Location: Plant Science Research2022 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.
In support of Objective 1, soil and plant analyses continue to be determined by ARS scientists at Raleigh, North Carolina from long-term projects, including an agroforestry project under silvopasture management and a farming systems experiment in Goldsboro, North Carolina. A 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. Roots support plant fitness by absorbing nutrients and water and interacting with soil microorganisms and their environment. Therefore, root traits play fundamental roles in determining plant health and productivity. However, how roots respond to environmental stress is often overlooked. Global warming has significantly impacted agriculture in the southeastern area of the United States. Even so, the knowledge of how heat affects southeastern wheat crops is limited. Under Objective 3, we tried to understand how heat alters root structure and identify root heat-tolerance traits in wheat to improve crop breeding programs. We analyzed heat tolerance in corresponding root structures for hard red winter wheat cultivars by using our recently established Temperature Gradient Greenhouse. Our research revealed that rising temperatures (+2 and +4 degrees Celsius above ambient) decrease wheat yield wheat by 15% to 40%. The subsequent ranking of heat resistance among our experimental cultivars was: ‘Turkey’ > ‘Catawba’ > ‘NuEast’ > ‘Pioneer 25R46‘> ‘Hilliard’. Root analyses demonstrated that the heat resistance was associated with increased fine roots and high ratios of shoots to roots. These heat-tolerant root traits will help breeders generate global warming-resistant wheat. Ground-level ozone is the most harmful greenhouse gas and directly damages plant growth and productivity by negatively affecting photosynthesis and carbon deposition to soil. Soil microbial diversity, community networks, and function play vital roles in improving plant health under environmental stresses by providing nutrients to plants. To understand how ozone impacts soil microbes and identify beneficial soil microbes improving ozone resistance in plants, we analyzed soil microbial diversity and networks associated with the ozone-resistant soybean cultivar ‘Jake’. Our results demonstrated that soil fungi were more sensitive than bacteria to elevated ozone and that bacterial taxa could contribute to nitrogen (Chloroflexales) and carbon (Caldilineales and Thermomicrobiales) acquisition to support ozone resilience in ‘Jake’. In support of Objective 3a, screening of soybean and wheat germplasm for heat stress tolerance was continued. Our custom-built Temperature Gradient Greenhouse that provides elevated temperature treatments of +2 and +4 degrees Celsius above ambient conditions (the range of projected climate warming in the 21st century) is being used to screen germplasm of soybean and small grains. Significant genetic variation in yield response to elevated temperature was found for barley, soybean, and wheat. Overall, small grains were more sensitive to rising temperature than soybeans. For two barley genotypes tested, yield losses of 20 to 60% were observed in the +2 Celsius treatment with higher losses of 35 to 80% in the +4 Celsius treatment. For nine wheat genotypes tested, yield losses of 15 to 40% were observed in both the +2 and +4 Celsius treatments. For sixteen soybean genotypes tested, yield responses ranged from a 50% yield stimulation to a yield loss of 30% in the +2 Celsius treatment and ranged from a 10% yield stimulation to a yield loss of 40% in the +4 Celsius treatment. This in-house objective was supported by grant funding from the United Soybean Board. In support of Objective 3b, screening of soybean germplasm for drought stress and ozone tolerance was continued. Open-top chambers are being used to assess water use efficiency (a drought tolerance leaf trait) and ozone yield response of drought-tolerant breeding lines developed by soybean breeders in the Midwest and Southeast. Breeding lines derived from Fiskeby III as the drought tolerant parent exhibited greater water use efficiency than the check cultivar while the other breeding lines appeared to derive drought tolerance from other traits. Yield data are being developed to determine if drought tolerance is linked to ozone tolerance. This in-house objective was also supported by grant funding from the United Soybean Board.
1. Root-zone enrichment of soil organic carbon determined under cotton production systems. ARS scientists at Raleigh, North Carolina believe soils in the southeastern United States have 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 accumulation of soil organic matter with adoption of conservation tillage technologies on 120 cotton farms throughout North Carolina. Significant sequestration of organic carbon was determined on those fields with adoption of continuous conservation tillage (i.e., no tillage or strip tillage). When conservation tillage was rotated with disk tillage due to the needs of other crops in rotation with cotton, sequestration of organic matter was reduced. This study clearly shows potential for significant soil organic carbon sequestration, as well as total soil nitrogen and soil-test biological activity, when conservation tillage practices are deployed continuously throughout the crop rotation. These results will be useful for scientists, agricultural advisors, and farmers to develop better conservation strategies to improve the quality of soils in the cotton growing region of North Carolina and beyond.
