Location: Plant Science Research
2024 Annual Report
Objectives
Objective 1:
Quantify sustainability of southeastern US crop and livestock systems (including agroforestry systems such as silvopasture) with indicators of productivity, environmental performance, and socioeconomic acceptability.
Sub-Objective 1.A:
Assess production and environmental impacts from long-term farming system trials as part of the Center for Environmental Farming Systems (CEFS) in Goldsboro, NC, including the Farming Systems Research Unit trial initiated in 1999 and a silvopasture experiment initiated in 2007.
Sub-Objective 1.B:
Assess forage production, soil organic C and N fractions, and root-zone enrichment calculations in response to grassland restoration with switchgrass seeding following initial termination of previous grass stand with no-till and plow-till techniques. Soil organic C and N stocks are important indicators of soil fertility and health of the land; they are the main constituents in soil organic matter (SOM). Our goal is to assess the impact of soil organic matter redistribution and recovery with restoration of grassland following termination of the original sward.
Sub-Objective 1.C:
Synthesize production, environmental, and socioeconomic information from on-going and previous crop and grazing land studies into a series of technology transfer engagements with the USDA Southeast Region Climate hub, including development of tools, guidance documents, and other resources for enhancing outcomes for producers in the region.
Objective 2:
Characterize root-zone enrichment of soil organic matter and soil ecosystem properties of the region’s predominant agroecological farming systems.
Sub-Objective 2.A:
Determine root-zone enrichment of soil organic C and N fractions under pasture-based livestock production systems in Virginia and surrounding states.
Sub-Objective 2.B:
Determine root-zone enrichment of soil organic C and N fractions under conservation cropping systems in North Carolina and surrounding states.
Sub-Objective 2.C:
Develop improved fertilizer recommendation systems based on the contributions of soil-test biological activity, microbial diversity, and community structure affecting mineralizable soil N supply in cotton and warm-season grasses.
Objective 3:
Investigate molecular and physiological mechanisms associated with heat and ozone stress in soybean and wheat germplasm to understand management implications and usefulness for plant breeding.
Sub-Objective 3.A:
Discover shoot and root traits that contribute to heat stress tolerance in soybean and wheat germplasm.
Sub-Objective 3.B:
Discover shoot and root traits that contribute to ozone tolerance in soybean and wheat germplasm.
Sub-Objective 3.C:
Investigate physiological and molecular responses to separate and combined heat and ozone stress.
Sub-Objective 3.D:
Analyze root-associated soil microbial diversity and community that respond to C and N sink-and-source balance between plant and soil under heat and ozone stress.
Approach
Soil organic C and N, particulate organic C and N, soil-test biological activity, net N mineralization, bulk density, water infiltration, penetration resistance, and routine soil-testing analyses will be evaluated from soil collected from two long-term farming system trials located at the Center for Environmental Farming System in Goldsboro NC. The same soil quality tests will be evaluated from soil collected at different depths from trial plots established at eight research station locations in NC and pasture-based livestock production systems in Virginia. Soil aggregation will be from the ratio of water-stable to dry-stable distribution. Soil texture will be from hydrometer for clay and sieve for sand. The sand fraction will be analyzed for particulate organic C and N. Production and performance data from cattle and forage will be collected annually along with soil resource evaluation data. Soil microbiome will be analyzed based on bacterial and fungal sequences. Soil quality and health as well as crop yield and field management practices will be evaluated to develop recommendations for growers. Data will be developed summary and guidance documents related to conservation agricultural systems, such as no-till cropping, cover cropping, distributed animal manure application, diverse crop rotations, managed grazing systems, and agroforestry systems. Scientific reports as well as environmental and socioeconomic information will be synthesized into a series of technology transfer engagements with the USDA Southeast Region Climate hub, including development of tools, guidance documents, and other resources for enhancing outcomes for producers in the region.
