within the year.

9. Soil water content targeting optimum porosity for microbial activity characterized from water-holding capacity. ARS scientists at Raleigh, North Carolina, believe soil water content for laboratory incubations of soil microbial activity and net nitrogen mineralization has been reported with many different approaches. This study was conducted to see if a simple, standardized approach could be developed. An ARS scientist determined soil water content at saturation, at water holding capacity, and at 50% water filled pore space, the latter of which should be most ideal for soil incubations. Clay and soil organic carbon concentrations greatly influenced water content at these three targeted levels of water retention. A fraction of soil water content at saturation provided the most stable estimate of achieving desired water content of 50% water filled pore space. Gravimetric water content at near-saturation times 0.59 is recommended for further studies. It provided a simple and stable estimate of optimum water for microbial activity. This information will be valuable for soil biological scientists to evaluate large numbers of samples for assessment of soil health.

10. Surface residue mass adjusted for soil contamination with knowledge of carbon concentration. ARS scientists at Raleigh, North Carolina, suggest conservation agricultural systems promote surface residue cover of the soil. Estimating the mass of surface residues is complicated by contamination with soil. A scientist from ARS Raleigh, North Carolina developed an estimation procedure based on routine analysis of samples for carbon concentration. The ash fraction of surface residues and pasture forage biomass was highly negatively associated with carbon concentration of samples. Therefore, as carbon concentration declines below a theoretical level of 45%, great likelihood exists that the sample is contaminated with soil. The equation developed had very low deviation, suggesting that carbon concentration alone would be an effective method to replace the additional analysis of ash fraction. These results will be particularly useful for soil and plant scientists studying agricultural systems with conservation management approaches and should lead to better scientific understanding of how management impacts soil and environmental quality.

11. Geospatial soil nutrient variation characterized on livestock farms in North Carolina. ARS scientists at Raleigh, North Carolina, suggest grazed pastures are sometimes considered a source of nutrient enrichment that can lead to contamination of water receiving bodies. However, limited information is available on the geospatial nutrient distribution on farms having grazing cattle. An ARS scientist collaborated with a team of livestock scientists from North Carolina State University to evaluate geospatial distribution of organic and inorganic nutrients in surface soil on six private farms across three physiographic regions of North Carolina, i.e. the Coastal Plain, Piedmont, and Blue Ridge regions. Soil organic carbon and soil-test biological activity levels were generally greater on farms at higher elevation than lower elevation. Within a farm, fields with perennial forages had greater soil organic carbon and soil-test biological activity than fields with annual forages or a history of recent cropping. Evidence was found of enrichment of soil-test phosphorus and potassium in zones near shade, water, and hay-feeding stations. However, the occurrence was on less than half of the fields and the intensity of enrichment was generally lower than in another study where hay-feeding stations were in the same place year after year. Progressive livestock management with moderate stocking rate, rotational stocking, fall stockpiling for winter grazing, and limited hay feeding were identified as possible reasons for minor geospatial concentration of nutrients on these farms.

12. Soil health conditions improved with better pasture management on farms in the southeastern United States. ARS scientists at Raleigh, North Carolina, believe pasture management is an important land use mixed within cropping, forestry, and urban uses throughout the southeastern United States. Limited information is available on how various pasture management approaches might affect soil health and functioning. A scientist from ARS Raleigh, North Carolina collaborated with a ruminant livestock specialist from North Carolina State University to evaluate how management and environmental characteristics affected soil and forage nutritive values on 92 farm fields in North Carolina and surrounding states. Rotational stocking of pastures led to greater surface residue carbon content than continuous stocking of pastures. Managed grazing of pastures led to greater soil organic carbon content and soil microbial activity than hayed fields due to return of feces to the pasture. Older pastures were of equal or greater forage nutritive value than younger pastures, and these older pastures often had greater soil biological activity and nitrogen mineralization potential. Elevation gradient from the Coastal Plain to the Blue Ridge led to greater forage nutritive values and greater soil organic carbon and nitrogen contents. Fall-stockpiled tall fescue forage responded to nitrogen fertilization more in soils with lower soil-test biological activity, but many pastures had sufficient nitrogen in soil due to cycling through organic matter. These results will be useful to farmers, farm advisors, and nutrient management specialists to make more effective soil management decisions on pastureland in the southeastern US.

