Location: Plant Science Research2019 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 pasture-crop rotation experiment in Goldsboro, NC. 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. Research continues to evaluate genetic variation in ozone response of diverse soybean and wheat germplasm. ARS researchers have begun to develop evidence that ozone tolerance is associated with tolerance to other abiotic and biotic stress factors. In soybean, a leaf gas exchange trait associated with lower stomatal conductance in the Fiskeby III genotype appears to contribute to both ozone tolerance (through reduced ozone uptake into leaves) and drought stress tolerance (through reduced transpiration). In a continuing collaboration with a USDA-ARS soybean breeder, Fiskeby III has been used as a parent to develop agronomically adapted breeding lines that are now being tested for drought and ozone tolerance. In wheat, 43 leaf rust resistance genes expressed individually in a common genetic background were tested for ozone response. Specific genes were associated with enhanced ozone tolerance, suggesting a link between ozone tolerance and disease resistance. Soil microorganisms have profound effects on helping plants consume nutrients, as they trigger plant immune systems and ultimately promote plant growth. Plant root physiological and morphological changes are subject to environmental stresses, which may in turn influence under-ground ecosystems. However, the details of how environmental stresses like heat and elevated ozone levels that impact soil microbial abundance and compositions in crop habitats through altering root metabolisms are not well understood. In a comparison of root protein expression profiles in ozone sensitive and ozone tolerant genotypes, the expression level of 86 proteins were increased by elevated ozone in the ozone-sensitive variety, indicating these proteins are involved in ozone response. This included reduced cell elongation and root growth. In contrast, 46 proteins showed higher expression after elevated ozone treatment in ozone-tolerant genotypes, which may contribute to tolerance mechanisms. High resolution accurate mass spectrometry has been applied to identify those proteins. Meanwhile, soil microbiomes in rhizosphere from these ozone-contrasting genotypes were harvested to analyze the microbial community after elevated ozone treatment.
1. Soil-testing for nitrogen availability is effective in fall-stockpiled tall fescue pastures. Fertilization of perennial pastures with nitrogen may not always be cost-effective, due primarily to stored nitrogen in soil organic matter that can be released for plant uptake. Scientists from USDA-ARS in Raleigh, North Carolina, and at North Carolina State University evaluated tall fescue yield response to fall-stockpiled nitrogen application in a series of 55 field trials throughout Georgia, North Carolina, Virginia, and West Virginia. Yield response was either nil, modest, or high among various sites. Those sites predominantly with high soil-test biological activity and associated high nitrogen mineralization potential led to no yield response. Those sites with low soil-test biological activity and low nitrogen mineralization had high yield response. These results support the use of soil-test biological activity as an indicator of nitrogen availability so that producers can fine-tune nitrogen applications for greater production and profit, as well as to limit nitrogen losses to the environment. These results will be valuable for farmers, agricultural advisors, and applied agricultural scientists.
2. Soil-test biological activity is a key soil health indicator. Healthy soils are needed so that agriculture can continue to work for us by producing abundant food, feed, and fiber in the face of climate change and rising input costs. A key question these days is "how should we measure the health of soil?" Chemical, physical, and biological dimensions of soil health are important to consider. A seminal biological indicator is the breath of soil itself. Like us, soil is living and therefore breathes – the more it breathes, the more it needs to be fed – the more it is fed, the more work it can do. This review was prepared by a scientist at the USDA-ARS in Raleigh, North Carolina, to describe a test that creates a snapshot of how much a soil breathes for a short period following rewetting. Short-term carbon mineralization provides strong indications of (a) how well soil offers crops nitrogen from organic matter, a process called mineralization, (b) how soil becomes aggregated and able to filter and cycle water effectively in the environment, (c) providing readily utilizable substrates to support a diversity of soil microorganisms, and (d) the potential of soil to sequester C from the atmosphere, as well as store plant nutrients in slowly-accessible forms of soil organic matter. As an example, soil that has been fed a robust diet of crop diversity and kept intact with conservation tillage works hard to provide sufficient nitrogen to crops. In contrast, not knowing how much nitrogen is really available often leads to over-application of fertilizer and potential environmental degradation. This review summarizes some of the key findings from analysis of short-term carbon mineralization, also known as the flush of carbon dioxide, soil carbon dioxide burst, or soil-test biological activity.
3. Closing the global ozone yield gap – quantification and co-benefits for multi-stress tolerance. Ground level ozone is formed by the action of sunlight on volatile hydrocarbons and nitrogen oxides produced during combustion of carbon-based fuels. Although frequently considered an urban problem, ozone pollution is much broader in scope because weather systems transport the pollutants across long distances into agricultural areas. Ozone is toxic to plants, causing a reduction in the growth and yield of sensitive crops. An international group of scientists from organizations in the United Kingdom, Norway, Sweden, Germany, China, Japan, India, and USDA-ARS in the Raleigh, North Carolina, worked as a team to model the impact of ozone on yield losses for soybean, wheat, maize, and rice on an annual basis world-wide. The highest ozone-induced production losses for soybean are in North and South America whilst for wheat they are in India and China, for rice in parts of India, Bangladesh, China and Indonesia, and for maize in China and the USA. The analysis also showed the same areas are often at risk of high losses from pests and diseases, heat stress and to a lesser extent aridity and nutrient stress. Management practices to reduce the ozone impacts and breeding approaches to improve the ozone tolerance of crops are potential solutions to reduce the impact of ozone. Given the severity of ozone effects on staple food crops in areas of the world that are also challenged by other stresses, we recommend increased attention to the benefits that could be gained from addressing the ozone yield gap.
