Final report for GS23-289
Project Information
The growing demand for organic agricultural products has led to increased interest in adopting organic farming practices. Double-cropping, wherein two crops are grown sequentially within one year, offers a promising approach to improve resource use efficiency and productivity, especially in the southeast US which experiences a long growing season. This study aims to evaluate the successful establishment of organic double-crop soybean following wheat harvest in the southeastern USA and to compare the agronomic and ecological benefits with a full-season soybean. The research objectives are: (1) to examine the effect of reduced tillage and no-tillage practices on the establishment, growth, and productivity of full-season soybean and a wheat-soybean double-crop in an organic system; and (2) to identify the best cultural practices for a successful wheat-soybean double-crop system. The field trial will employ a randomized complete block design with four replicates. Both field and lab-based measurements of agronomic and soil responses will be conducted. The findings will provide valuable insights for organic farmers, agricultural advisors, and policymakers to increase productivity in a sustainable way from organic grain farming in the southeast region.
The objectives for the study are as follows:
- To compare the effect of reduced tillage and no-tillage techniques on the soil properties, establishment, and productivity of wheat-soybean double-crop and weed control in organic systems. Acquiring this knowledge enables practitioners to minimize soil disturbance, maintain soil health, and mitigate ecological impacts within organic agricultural systems.
- To assess the gross productivity of the organic wheat soybean double-crop system compared to the full-season soybean system. This information aids farmers in making informed decisions regarding the adoption of specific cropping systems, considering factors such as productivity, resource efficiency, and environmental conditions.
- To evaluate the influence of environmental factors, such as radiation, temperature, and moisture availability, on the growth and yield of organic double-crop soybean following wheat harvest. This information facilitates the devising of adaptive strategies to optimize yields and enhance crop resilience under southeastern climatic conditions.
- To provide evidence-based recommendations for sustainable organic grain farming to producers and other stakeholders through well-developed extension and outreach activities. Disseminating this valuable information allows farmers to increase productivity, economic stability, and ecological sustainability in organic agricultural systems.
Research
The study was conducted within established organic grain rotation trials at the University of Tennessee’s Organic Crops Unit, East Tennessee Research and Education Center (ETREC), Knoxville, TN. These trials evaluate the effects of tillage intensity on agronomic, soil health, and economic outcomes during the transition to organic management. The one-year study was designed to address key knowledge gaps in organic wheat–soybean double-cropping systems and to identify management practices that enhance productivity, soil health, and profitability. The specific objectives were to (1) assess the effect of tillage intensity on crop performance and weed dynamics, (2) evaluate changes in soil organic carbon and inorganic nitrogen at different crop growth stages, (3) monitor environmental parameters such as soil moisture and temperature to interpret crop–climate interactions, and (4) analyze the overall system performance to guide recommendations for sustainable double-crop management in organic systems.
Treatments combined two tillage systems, intensive tillage (IT) and reduced tillage (RT), with two cropping systems, wheat–soybean double-crop (DC) and full-season soybean (FS). Based on previous research, a 3.6 maturity group (MG) soybean variety was selected for the FS system, and a 3.1 MG variety for the DC system. In the FS soybean system, the IT treatment involved initial tillage with an offset disk followed by planting a triticale–radish cover crop mix. After termination with a flail mower, residues were incorporated using a pick-up disk before planting soybeans. The RT treatment used the same cover crop mix, which was terminated with a roller-crimper, and soybeans were directly seeded into the residue without additional tillage. In the DC system, the IT treatment included winter wheat establishment after offset-disk tillage, with residues flail mowed and incorporated using pickup disk before planting DC soybeans. In contrast, the RT treatment involved minimal soil disturbance, where wheat residues were flail mowed and left on the surface as mulch prior to soybean planting. No manure or irrigation were applied to crops. Wheat received a split application of 4.9 Mg ha-1 of pelleted poultry litter. Weed management in no-till soybeans relied on OMRI-certified organic contact herbicides applied pre-plant and at the vegetative stage and on inter-row cultivations in the tilled plots.
