Brief Summary of Minutes of Annual Meeting

The meeting opened with remarks and introductions by all in attendance. USDA representatives Mat Ngouajio and Mac Bisoondat followed with remarks on behalf of the USDA and opened the floor to questions.  Objective leads for objectives 1-5 delivered prepared reports to summarize activities, accomplishments, and impacts.  An open discussion followed with some remarks concerning what might be improved upon moving forward.  Next steps include an in-person meeting for the renewed project in Gainesville, FL, on January 8, 2025. Voting will need to take place to fill vice-chair and secretary roles.    

Objective 1: Identify a common set of biological and economic measures that can be applied across crop and cover crop combinations throughout the region to generate a region-wide database.

5/7 (according to completed outline sections) of a review article on soil health indices appropriate and applicable to the Southeastern U.S.A. has been drafted with 3 authors. The paper covers biological, physical, and chemical indices of soil health.  Evaluations of individual indices have resulted in reduced reliance on non-predictive measures such as permanganate oxidizable carbon, total organic carbon, PLFA, and others.  In drier sandy soils of the region, dry aggregate stability has been identified as more useful than wet aggregate stability as an indicator of soil aggregate formation.

Several proposals have resulted in funding awards to support this objective.

USDA-NIFA OREI (FAIN # 20235130040849) “Fostering sustainable organic cotton production in the US through research and outreach on organic regenerative practices.  TX, TN

USDA-NIFA SAS (FAIN # 20246801241750) “AFRI: Climate-Smart Cotton: Developing Precision Regenerative Practices and Market Opportunities for Addressing Climate Change in the Cotton Belt”. NC State, GA, AL, MS, TX

USDA-NIFA OREI (FAIN # 20235130040913) “Onion-IQ (Improve Quality): Improving quality, resilience, soil health and food safety in organic onion in the southeastern and southwestern U.S.” GA, TX

Objective 2:  Select and evaluate summer and winter cover crop germplasm for regional adaptability and determine the appropriate timing of planting, seeding rates, utilization of cover crop goods (includes grazing), and termination to optimize benefits without adversely affecting cash crop cycles.

A coordinated field experiment was conducted across states in the southern United States, representing 16 site-years in Alabama, Arkansas, Kentucky, North Carolina, Tennessee, Texas, Louisiana, Maryland, and Georgia, during the 2019-2020 and 2021-2022 winter cover crop growing seasons. The experimental design was a randomized strip-plot design with two blocks per site. The whole plot factors included 1) four legumes seeding rates and 2) five legume species; a fully-factorial combination of these levels was applied to one plot in each block. Seeding rate levels were based on the drilled recommended seeding rates (RSR) in Clark (2007) for each species and included “full” (RSR), “high” (150% of RSR), “low” (50% of RSR), and “lowest” (25% of RSR). Species of legume cover crops included hairy vetch (‘AU Merit’), crimson clover (‘Dixie’), winter pea (‘Wyo’), common vetch (VNS), and berseem clover (‘Frosty’). Cereal rye (‘Wrens Abruzzi’) inclusion (with vs. without) was applied as a strip plot factor. Cereal rye was planted as a mixture with leguminous cover crop treatments as a strip across each block at a seeding rate of 33.6 kg ha-1. Strips were randomly assigned to one side of the block or the other. Planting and termination dates were chosen at each site based on local recommendations and planned subsequent cash crops.

Before termination of the cover crop, biomass samples were taken by clipping all aboveground plant tissue near the soil surface from one randomly placed 0.25-m2 quadrat per plot. Biomass samples were dried until constant mass was reached, then the dry weight was recorded. Legume and cereal rye biomass from the mixture plots were partitioned prior to drying and weighing for 13 of the 16 site-years (AL_1, AL_2, AR_2, GA_1, GA_2, KY_1, KY_2, LA_1, MD_1, MD_2, NC_2, TN_1, and TX_1). Weed biomass was also partitioned prior to drying and weighing for 8 site-years (AL_2, AR_2, GA_2, KY_1, MD_2, KY_2, LA_1, and TN_1) in which appreciable weed biomass was present.