Soybean and wheat genetic varieties selected in consultation with plant breeders will be screened for response to heat stress and elevated ozone air pollution using temperature gradient greenhouses (TGG) and open-top chambers (OTC), respectively. Plant physiological and phenotypical traits, harvest indexes, and yield will be evaluated. Soybean and wheat genetic varieties carrying both heat and ozone stress resilience isolated from heat or ozone stress screenings will be planted in the field-based Air Exclusion System (AES) and treated with separate and combined heat and ozone stresses. Photosynthesis rates, chlorophyll fluorescence, as well as day and night respiration will be measured for the same leaf cohort in the early and late developmental stages using Li-Cor 6400RT devices. Leaves used for gas exchange will be harvested to analyze ascorbic acid content and oxidation state as well as proteome. To analyze C and N source and sink allocation dry plant materials will be milled to a fine powder. The percentage of total C and N will be determined using a macro combustion system. Soil and rhizosphere microbes will be collected in the early and late developmental stages for microbiome analyses. Soil microbial diversity and network changes associated with stress resilience under separate and combined elevated ozone and heat stress will be characterized and coordinated with plant physiological and phenotypical results.
Progress Report
The following activities contributed to Objective 1 to quantify sustainability of southeastern agricultural systems with indicators of productivity, environmental performance, and socioeconomic acceptability.
Typical tall fescue pastures grow with symbiotic fungi that help plants to cope with harsh summer conditions but also produces toxic compounds affecting herbivore performance and production. Renovating tall fescue pastures to allow planting of friendly endophyte-infected tall fescue is promoted. Annual forages can reduce the economic cost of renovation by providing high-quality forage during this transition. How annual forages affect soil health during pasture transition has not been well described. An ARS scientist in Raleigh, North Carolina described the soil health implications from a 3-year transition period from field trials on three farms in North Carolina. Soil health was not altered much at all during the transition, as previous perennial pastures had already led to health soil conditions. This popular press report summarizes key results from a detailed scientific investigation reported elsewhere. Results can be used by farmers to improve pasture and livestock production during pasture renovations.
Nitrogen fertilizer, a common field production, inputs in agriculture is both necessary for achieving high productivity and threatens ecosystem integrity due to its easy transport to water bodies and emission to the atmosphere. An ARS scientist in Raleigh, North Carolina reviewed recent history of soil testing to predict soil nitrogen availability and summarized the last decade of research aimed at understanding how inherent soil nitrogen supply might supplement the need for nitrogen fertilizer inputs in corn and forage management systems. Laboratory incubations, greenhouse growth trials, and yield response trials from throughout North Carolina and Virginia provided clear evidence that soil-test biological activity can be considered a simple, rapid, and robust technique to estimate soil nitrogen availability. This new approach for adjusting nitrogen fertilizer recommendations will provide a sound scientific basis for more profitable crop and forage production, as well as reducing the negative consequences of agriculture on water quality and greenhouse gas emissions.
Soil carbon benefits the functioning of soil in many ways, and soil organic matter and its microbial residents impart vital ecosystem services on which we rely daily. An ARS scientist in Raleigh, North Carolina described the important processes influenced by soil carbon and the benefits imparted by soil to farmers and society. A summary of results from research stations across North Carolina were presented to exemplify how grassland management can be viewed as a key land use for sequestering soil carbon. Management of soil and soil organic matter is our duty. Humans depend on the orderly functioning of soil – driven in large part by the soil organisms that inhabit it. The brief primer on soil carbon and short essay on the value of soil to society continues a series of popular press articles aimed at informing farmers managing foraging and grazing lands in the US.
Roots give plants the structural footing to withstand the tempest wind and the pouring rain. An ARS scientist in Raleigh, North Carolina described how roots are the hidden half of the many products derived from forages. The rhizosphere has several orders of magnitude greater microbial biomass, potentially greater microbial diversity, and greater microbial activity than bulk soil. Daily life on the farm can be simply nurturing the complexity of soil life that masterfully abounds in the presence of a diversity of roots. This short essay on the functioning of roots and the rhizosphere continues a series of popular press articles aimed at farmers managing forage and grazing lands in the US.