4. Modeling the effects of tropospheric ozone on wheat growth and yield. Ground level ozone is formed by the action of sunlight on volatile hydrocarbons and nitrogen oxides produced during combustion of carbon-based fuels. Although frequently considered an urban problem, ozone pollution is much broader in scope because weather systems transport the pollutants across long distances into agricultural areas. Ozone is toxic to plants, reducing the growth and yield of sensitive crops including wheat. Crop modelers at the University of Florida incorporated the effects of ozone into the DSSAT-NWheat crop model. The model reproduced the results from an ozone field trial conducted at Raleigh, North Carolina, by scientists from USDA-ARS and North Carolina State University. The modified NWheat model simulates the effects of ozone stress on wheat growth and yield and interactions with other growth factors and can be used to estimate impacts of climate change and air pollution on wheat production.
5. Interaction of carbon dioxide enrichment and reactive nitrogen stimulate soil cation losses and acidification. Carbon dioxide is a well known greenhouse gas, and rising carbon dioxide in the atmosphere is expected to enhance plant growth through higher rates of photosynthesis. However, indirect effects of elevated carbon dioxide on complex terrestrial ecosystems is much less understood. A collaboration of North Carolina State University, USDA-ARS at Raleigh, North Carolina, and Chinese colleagues showed that elevated carbon dioxide can cause soil acidification with a concomitant loss of nutrient cations. Application of inorganic nitrogen fertilizers enhances this effect. A mechanism linking atmospheric carbon dioxide with plant and soil microbial processes was developed to explain this phenomenon. This demonstration of elevated carbon dioxide enhancement of soil acidity raises the possibility that rising carbon dioxide could inhibit future crop and forest productivity through loss of critical soil nutrients required for plant growth, a critical consideration in modelling future climate impacts.
6. Contrasting effects of warming and ozone on soil nitrous oxide emissions. Nitrous oxide is a potent greenhouse gas with a global warming potential 300 times greater than that of carbon dioxide, and is a factor in the depletion of the stratospheric ozone that shields the earth from ultraviolet light. Globally, agricultural soils are a major source of nitrous oxide from microbial processes associated with the use of manure and chemical fertilizers. A team of scientists from Nanjing Agricultural University (China), North Carolina State University, and USDA-ARS at Raleigh, North Carolina, showed that climate change factors impact nitrous oxide production through effects on the soil microbes. In a field study with soybean, season-long elevated temperature treatment stimulated nitrous oxide emission and the soil microbes associated with nitrous oxide production. In contrast, elevated ozone had no significant effect on nitrous oxide production. Together, these findings show that climate change may alter nitrous oxide production from agricultural systems, a critical consideration in modelling future climate impacts.
7. Soil organic matter fractions were not affected by stocking method in the medium-term. Rotational stocking of pastures has received renewed attention as a potential strategy to support a more ecologically based grazing management approach. Soil health data to support the approach has been lacking. Therefore, a team of USDA ARS scientists in El Reno, Oklahoma, collaborated with an ARS scientist in Raleigh, North Carolina, to determine how continuous and rotational stocking affected soil organic matter and soil biological activity over the course of 8 years in a field-scale study at the Grazinglands Research Laboratory in El Reno, Oklahoma. Soil carbon and nitrogen fractions were not affected by stocking method – neither positively nor negatively. All properties were highly stratified with depth, meaning that soil organic matter was most concentrated near the surface and declined with greater depth in the profile. The combination of abundant available nitrogen from high mineralization potential and lack of nitrification to nitrate led us to postulate that nitrogen could be effectively conserved in this grazed remnant prairie ecosystem. This information will be valuable for farmers and extension agents to design robust and resilient grazing management systems.
8. Crop productivity and soil carbon potentially enhanced with pasture-crop rotations. Specialization of agricultural operations and commodities in many developed countries of the world during the last half century has led to large production gains, but often at the expense of environmental quality and socio-economic disruption. Soil organic carbon is a key indicator of soil health that is low with contemporary clean-cultivated specialized crop production practices and high when farms are managed with conservation tillage, cover crops, manure application, and diverse rotations, especially multi-year pasture-crop rotations. A scientist with USDA Agricultural Research Service in Raleigh, North Carolina, collaborated with a scientist from the National Institute of Agricultural Research in Lusignan, France, to review literature and describe some of the environmental and social changes expected when re-integrating forages in rotation and grazing livestock with traditional row crops in temperate environments. Our thesis was that integrating pastures and crops with other ecologically based practices will lead to dramatic improvement in soil organic carbon and nitrogen contents so that long-term fertility can be restored and environmental quality can be significantly improved to meet the challenges for greater quantity and quality of food production, sustenance of human health, maintenance of wildlife diversity, and balancing our human footprint with Nature’s capacity to serve our needs.