13. Fall stockpiled tall fescue retains good nutritive value and supports resilient agriculture. ARS scientists at Raleigh, North Carolina, suggest fall stockpiling of tall fescue pastures is a viable strategy to stretch the grazing season towards more year-round grazing to lower the cost of cow-calf production. How forage nutritive value is affected by nitrogen and phosphorus fertilization in mature pastures has not been a major focus of research, and yet many pastures in North Carolina and surrounding states are well matured. A scientist from ARS Raleigh, North Carolina collaborated with a ruminant livestock specialist from North Carolina State University to evaluate forage nutritive value responses to fertilization on 92 fields in the region. Only small increases in forage nutritive value were observed in response to nitrogen fertilization and essentially no response occurred to phosphorus fertilization. Forage nutritive value was not affected whether tall fescue had novel or wild endophyte association, but was typically greater when pastures were historically grazed than when cut for hay. Older stands of tall fescue pastures were similar or greater in nutritive value as young pastures. Soil texture did not affect forage nutritive value. A gradient of greater forage yield and lower forage nutritive value occurred from the highland Blue Ridge region to the lowland Coastal Plain region. This study demonstrated that fall-stockpiling of tall fescue can be considered an efficient nutrient cycling strategy on many well-established pastures in the eastern United States and many mature pastures may have sufficient nitrogen cycling through mineralization of organic matter that exogenous nitrogen and phosphorus fertilization may not always be profitable.

14. Multi-species cover cropping improves soil biological conditions soon after adoption. ARS scientists at Raleigh, North Carolina, suggest multi-species cover cropping (i.e. growing several different species of cover crops in the same field at the same time) has been promoted as a top-tier conservation approach for growers that want to improve soil health. However, limited data are available in North Carolina to show how effective the practice might be in establishment, biomass accumulation, and its effects on soil properties. A scientist with ARS at Raleigh, North Carolina collaborated with investigators from North Carolina State University, USDA-Natural Resources Conservation Service, and North Carolina Foundation for Soil and Water Conservation to assess changes in soil properties from a series of 31 trials conducted on farmer’s fields throughout North Carolina. Biomass production was good to excellent in about two-thirds of the trials. Greater nitrogen accumulation in cover crop biomass was possible with multi-species cover crops than typical cereal grains due to significant legume proportion of the mix. Soil biological properties were improved in side-by-side strips of multi-species cover crops compared with no cover crops or single-species cover crops, implying that subsequent cash crops would have greater fertility conditions through supply of bio-available nitrogen and improvement in soil physical properties. Soil-test phosphorus and potassium, on the other hand, were often reduced under multi-species cover cropping than without cover crops, suggesting that release of these elements from cover crop residues would be needed. This study demonstrated that the majority of growers can successfully grow multi-species cover crops with high biomass production, and that these cover crops can improve soil conditions to create a more resilient agricultural system.

15. Perspectives shared on integrated crop-livestock systems in different parts of North America. ARS scientists at Raleigh, North Carolina, suggest livestock production in the United States and Canada ranges from small operations with a diversity of farm products to mega-farms with multiple houses of confined animals focusing on a single product. Manure is associated with all livestock sectors and requires a plan for effective utilization if the farm is to be truly sustainable. The migration to larger and more concentrated animal feeding operations in poultry, swine, dairy, and beef finishing during the past half century has allowed processors to streamline supplies to meet market demand for abundant, low-cost livestock products, whether that be for packaged meat, dairy products, or eggs. Livestock manure can be a resource if used to recycle nutrients and build soil health, but it can be a waste and liability if accumulated without a plan for balanced utilization and delivery off the farm. Changing manure from a cost into a value is the only way that balanced food production, environmental quality, and soil and human health can be achieved in this new era of concentrated feeding operations. A scientist from ARS Raleigh, North Carolina, collaborated with colleagues from Cornell University and Agriculture Food and Agri-Food Canada to share perspectives on how livestock manures can be integrated with regional land uses to assess and develop effective strategies. Examples of crop-livestock integration described for New York, British Columbia, and the southeastern United States give stakeholders in the livestock sector potential solutions and opportunities for greater environmental sustainability.

16. Improved nitrogen management with integrated crop-livestock systems developed. ARS scientists at Raleigh, North Carolina, believe cropping system diversification is needed to pursue greater productivity, but also to overcome threats to ecological stability. Intercropping of forages with cereal grains has potential to diversify agricultural operations and close nutrient cycling to reduce losses of nutrients to the environment. A scientist with ARS Raleigh, North Carolina, collaborated with a team of investigators from São Paulo State University and São Paulo Agency of Agribusiness Technology in Brazil to determine corn production with intercropping of tropical forage grasses as a source of forage for cattle consumption that would be ready for grazing during the winter dry season after corn grain harvest. Different nitrogen fertilization timings were applied to test if greater nitrogen availability early in the season was needed to overcome the competitive effects of the intercropped forage on corn grain yield, but that might also be needed for optimizing forage production. Early nitrogen fertilizer input was needed to maintain corn grain yield closer to that of monocropped corn. Intercropping systems were effective at increasing productivity and efficiently utilizing applied nitrogen more effectively. This research demonstrated the value of enhancing cropping systems diversity on agricultural productivity and points to potentially greater sustainability, by producing both cereal grain and livestock forage on the same land during the course of the year. This research will help farmers, extension specialists, and scientists to further refine cropping systems for greater sustainability.