Weed biomass, soybean yield, and soil samples were collected from 0-15 cm at three crop stages (planting, vegetative, and harvest) to evaluate changes in soil inorganic nitrogen (SIN) and soil organic carbon (SOC). Environmental data, including temperature, rainfall, biweekly soil moisture, and growing degree days (GDD), were recorded using an on-site weather station and soil moisture sensors. The collected data were statistically analyzed to assess the effects of tillage and cropping system on crop performance, soil properties, and environmental responses. Overall, the methodology combined field experimentation, laboratory analyses, and environmental monitoring to evaluate productivity, resource-use efficiency, and sustainability of organic wheat–soybean double-crop systems in the southeastern United States.
Crop performance and system productivity:
Wheat yield was not significantly affected by tillage management (p = 0.45), averaging 4.25 ± 0.59 Mg ha-1 in the IT treatment and 4.92 ± 0.50 Mg ha-1 in the RT treatment. Tillage intensity did not affect the yield, indicating reduced tillage is a viable option for wheat production. Among soybeans, FS soybeans showed no significant yield response to tillage (p = 0.44), averaging 0.65 ± 0.20 Mg ha-1 in IT treatment and 0.48 ± 0.04 Mg ha-1 in RT treatment. In contrast, DC soybeans exhibited a significant yield advantage under IT treatment (0.69 ± 0.11 Mg ha-1) compared with RT treatment (0.23 ± 0.10 Mg ha-1, p = 0.03). The higher double-crop yield in IT treatment is attributed to residue incorporation and improved seedbed conditions following wheat harvest, while the no-till mulch layer in RT treatment reduced nutrient availability and slowed early-season soybean establishment. These results suggest that, in organic grain production, moderate tillage may support better double-crop establishment and enhance productivity of both wheat and soybeans.
Environmental and soil health responses:
Seasonal soil moisture declined from 35% to 15% in FS soybeans and from 21% to 14% in DC soybeans, with no significant differences between treatments across the growing season. The 2024 growing season had no abnormal temperature or rainfall patterns (3215 and 2608 GDD; 505 and 396 mm rainfall for FS and DC soybeans, respectively). Soil organic carbon concentrations varied by depth and sampling stage but showed no treatment effect within each crop. When year-to-year changes in SOC were compared, FS soybeans lost soil C (−6.5 and −2.6 g kg-1 in IT and RT treatments, respectively) while DC soybeans gained C (+0.98 and +1.67 g kg-1 in IT and RT treatments, respectively). These changes could be attributed to crop rotation effects. The manure applied during the previous corn phase likely increased SOC prior to the full-season soybean rotation, and its gradual mineralization contributed to SOC decline following the soybean harvest. In contrast, in the double-crop soybean system, manure application to the preceding wheat and additional biomass inputs during the current year promoted an overall increase in SOC. Inorganic N levels were higher under IT treatment (8.1–8.6 mg kg-1) than RT treatment (4.3–6.1 mg kg-1), consistent with greater mineralization from incorporated residues and increased soil aeration. Although this enhanced mineralization supported short-term crop growth, it likely contributed to a faster turnover of organic matter, reinforcing the observed decline in SOC under the IT treatment.
Weed suppression and system interactions:
Weed biomass differed significantly among treatments in DC soybeans (p = 0.02), with greater weed pressure under RT treatment (2.57 ± 0.13 Mg ha-1) compared to IT treatment (1.99 ± 0.13 Mg ha-1). This difference was likely due to faster canopy closure and more effective early-season weed suppression in the IT treatment, whereas the RT treatment relied primarily on organic herbicide applications for weed control. Across both FS- and DC-soybean systems, a strong negative correlation was observed between yield and weed biomass (r = −0.95, p < 0.001), confirming weeds as a key yield-limiting factor in organic soybeans. In the combined model, crop type and tillage both significantly influenced weed biomass (p < 0.01 and p = 0.02, respectively), though their interaction was not significant. Increased weed prevalence in DC soybeans is likely due to late planting and reduced canopy competition. Therefore, the soil health benefits of no-till in these systems must be balanced against its increased risk of weed proliferation.