9. Bradyrhizobium inoculation and molybdenum application enhance peanut production in pasture-crop rotations. Resource-efficient crop production requires that soil biological components be at peak capabilities to transform nutrients and make effective use of embedded investments in field production. Peanut is an important grain legume dependent on biological nitrogen fixation to be most efficient in producing sufficient quantity and quality of high-protein product. A scientist at USDA-ARS in Raleigh, North Carolina, collaborated with scientists at Sao Paulo State University to study the impacts of legume inoculation with Bradyrhizobium and application of molybdenum to stimulate the nitrogen-fixing enzymatic process on a soil that had been under long-term pasture in the Cerrado of Brazil. Activity of the nitrogen-fixing enzyme was greatest two months after plant emergence when inoculated and fertilized at high molybdenum rate. Number of pods per plant was the yield component that most directly influenced pod and kernel yield in the treatments with inoculation. In agricultural areas with pasture for several years, Bradyrhizobium inoculation and molybdenum fertilization with at least 0.75 ounce per acre increased yield of pods and kernel in a no-tillage system with large quantity of surface straw. These results will be useful to farmers and extension specialists in sub-tropical environments to increase the sustainability of low-resource-input farming systems.
10. Nitrogen on cover crops in association with soybean can be managed for sustainability in the tropics. Enhancing productivity and maintaining soil and water resources are two important goals of agricultural sustainability in agricultural expansion areas around the world. Optimizing soybean production while minimizing soil loss from erosion are concerns in Brazil and other tropical and sub-tropical regions. A scientist at USDA-ARS in Raleigh, North Carolina, collaborated with scientists at Sao Paulo State University to study the impacts of nitrogen fertilization of grass cover crops prior to soybean production on straw nutrient content and soybean grain production. Nutrient content of cover crop straw was enhanced due to greater biomass production in treatments with nitrogen applied 20 and 10 days before desiccation. Soybean grain yield was greater following Urochloa brizantha than following Urochloa ruziziensis. Nitrogen application at different times did not affect soybean grain yield. These results suggest that Urochloa biomass and nutrient cycling can be enhanced with nitrogen application, but it had little short-term impact on soybean yield components. These results will be useful for farmers and agricultural advisors to design more efficient conservation agricultural systems for the tropics and subtropics.
11. Proverbs describing our relationship with soil shared internationally. The International Union of Soil Sciences is assembling information to celebrate the United Nations Declaration of the Decade of Soil – 2015-2024. One of the projects is to assemble a book of country-specific local knowledge pertaining to soil and its management. ARS scientist at Raleigh, North Carolina, prepared a short description of several indigenous proverbs pertinent to land care and the environment. This chapter describes indigenous passages offering advice to steward the land.
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Zhang, L., Qiu, Cheng, L., Wang, Y., Liu, L., Tu, C., Bowman, D., Burkey, K.O., Bian, X., Zhang, W., Hu, S. 2018. Atmospheric CO2 enrichment and reactive nitrogen inputs interactively stimulate soil cation losses and acidification. Environmental Science and Technology. 52:6895-6902.
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Mills, G., Sharps, K., Simpson, D., Pleijel, H., Frei, M., Burkey, K.O., Emberson, L., Uddling, J., Broberg, M., Feng, Z., Kobayashi, K., Agrawal, M. 2018. Closing the global ozone yield gap: Quantification and co-benefits for multi-stress tolerance. Global Change Biology. 24:4869-4893.
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Abdallah, A., Mashaheet, A., Zobel, R., Burkey, K.O. 2019. Physiological basis for controlling water consumption by two snap beans genotypes using different anti-transpirants. Agricultural Water Management. 314:17-27.
Xu, S., He, X., Burkey, K.O., Chen, W., Li, P., Li, Y., Li, B. 2019. Ethylenediurea (EDU) pretreatment alleviated the adverse effects of elevated O3 on Populus alba ‘Berolinensis’ in an urban area. Journal of Environmental Science. 84:42-50.
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Franzluebbers, A.J. 2018. Soil proverbs in the United States of America. In: Global Soil Proverbs: Cultural Language of the Soil. Chapter 28, pgs 205-207.
Tanaka, K., Crusciol, C.A., Soratto, R.P., Momesso, L., Martins De Costa, C.H., Franzluebbers, A.J., Junior, A.O., Calonego, J.C. 2019. Nutrients released by Urochloa cover crop prior to soybean production. Nutrient Cycling in Agroecosystems. 113:267-281.
Franzluebbers, A.J., Gastal, F. 2018. Building agricultural resilience with conservation pasture-crop rotations. In: Agroecosystem Diversity: Reconciling Contemporary Agriculture and Environmental Quality. Chapter 7, pgs 109-121.