17. Silage production optimized in integrated crop-livestock systems. ARS scientists at Raleigh, North Carolina, believe cropping system diversification is needed to pursue greater productivity, but also to overcome threats to ecological stability. Intercropping of forages with cereal and legume grains harvested for silage has potential to diversify agricultural operations and close nutrient cycling to reduce losses of nutrients to the environment. A scientist with ARS Raleigh, North Carolina, collaborated with a team of investigators from São Paulo State University in Brazil to determine silage production with intercropping of tropical forage grasses as a source of forage for cattle consumption that would be ready for grazing during the winter dry season after corn silage harvest. Different sowing combinations of intercropped forages were tested to overcome the competitive effects of the intercropped forage on silage yield and optimizing forage production. Intercropping systems were effective at increasing overall agricultural productivity. This research demonstrated the value of enhancing cropping systems diversity on agricultural productivity and points to potentially greater sustainability, by producing both silage and livestock forage on the same land during the course the year. This research will help farmers, extension specialists, and scientists to further refine cropping systems for greater sustainability.

18. Soil aggregation and organic carbon improved with cover crop management in Brazil. ARS scientists at Raleigh, North Carolina, suggest winter soil management in the tropical regions of Brazil could be improved with better cover crops to promote soil organic matter accumulation. A scientist with ARS Raleigh, North Carolina, collaborated with scientists from São Paulo State University to determine the best combination of fall cropping and early spring cover cropping to promote soil improvement in a long-term soybean cropping system. Soil organic carbon accumulated with fall planting of ruzigrass (Urochloa ruziziensis) following soybean harvest and cover cropping in early spring with sunn hemp (Crotolaria juncea). Both quality and quantity of crop residues were considered important for sequestering soil organic carbon and improving soil health. These results can be used to better understand how soil health can be improved with different cover crops in the United States as well.

19. Regional data summarized to predict corn grain yield from soil and weather variables. ARS scientists at Raleigh, North Carolina, believe predicting how cereal grains are impacted by soil and weather variables would be valuable to better manage nitrogen fertilizer for optimized production. Grain yield without nitrogen fertilizer application accounts for available nitrogen in the soil system, which can be used to reduce the total quantity of nitrogen fertilizer needed to optimize production and prevent loss to the environment. A scientist with ARS Raleigh, North Carolina, collaborated with lead investigators from Kansas State University and other investigators from Corteva Agriscience, Agriculture and Agri-Food Canada, Iowa State University, University of Minnesota, North Dakota State University, University of Illinois, Michigan State University, and Brigham Young University to assess published data from 1104 field studies conducted between 1999 and 2019. Management factors such as previous crop and irrigation in combination with surface-soil organic matter accounted for the largest portion of variation in unfertilized yield level, while weather features helped refine predictions. A simple framework that included early spring weather variables was just as effective as full-season weather information. Refined prediction of yield without nitrogen fertilizer could help provide key insights for better nitrogen management of corn. This information will be valuable to a network of scientists to work collaboratively, as well as to agronomic advisors in making more effective nitrogen fertilizer recommendations for corn.

20. Applied aspects of soil carbon management summarized in textbook. ARS scientists at Raleigh, North Carolina, believe soil and its microbial inhabitants are vital to ecosystem functioning. A scientist from ARS Raleigh, North Carolina, assembled recent scientific information into a revised textbook on soil microbiology. Sections covered in this chapter on applied aspects of soil carbon included (1) the importance of soil carbon management, (2) tillage effects on soil carbon, (3) organic amendments, (4) managing crop residue removal for biofuel production, (5) carbon sequestration, and (6) soil health. This textbook is expected to be used in undergraduate and graduate classes of soil microbiology by a variety of universities throughout the country.