Results from this manuscript are in preparation and will be submitted for peer-review in October 2024. Preliminary results indicate that for the range of seeding rates tested, no significant impact of seeding rate on monoculture legume biomass was observed. Across locations, crimson clover and hairy vetch produced greater cover crop biomass compared to berseem clover and common vetch when planted as monocultures. Incorporating cereal rye in a mixture with a legume cover crop increased total biomass compared to legume cover crop monocultures (Figure 3). These findings broadly support the use of lower legume seeding rates for producers in the southern region who are interested solely in aboveground biomass production. While lower seeding rates would reduce input costs, provisioning of other ecosystem services (including groundcover and N fixation) should be evaluated as well.

Objective 3: Assess the influence of cover crops on soil moisture, nutrient cycling, and soil microbiology.

The team has made significant progress in advancing the research efforts tied to Objective 3. Ongoing experiments across participating states are investigating the effects of cover crops on several critical factors, including soil moisture retention, nutrient cycling, and soil microbiology. These studies are helping to uncover valuable data on how cover crops contribute to sustainable agricultural practices. A number of graduate students are engaged in these projects, conducting fieldwork and data analysis, which is expanding the body of knowledge around these topics.

To support the long-term goals of Objective 3, team members are also actively pursuing external funding. Grant proposals have been submitted to expand the research and further investigate the intersections between cover crops, soil health, and crop productivity. These efforts are aimed at addressing both immediate project needs and expanding the research scope to include new variables and long-term outcomes.

Multi state studies have been conducted via the research committee of the SCCC to evaluate Brassicas, Legumes, and Cereals species prior to summer cash crops.  Nitrogen release in 2023 was found to range from -5 lbs acre-1 for cereals such as triticale, cereal rye, and oat to 97 lbs acre-1 for legumes such as crimson clover and 42 lbs acre-1 for hairy vetch.  In 2024, N release was similar, with -8 to -9 lbs acre-1 observed in cereal rye and oat.  Legumes released as much as 56 lbs acre-1 for crimson clover and 81 lbs for hairy vetch.

A study in Texas and Mississippi evaluated the possibility of sowing cover crops on ridge tilled fields.  The outcomes suggest that establishment is possible without detrimental effects to soybean yield.  Also broadcasting prior to hipping resulted in more emergence on beds than in between in the furrows.

Objective 4:  Characterize cover crop efficacy for enhancing cropping system resilience to weeds, pests, and plant pathogens.

A multistate assessment of cowpea cover crop germplasm has been completed.  A draft manuscript is completed summarizing this work.  Shoot biomass and weed biomass were evaluated for three germplasm lines across 8 states.  Seeding rate was evaluated with positive relationships between rate and shoot biomass and negative relationships derived between rate and weed biomass.  A summary of this work was already presented at the WSSA WSWS 2023 meetings.

https://wssa.net/wp-content/uploads/WSSA-WSWS-2023-Proceedings.html.

A multistate on farm experiment lead by Dr. Treadwell was summarized at the annual meeting of the Florida State Horticultural Society.

The common experiment funded under the SAS CAP Grant evaluated soybean, cereal rye, corn rotations in multiple states.  Terminate date for the cover crops was the primary evaluation goal.  Weed biomass was negatively related to rye biomass and termination date.  However, corn yield was also negatively related to the same factors.  Publications from this work are pending.

Objective 5:  Generate an economic database that researchers, technical advisors, and farmers can use to assess the short and long-term economic outcomes of cover crop use.

Dr. Ruiz-Menjivar and team members in his lab “Sustainable Development and Socio-economic Resilience Lab” (SDSR) completed a bibliometric review of the existing literature

related to the environmental impacts of cover crops (CC) on agricultural production. The team--including a doctoral student, a research intern, and a professor in the UF Geography department—retrieved and analyzed 3246 peer-reviewed articles published in the last forty years from one of the major academic research databases, Web of Science. The results of this project were published in a Review in the Environments Journal.