Pastures are typically perennial forages that can change slowly over time. An ARS scientist in Raleigh, North Carolina described how soil nutrients and organic matter changed over the course of a dozen years of intensive management from a long-term field study. Requirement for lime with high inorganic nitrogen fertilization levels led to elevated calcium and magnesium levels. Grazing of forage and return of feces to the land led to increasing soil potassium while haying caused a decline in soil potassium due to forage removal. Soil phosphorus accumulated noticeably to 5-inch depth during the first 5 years when fertilized with poultry litter. Grazing pastures was highly beneficial for soil organic matter accumulation. Hay removal was placing carbon into a cattle diet elsewhere on the farm and not returning carbon contained in feces back to the hay ground. This summary of soil changes over time in perennial pastures continues a series of popular press articles aimed at farmers managing forage and grazing lands in the US.
Soil organic matter under perennial forages can change slowly over time. An ARS scientist in Raleigh, North Carolina described how organic matter changed over the course of several dozen years of pasture management from a diversity of on-farm trials conducted primarily in North Carolina and Virginia. Soil organic carbon and nitrogen both accumulated faster in the first 10 years of management than in the ensuing 40 years of management. Therefore, soil under forages could be considered a sink for carbon that otherwise accumulates in the atmosphere. Nitrogen is also stored in soil organic matter, acting as a reservoir for current and future needs to support pasture productivity. This summary of soil organic matter change over time in perennial pastures continues a series of popular press articles aimed at farmers managing forage and grazing lands in the US.
The following activities contributed to Objective 2 to characterize root-zone enrichment of soil organic matter and soil ecosystem properties of the region’s predominant agroecological farming systems.
Farmers are affecting soil organic matter with choice of land use. However, the extent of change in soil organic matter has not been adequately characterized. An ARS scientist in Raleigh, North Carolina described the results of sampling soils under conventional-till cropland, no-till cropland, grassland, and woodland on research stations across North Carolina. Soil organic carbon composes 58% of organic matter and nitrogen composed approximately 5%. Historical, pedogenic processes of soil formation contribute a large portion of natural organic matter in soils, but contemporary land use and management imparts equally strong effects on soil organic matter. These results summarize pedogenic and land use effects in four different physiographic regions of North Carolina. Results can be used by farmers and decision-makers to optimize soil carbon sequestration in the future.
Progress continued in our Objective 3 to screen diverse soybean germplasm for stress tolerance to elevated temperature and ozone air pollution. We screened soybean germplasm using our temperature gradient greenhouse (TGG) to assess responses to season-long elevated heat treatments (ambient +2°C and ambient +4°C relative to an unheated control) and open-top chambers (OTC) to assess response to elevated ozone treatments (80 ppb 12-hour mean relative to a charcoal-filtered control). Processing of yield samples and physiological data was completed for the summer 2023 trials to assess the heat and ozone stress responses of nine Glycine max x Glycine soja breeding lines developed by the USDA-ARS Soybean and Nitrogen Fixation Unit at Raleigh, North Carolina. These lines are unique germplasm representing potential sources of stress tolerance derived from wild soybeans for breeders to use in developing stress resilient cultivars. Summer 2024 TGG and OTC studies were initiated to test the stress responses of selected Soybean Nested Association Mapping (SoyNAM) parents. We will be looking for differences in heat stress and elevated ozone responses between SoyNAM parental lines and the common IA3023 parent used for development of the mapping populations. Parental lines with contrasting responses relative to IA3023 represent an opportunity to identify markers for heat or ozone stress response. Agreements with the United Soybean Board supported this research.
N16-7526, identified as a heat and ozone resilient soybean from our previous TGG and OTC screening trials, was planted with its heat and ozone sensitive parental line—Holladay cultivar—to conduct field trails in our field-based Air Exclusion System in the summer of 2023 and 2024. These two soybean lines were treated with separate and combined heat (ambient temperature + 3°C) and elevated ozone (80 ppb, 12-hour mean), charcoal-filtered air (15 ppb, 12-hour mean), and ambient air/temperature (experimental control). The environmental data and agronomic traits from 2023 demonstrated N16-7526 can tolerant both heat and ozone stresses, whereas the Holladay cultivar is sensitive to these stresses. These two soybean lines were planted in 2024 again to confirm these agronomic traits before releasing N16-7526 as a climate-smart soybean. Meanwhile, we will finish collecting plant physiological traits and plant, soil, and soil microbial materials from both 2023 and 2024 trials to study plant molecular and physiological regulations and plant and soil microbe interactions involved in heat and ozone stress tolerance and identify symbiotic soil microbes that help plants cope with these environmental stresses.