Review Publications
Franzluebbers, A.J., Pershing, M. 2020. Soil-test biological activity with the flush of CO2: VIII. Soil type and management diversity. Soil Science Society of America Journal. 84:1658-1674.
Franzluebbers, A.J., Poore, M.H. 2021. Nutritive value of fall-stockpiled tall fescue in response to N and P fertilization. Crop, Forage & Turfgrass Management. 113:610-622.
Franzluebbers, A.J., Simioni Assmann, T. 2020. Soil-Test biological activity with short- and long-term carbon contributions. Agricultural and Environmental Letters. 5, Article 20035.
Franzluebbers, A.J., Hunt, D., Telford, G., Bittman, S., Ketterings, Q. 2021. Integrated crop-livestock systems: lessons from New York, British Columbia, and the Southeastern United States. Frontiers of Agricultural Science and Engineering. 8:81-96.
Franzluebbers, A.J., Poore, M.H., Freeman, S.R., Rogers, J.R. 2021. Soil nutrient distribution on cattle farms in three physiographic regions of North Carolina. Agronomy Journal. 113:590-609.
Franzluebbers, A.J. 2020. Holding water with capacity to target porosity. Agricultural and Environmental Letters. 5, Article 20029.
Correndo, A.A., Rotundo, J.L., Tremblay, N., Archontoulis, S., Coulter, J.A., Ruiz-Diaz, D., Franzen, D., Franzluebbers, A.J., Nafziger, E., Schwalbert, R., Steinke, K., Williams, J., Messina, C., Ciampitti, I.A. 2020. Assessing the uncertainty of maize yield without nitrogen fertilization. Field Crops Research. 260, Article 107985.
Franzluebbers, A.J. 2021. Soil organic carbon sequestration calculated from depth distribution. Soil Science Society of America Journal. 85:158-171.
Tisdale, R.H., Zobel, R.W., Burkey, K.O. 2020. Tropospheric ozone rapidly decreases root growth by altering carbon metabolism and detoxification capability in growing soybean roots. Science of the Total Environment. https://doi.org/10.1016/j.scitotenv.2020.144292.
Franzluebbers, A.J. 2020. Carbon concentration predicts soil contamination of plant residues. Agricultural and Environmental Letters. 5, Article 20037.
Tisdale, R.H., Zentella Gomez, R., Burkey, K.O. 2021. Impact of elevated ozone on yield and carbon-nitrogen content in soybean cultivar Jake. Plant Science. https://doi.org/10.1016/j.plantsci.2021.110855.
Crusciol, C.A., Mateus, G.P., Momesso, L., Pariz, C.M., Castilhos, A.M., Calonego, J.C., Borghi, E., Costa, C., Franzluebbers, A.J., Cantarella, H. 2020. Nitrogen-fertilized systems of maize intercropped with tropical grasses for enhanced yields and estimated land use and meat production. Frontiers in Sustainable Food Systems. 4, Article 544853.
Pariz, C.M., Costa, N.R., Costa, C., Crusciol, C.A., Castilhos, A.M., Meirelles, P.R., Calonego, J.C., Andreotti, M., Souza, D.M., Cruz, I.V., Longhini, V.Z., Protes, V.M., Sarto, J.R., Piza, M.L., Melo, V.F., Sereia, R.C., Fachiolli, D.F., Almeida, F.A., Souza, L.G., Franzluebbers, A.J. 2020. An innovative corn to silage-grass-legume intercropping system with oversown black oat and soybean to silage in succession for the improvement of nutrient cycling. Frontiers in Sustainable Food Systems. 4, Article 544996.
Ma, L., Fang, Q.X., Sima, M.W., Burkey, K.O., Harmel, R.D. 2021. Simulated climate change effects on soybean production in Southeastern United States with two crop modules in RZWQM2. Agronomy Journal. 113(2):1349-1365. https://doi.org/10.1002/agj2.20548.
Sima, M., Fang, Q., Burkey, K.O., Ray, S.J., Pursley, W.A., Kersebaum, K., Boote, K., Malone, R.W. 2020. Field and model assessments of irrigated soybean responses to increased air temperature. Agronomy Journal. 112:4849-4860. https://doi.org/10.1002/agj2.20394.
Burkey, K.O., Tisdale, R.H., Zobel, R.W., Ray, S.J., Pursley, W.A. 2020. Interactive effects of elevated ozone and temperature on growth and yield of soybean (Glycine max (L.) Merr.) under field conditions. Agronomy. 10:1803. https://doi.org/10.3390/agronomy10111803.
Mashaheet, A., Burkey, K.O., Saitanis, C., Abdelrhim, A., Rafiullah, R., Marshall, D.S. 2020. Differential ozone responses identified among key rust susceptible wheat genotypes. Agronomy. 10:1853. https://doi.org/10.3390/agronomy10121853.
Abdallah, A., Mashaheet, A., Burkey, K.O. 2021. Super absorbent polymers mitigate drought stress in corn (Zea mays L.) grown under rainfed conditions. Agricultural Water Management. 254:106946. https://doi.org/10.1016/j.agwat.2021.106946.
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