Our findings showed that the number of peer-reviewed outputs documenting the effects of CC on the environment—particularly the relationship between the use of CC and soil properties—has consistently increased in the past 40 years, with a notable rise in publications within the last decade. Research studies have primarily addressed 18 core research topics, where the most salient domains included the impact of using winter CC in cropping systems, the relationship between CC usage and nitrous oxide emissions, reduction of nitrate leaching in agroecosystems, and the implications of incorporating CC and reduce tillage/no-tillage for soil health and field quality. Particularly, we identified three main sequential stages of published research. In Stage 1 (Years: 1980–2000), research mainly examined the association between CC, nitrogen management, and weed suppression. In Stage 2 (Years: 2001–2010), our findings showed that CC studies assessed the impact of using different CC mixtures in farming systems. In Stage 3 (Years: 2010–2021), the literature primarily addressed the environmental benefits of CC, particularly the implications for physical and chemical soil properties and soil health indicators to assess the impact of CC. The countries with the most research outputs were the United States, Brazil, and Spain. Finally, the majority of top contributing institutions to the field of CC research were based in the United States. USDA-ARS was the most productive contributor to the literature on CC research in the last forty years.

The need for longer periods of record for research is directly tied to the need for greater emphasis on soil health. More data for longer observation periods are needed to identify critical parameters in the many systems of CC/cash crop combinations, all subject to variance in soil physical characteristics. Growers have also expressed interest in larger-scale trails that directly compare a farmer’s current practices and systems using CC to assess the total variance in field conditions, perhaps plots as large as 20 acres. Experienced farmers also argue that there is an over-emphasis on yield and insufficient attention to profitability. The basic argument is that a farmer can earn a higher profit per unit of production with fewer inputs because the cost of the inputs is higher than the value of the added productivity. This is an economic factor that deserves attention, given the rapidly increasing cost of fertilizer inputs and the instability in yield that we may anticipate under the conditions of global climate change.

Govindasamy, Prabhu, Senthilkumar K. Muthusamy, Muthukumar Bagavathiannan, Jake Mowrer, Prasanth Tej Kumar Jagannadham, Aniruddha Maity, Hanamant M. Halli et al. "Nitrogen use efficiency—a key to enhance crop productivity under a changing climate." Frontiers in Plant Science 14 (2023): 1121073.

Liu, Y., Ruiz-Menjivar, J., Hu, Y., Zavala, M., & Swisher, M. E. (2022). Knowledge mapping of the extant literature on the environmental impacts of using cover crops—a scientometric study. Environments, 9(9), 120.

Johnson, A.M., Gamble, A.V., K.S. Balkcom, and N.R. Hull. 2021. Influence of Cover Crop Mixtures on Soil Health in Southeastern Crop Production Systems. Agrosystems, Geosciences & Environment. 4:3 doi:10.1002/agg2.20202

Meeks, C., Cabrera, M., Thapa, R., Noor, N., Mirsky, S., & Reberg‐Horton, C. (2023). Biochemical composition of cover crop residues determines water retention and rewetting characteristics. Agronomy Journal, 115(6), 3173-3187.

Salehin, S. M. U., Rajan, N., Mowrer, J., Casey, K. D., Somenahally, A. C., & Bagavathiannan, M. (2024). Greenhouse gas emissions during decomposition of cover crops and poultry litter with simulated tillage in 90‐day soil incubations. Soil Science Society of America Journal, 88(5), 1870-1890.

Kumari, A., Gamble, A. V., Seehaver, S., Pettit, A., Shadow, A., McWhirt, A., Carr, B., Chase, C. A., Reberg-Horton, C., Kidwellslak, D., Haramoto, E., Fultz, L., Basinger, N. T., Barrett, R., Mirsky, S. B., & Sykes, V. R. (2023) Southern Cover Crops Council Multi-State Trials: Winter Annual Legume Cover Crop Species Selection and Seeding Rates for the South [Abstract]. ASA, CSSA, SSSA International Annual Meeting, St. Louis, MO. https://scisoc.confex.com/scisoc/2023am/meetingapp.cgi/Paper/152008

Matthiesen, R., Adam, J., Bagavathiannan, M., Basche, A., Boakye, D. A., Chase, C. A., ... & Robertson, A. E. (2023, October). Effect of Winter Cereal Rye Biomass on Corn Seedling Disease across 16 Locations in the United States. In ASA, CSSA, SSSA International Annual Meeting. ASA-CSSA-SSSA.