Comparison with conventional systems and project implications:
Compared with regional conventional DC systems, which typically yield 2.0–2.7 Mg ha-1, organic soybean yields were substantially lower due to the absence of synthetic fertilizers and herbicides. However, the organic IT system maintained productivity comparable to other transitional organic trials in the region, while RT treatments showed promising early signs of SOC retention. Using verified 2024 organic farm-gate prices ($13.35 bu-1 for wheat and $20.50 bu-1 for soybeans), the DC system produced gross returns of $2,604 ha-1 under IT and $2,587 ha-1 under RT, while the FS soybean system yielded $490 ha-1 and $362 ha-1 in IT and RT treatments, respectively. Although IT had higher soybean yields, RT achieved higher wheat yields, and the overall system revenues were nearly identical. These findings demonstrate that reduced tillage can achieve comparable gross returns to intensive tillage while delivering additional environmental benefits such as lower fuel use, improved soil structure, and enhanced carbon retention potential. In contrast, the single-crop soybean system generated substantially lower revenue per area, reinforcing the economic value of intensifying organic rotations through double cropping.
Overall, the project demonstrates that moderate tillage reduction is both agronomically feasible and economically competitive in Southeastern organic DC systems when combined with manure fertilization during the small-grain phase and targeted weed control in soybeans. The comparable profitability between IT and RT treatments paired with early indications of soil carbon gains in RT illustrates that organic producers can progressively transition toward reduced tillage without economic sacrifice. Continued multi-year monitoring will be essential to determine whether the observed SOC improvements under reduced tillage translate into lasting fertility benefits that offset initial yield variability, supporting the project’s long-term goal of developing profitable, ecologically balanced, and resilient organic DC systems for the Southeastern U.S.
Educational & Outreach Activities
Participation Summary:
Over the course of this project, multiple outreach and educational activities were conducted to engage farmers, students, and agricultural professionals in sustainable organic double-cropping practices. Two individual consultations were conducted with organic producers from Gibson Blueberry Farm and Sequatchie Cove Farm, along with extension agents, to discuss management challenges associated with reduced tillage, residue management, and double-crop establishment. Three educational resources including a factsheet on soil health indicators, a double-crop management infographic, and a field data summary sheet were created and distributed during outreach events. Three field tours were organized during the growing season for visiting farmers, students, and researchers to observe treatment effects on weed suppression, soil quality, and soybean performance. The project team also delivered three formal presentations, including two conference talks at 2024 Pick TN conference in Franklin, TN followed by 2024 ASA, CSA, SSSA annual conference in San Antonio, TX and a departmental seminar at the University of Tennessee, Knoxville. The project team also hosted an interactive field day and on-farm demonstration in at the Organic Crops Unit, Knoxville, TN with a focus on wheat–soybean double-cropping under contrasting tillage systems, highlighting the feasibility of organic no-till and residue-retention practices for weed management.
In total, approximately ten farmers and twenty agricultural professionals participated in these activities. The events fostered meaningful discussion around soil conservation, weed management, and double-cropping opportunities under Southeastern conditions. Outreach in progress includes an extension bulletin for organic producers summarizing early soil carbon and yield trends, and a short educational video for online dissemination. Collectively, these efforts strengthened the connection between research and practice, expanded awareness of reduced-tillage organic systems, and laid the groundwork for continued collaboration among growers, educators, and researchers working toward sustainable organic grain production in the region.