Accomplishments
1. Root-zone enrichment of soil organic carbon and nitrogen are improved under conservation land uses in Virginia. Grazing lands are considered an appropriate conservation land use that benefits both farmer and society due to erosion control, storage of soil carbon and nitrogen, and providing open space for wildlife habitat. Pastures are typically underappreciated despite a large potential to sequester carbon and nitrogen in soil that preserves environmental quality. An ARS scientist in Raleigh, North Carolina collected soil from 31 different farms in Virigina under grazing land, no-till cropland, and woodland. Results documented the large storage potential of grazing land compared with other land uses. Pasture age and stocking rate were critical factors influencing results, while stocking method, past fertilization, and low levels of hay feeding did not influence quantities of soil carbon and nitrogen. These results will be important for agricultural advisors, farmers, extension specialists, and scientists in the region to promote more efficient, carbon-storing practices for agriculture to simultaneously meet the production and environmental demands for a sustainable future.
2. Long-term ground-level ozone pollution disrupts plant-microbe-soil interactions in the agricultural ecosystem. Ozone pollution is a serious environmental threat to the US economy and its food security. Soybean, a major US staple crop, has an $18.7 billion export value, but ozone jeopardizes its annual production by 18%. Beyond its direct effects on crop production, ozone could impact agricultural ecosystems by its overall effect on plant health. However, this knowledge remains largely overlooked. To confront this environmental challenge by optimizing food sources as well as supporting robust agricultural ecosystems, the ARS Air Quality Research team in Raleigh, North Carolina employed two soybean variations with contrasting ozone sensitivity in a unique field-based ozone pollution simulation system under conventional field management practices. By applying machine learning technology and modelling algorithms to process large-scale soil microbial genomic data, plant physiological and agronomic traits, and soil health conditions, the ARS scientists summarized the carbon and nitrogen cycles in the soybean agricultural system and also pinpointed which symbiotic soil microbes enhance soybean resilience to ozone and which soil microbes deteriorate soil quality under ozone pollution. This study demonstrated that long-term ozone pollution profoundly degraded plant performance and soil health, alerting scientific experts and policy makers to a potential agroecosystem crisis. These findings highlight the urgent need for adaptive strategies against ozone damage to agricultural ecosystems and future food and economic losses.
3. Soil health and root-zone enrichment are greater under grassland than under paired cropland fields in the southeastern USA. Soil health conditions under privately managed grassland farms in the southeastern US has not received much attention. We hypothesized that beef cattle grazing on diverse composition of forage throughout their life cycle might lead to changes in meat quality compared with grain-finished beef. An ARS scientist in Raleigh, North Carolina collaborated with investigators from North Carolina State University and some presently at Utah State University to determine soil health conditions under grazed pastures compared with neighboring grain cropping fields in three different physiographic regions. Soil aggregation characteristics were greater under grazed pastures than cropland at all three locations. Soil chemical characteristics were variably affected by land use. Total organic carbon and nitrogen were greater under pasture than under cropland at two of the three locations. However, the biologically active fractions of carbon and nitrogen were greater under pasture than under cropland at all three locations. These results will be useful for farmers, agricultural advisors, and scientists to understand the benefits of well-managed grazing systems on productivity and environmental outcomes.
4. Soil aggregation and surface-soil properties are improved under grazed pastures and conservation land uses in Virginia. Water quality protection of the Chesapeake Bay continues to be a high priority in the Mid-Atlantic region. Nutrient runoff and sediment transport are key attributes that must be limited to further improve water quality. An ARS scientist in Raleigh, North Carolina collected soil from 31 different farms in Virigina under grazing lands, no-till croplands, and woodlands to assess soil aggregation and other soil-surface characteristics that indicate potential soil erosion and runoff. Grasslands were one of the best land uses for soil aggregation characteristics, equal to that of woodlands and greater than that of croplands. Of managed grasslands, pastures that were at least 10 years old led to the best soil aggregation, total soil N, and soil-test biological activity. Stocking rate was not definitive in its influence on surface-soil characteristics due to few observations at the lowest and highest rates. Most intensive rotational stocking led to reduced soil aggregation characteristics, but levels were generally high in all stocking methods. Pasture nitrogen fertilization was not always necessary to elevate soil conditions. These results will be important for agricultural advisors, farmers, extension specialists, and scientists in the region to promote more efficient, soil conserving practices for agriculture to protect water quality in the Chesapeake Bay and other surrounding watersheds.