2. Climate change factors limit carbon sequestration. Climate change consists of multiple interacting components including rising temperatures and increased air pollutants such as ozone. These factors directly impact plant growth and crop yields. However, much less is understood about the effects of temperature and ozone in the larger agroecosystem, particularly at the root-soil interface where carbon cycles and carbon sequestration are regulated. A collaboration of North Carolina State University scientists, ARS scientists at Raleigh, North Carolina, and Chinese colleagues showed that elevated temperature, elevated ozone, and the combination all reduce soybean root biomass, reduce root interactions with beneficial fungi, and favor the formation of fine roots. The overall effect was stimulation of organic carbon decomposition. These findings suggest that rising temperature and elevated ozone pollution may reduce the capacity of soils to sequester carbon. These results will be important to researchers, modelers, and policy makers in predicting the capacity of agricultural management systems to accumulate soil carbon.
3. Conservation tillage and cover cropping effects on soil in the southeastern US reviewed. Conservation agricultural systems can be effective at improving soil health in the southeastern United States. However, how such systems perform across a diversity of soil and environmental conditions has not been thoroughly evaluated. A scientist from ARS Raleigh, North Carolina, collaborated with investigators from Clemson University to review literature and assemble on-farm data to assess soil health conditions across a diversity of environments in South Carolina, North Carolina, and Virginia. Both recent literature and on-farm trial data suggested significant improvement in both soil organic carbon and nitrogen fractions and inorganic nutrients with adoption of no tillage and cover cropping. Evidence was strong for soil health improvement with adoption of no tillage compared with inversion tillage, and evidence was good but not universal across physiographic regions or soil property for soil health improvement with addition of cover crops to the no tillage system. Evidence was weakest for soil health improvement with multi-species cover cropping compared with single-species cover cropping. The large number of fields sampled allowed us to establish a first estimate of optimal soil health conditions using a survey approach with probabilities. We suggest that additional on-farm research with consistent soil-test methodologies will be useful for further optimization of soil health on farms in the southeastern US. This research will help researchers, agronomic advisors, and farmers to better assess agricultural management in the region.
4. Soil-test biological activity predicts soil nitrogen availability in forage systems. Soil testing for nitrogen availability in pasture systems would benefit from a rapid and reliable indicator to assess nitrogen availability. An ARS scientist at Raleigh, North Carolina, and John Hopkins University (formerly at North Carolina State University) evaluated the plant growth responses of a test crop planted in unamended soils collected from 55 pastures throughout North Carolina and Virginia. Plant dry matter and nitrogen uptake of the test crop during six weeks of growth in the greenhouse was highly related to several organic carbon and nitrogen fractions. However, a simple, rapid, and reliable indicator based on simple microbial activity (the flush of carbon dioxide) was best associated with plant growth responses. Low cost and short time required for this simple indicator make it suitable for soil testing, and because it was robust in predicting plant growth. The strong association of the flush of carbon dioxide with plant nitrogen uptake under semi-controlled greenhouse conditions corroborated use of the assay as a rapid and reliable indicator of soil nitrogen availability. These results will be valuable for farmers wanting to make efficient applications of nitrogen to enhance profit and steward natural resources.
5. Soil aggregation is improved with conservation tillage under cotton production. Soil aggregation is an important physical indicator of soil health. Cotton in North Carolina is typically produced on low-sloping, sandy soils that may still be eroded by intense precipitation during summer and strong winds from exposed soil in the spring. An ARS scientist at Raleigh, North Carolina, collected soil from 120 cotton fields to determine the extent of soil aggregation in response to dominant tillage management deployed. Although sandy soils do not have a strong propensity to physically aggregate, significant aggregation was still observed and became increasingly important in soils with greater proportion of clay- and silt-sized particles mixed with the dominant sand-sized fraction. Continuous conservation tillage was important to increase soil aggregation compared with frequent disk tillage. On those farms with conservation tillage for cotton production rotated with disk tillage for other crops, soil aggregation was more similar to that of frequent disk tillage than that of conservation tillage. These results will be important for farmers and agricultural advisers to make soil health management decisions to specifically address soil erosion and surface sealing.