Project Outcomes
This project strengthened the foundation for sustainable organic grain production by demonstrating that double-cropping and reduced tillage can improve profitability, soil health, and system resilience for Southeastern farmers. The double-crop wheat–soybean system increased gross income nearly fivefold compared with single full-season soybeans, offering a clear economic incentive to intensify land use while maintaining soil-conserving practices. Our findings from the project indicated that reduced tillage can achieve comparable returns to intensive tillage with fewer field operations, lower fuel costs, and improved long-term soil structure. Environmentally, the reduced-tillage systems showed evidence of soil carbon gains in double-crop soybeans and overall stability of soil organic matter, indicating progress toward regenerative soil management under organic production. Weed suppression improved with moderate tillage and early-season control measures, enhances yield stability for the farmers without reliance on synthetic inputs. On-farm demonstrations and consultations helped farmers gain confidence in adopting double-cropping practices, improved their understanding of local organic grain market opportunities, and encouraged collaboration with researchers on management refinements. Overall, the project showed that reduced-tillage double-crop systems can simultaneously enhance farm profitability, soil health, and resource efficiency, providing a realistic and region-specific pathway toward long-term agricultural sustainability in the Southeastern U.S.
During the course of this project, our team’s understanding of sustainable agriculture deepened substantially, particularly regarding the management and optimization of organic DC systems in the warm and humid Southeastern conditions. We learned that reduced tillage is a viable and promising strategy for managing organic grain systems and can effectively replace intensive tillage without compromising productivity. Through field evaluations, we also recognized the potential of low-maturity soybean varieties to better fit the shorter growing season following cover crops or wheat harvest, enabling earlier harvest and timely establishment of winter cover crops before the onset of harsh conditions. Close monitoring of SOC dynamics revealed encouraging signs that even under intensive continuous cropping, there is scope to enhance SOC storage through reduced tillage practices. Early weed interventions (both pre-plant and during vegetative stages) proved effective, improving weed suppression in organic systems. Additionally, this project provided valuable insights into yield variability under different weather patterns, helping us better understand the influence of temperature and precipitation fluctuations on soybean productivity.
Our attitude and professional perspectives toward sustainable organic systems evolved through direct engagement with local producers and researchers. Conversations with farmers increased our awareness of the emerging local market potential for organic grains, while regional collaborations led to a new NIFA-funded project, “Tapping the Potential of Double Cropping for Profitable Organic Grain and Forage Production in the Southeast U.S.” This continuation will build on the lessons learned from this SARE study. In terms of skills development, Ph.D. students and undergraduate assistants gained hands-on experience in field design, soil and crop data collection, laboratory analyses, and statistical interpretation. Farm managers tested multiple residue and tillage strategies, contributing practical insights to research decisions. The project also enhanced communication and leadership skills as the principal investigator and team members shared findings with peers, extension professionals, and farmers across the region.
Finally, our awareness of regional opportunities for sustainable agriculture increased through collaboration and farmer dialogue. Tennessee’s legacy as a pioneer in no-till farming provided a unique context for exploring its organic adaptation, and we found farmers receptive and optimistic about transitioning to reduced-tillage organic systems. These collaborations are already resulting in successful on-farm adoption of double-cropping practices, informed by our project’s recommendations on variety selection, planting timing, and early weed management, collectively advancing the region’s capacity for resilient, soil-conserving organic grain production.
Future studies should focus on long-term monitoring of reduced-tillage and double-crop systems to validate the short-term gains in soil carbon, yield stability, and profitability observed in this project. Additional research is needed to identify and develop region-specific crop varieties that are better adapted to Southeastern climatic conditions and resistant to local pests and diseases, ensuring reliable performance under organic management. Expanding farmer–researcher partnerships will be critical to refine management practices, strengthen knowledge exchange, and promote adoption of sustainable double-cropping systems across diverse farm scales.
We sincerely appreciate the funding and support provided by Southern SARE, which enabled meaningful collaboration, farmer engagement, and the generation of applied knowledge to advance sustainable organic grain production in the Southeastern United States.