5. Texture and organic matter are strongly associated with soil functional properties in crop and conservation land uses in North Carolina. Soil health evaluations may benefit from associations of simply determined metrics with more complicated properties and processes. Soil texture and organic matter are two overarching factors that control many other soil properties and, particularly, their susceptibility for change with conservation management. An ARS scientist in Raleigh, North Carolina evaluated the associations between soil physical, chemical, and biogeochemical properties and processes under conventional-till cropland, no-till cropland, grassland, and woodland across four physiographic regions in North Carolina. Both sand concentration and total soil nitrogen concentration formed strong associations with other soil properties. Sieved soil density was a strong integrative property of both sand and total soil nitrogen concentrations. Sieved soil density was a strong indicator of soil physical and biogeochemical conditions, including soil water and carbon storage. These results will be useful for scientists and agricultural advisors to help farmers understand the impacts of management on soil health conditions in the eastern US.
6. Integrated crop-livestock systems improve soil health, carbon sequestration, and agricultural resilience to overcome dangers of climate change. Industrialization of agriculture since World War II has resulted in simplification of biotic resources on farms, resulting in serious issues with resilience to pests, market vagaries, and climate change. More complex agricultural systems with integrated crop and livestock operations intertwined on farms or among farms could provide important benefits to build agricultural resilience. Two ARS scientists from Raleigh, North Carolina and Mandan, North Dakota collaborated to summarize recent research on integrated crop-livestock systems to address climate change issues. This effort was needed to help create more diverse and functional agricultural systems to meet production and environmental goals with the ongoing threats of climate change. This manuscript was invited as part of a special issue across journals of the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. This review and synthesis will benefit farmers, extension specialists, scientists, and policy makers to help create more resilient agricultural systems.
Review Publications
Agathokleous, E., Feng, Z., Frei, M., Jiao, S., Burkey, K.O. 2023. Response and adaptation of agricultural ecosystems to global changes. Agriculture, Ecosystems and Environment. 362. Article 108844. https://doi.org/10.1016/j.agee.2023.108844.
Franzluebbers, A.J., Hendrickson, J.R. 2024. Should we consider integrated crop-livestock systems for ecosystem services, carbon sequestration, and agricultural resilience to climate change? Agronomy Journal. 116:415-432. https://doi.org/10.1002/agj2.21520.
Franzluebbers, A.J. 2024. Characterizing soil Nitrogen availability to improve nitrogen fertilizer recommendations. Book Chapter. Chapter 12. http://dx.doi.org/10.19103/AS.2024.0135.16.
Franzluebbers, A.J., Van Vliet, S., Young, S., Poore, M.H. 2023. Soil health and root-zone enrichment characteristics between paired grassland and cropland fields in the southeastern USA. Grassland Research. 2(4):299-308. https://doi.org/10.1002/glr2.12066.
Zhang, K., Zentella Gomez, R., Burkey, K.O., Liao, H., Tisdale, R.H. 2024. Long-term tropospheric ozone pollution disrupts plant-microbe-soil interactions in the agroecosystem. Nature Communications. 30(3). Article e17215. https://doi.org/10.1111/gcb.17215.
Franzluebbers, A.J. 2024. Texture and organic matter associations with soil functional properties in crop and conservation land uses in North Carolina. Soil Science Society of America Journal. 88(2):449-464. https://doi.org/10.1002/saj2.20620.
Franzluebbers, A.J. 2024. Root-zone enrichment of soil organic carbon and nitrogen under grazing and other land uses in a humid-temperate region. Grass and Forage Science. 79(2):265-280. https://doi.org/10.1111/gfs.12665.
Franzluebbers, A.J. 2024. Soil aggregation and surface-soil properties under grazed pastures and conservation land uses in Virginia. Agronomy Journal. 116(4):1730-1745. https://doi.org/10.1002/agj2.21588.