6. Optimum soil water content determined for diversity of soils for biological testing. Manipulations of soil in the laboratory for determining soil biological activity need to effectively address soil water content when comparing a diversity of soil types from around the world. Soil water content at optimum moisture must be balanced with equal portions of air, i.e., 50% water-filled pore space. An ARS scientist at Raleigh, North Carolina, determined soil water content of >250 soils varying in soil organic matter and texture from throughout the United States, as well as some soils from Canada, Guam, and Brazil. Gravimetric soil water content at 50% water-filled pore space (i.e., optimum for soil microbial activity) could be defined at 58% of water held at near saturation or at 69% of water held at water-holding capacity. Drying soil at 55°C rather than at the standard soil drying temperature of 105°C was a small bias with 1% of water retained, but it allowed samples to be handled in the laboratory without negatively affecting soil microbial activity. The results of this study will be useful for other research soil scientists and commercial soil testing facilities to better determine soil-test biological activity to assess soil health condition based on management in the field.
7. Root-zone enrichment concept validated with literature data. Estimation of soil organic carbon sequestration has traditionally involved resource-intensive, long-term field studies under controlled conditions. A new approach was proposed by an ARS scientist at Raleigh, North Carolina. This approach was based on soil-profile distribution of soil organic carbon concentration and assuming that the carbon concentration at 12-inch depth could be used as a reference point for each individual soil pedon. Published literature from 52 studies was collected and soil organic carbon data analyzed from a total of 423 management units. No tillage compared with conventional plow and/or disk tillage led to significantly greater storage of soil organic carbon in the surface 12 inches of soil. Sequestration estimates were similar under grassland management as with no-till cropland but were even greater with woodland management. Available evidence suggests that soil organic carbon sequestration may not be different across different regions, but the inherent level of soil organic carbon at 12-inch depth may be different due to pedogenic conditions. This information will help famers, agricultural advisers, and policy makers understand how conservation agriculture changes the physical environment of the soil.
8. Evidence is weak for deep soil-profile accumulation of carbon with no tillage. Can significant amounts of soil organic carbon be stored below the surface foot of soil under conservation agricultural approaches? This was the question posed in a review of literature by ARS scientists at Raleigh, North Carolina. Published literature from three dozen studies was collected and soil organic carbon data analyzed from a total of 71 direct comparisons (more than one comparison in each study due to different cropping systems and/or management approaches tested). The evidence was clear that no tillage compared with conventional plow and/or disk tillage led to significantly greater storages of soil organic carbon in the surface 4 to 8 inches of soil. However, many studies showed that no tillage had less soil organic carbon in lower depths to about 2 feet. On balance over the whole profile to 2-foot depth, soil organic carbon was sometimes greater under no tillage than conventional tillage and more often not different between no tillage and conventional tillage. Available evidence suggests that soil organic carbon is not sequestered below the plow layer to any greater extent under no tillage than under conventional tillage, and more typically, is lower under no tillage than under conventional tillage in the 1-to-2-foot depth of the soil profile. This information will help famers, agricultural advisers, and policy makers understand how conservation agriculture changes the physical environment of the soil.
9. Fertilization has significant carryover benefit to cropping in Brazil. Cycling of nutrients in diverse cropping systems can become more efficient with better understanding of the temporal changes that occur. An ARS scientists at Raleigh, North Carolina collaborated with scientists from the Federal Technical University of Parana in Brazil to determine impacts of how nitrogen fertilizer and rotation of grazed cover crops with corn affected nitrogen, phosphorus, and potassium nutrition of corn. Nitrogen supplied to winter cover crop was carried over to the corn crop, effectively reducing the nitrogen fertilizer requirement of corn. Phosphorus nutrition was adequate when the winter cover crop was not fertilized with nitrogen, owing to reduced biological demand on soil phosphorus. System-level nitrogen fertilization strategies could be developed to help farmers become more efficient in resource utilization and economic return.
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