Optimizing cover crop interseeding time in organic corn to reduce resource inputs, build soil health, and boost profitability

Commodities

Practices

Sometimes looking to the past offers solutions for the future. An ancient cropping practice called "intercropping," or companion cropping, created a mutually beneficial ecosystem and a functional plant community to increase individual plant production. This approach entailed a multi-layered agro-ecosystem where different crops filled different functional niches. Two major benefits of this technique are lower input costs and improved crop protection from pests and diseases. While Native Americans used "three sister crops," including squash, corn, and beans for companion cropping, the underlying principles can be applied to improve the long-term productivity of larger and commercial farming operations. We propose cover crop interseeding into corn (one of the most resource-intensive crops) to enhance utilization of unused functional niches in corn production systems, improve soil-plant interactions, reduce resource inputs, and improve cropping system productivity. The project is built upon the lessons learned from the last six years of our research on cover crop interseeding with SARE support that started with an on-farm grant and followed with an R&E grant. The past studies identified cover crop species and seeding rates for interseeding under conventional and reduced tillage systems. The farmer surveys across the southeast identified that the success of interseeding in organic corn production systems is largely determined by interseeding at the right time. Thus, three planting systems (before, at, and after corn planting) were identified based on feedback from the farmer cooperators and stakeholders, which will be tested in the proposed project. The performance of the system will be assessed by agronomic and soil-health parameters, pest-control ability, and profitability. Our social science collaborator will engage growers to assess potential risks/benefits of each tested approach. Our economist will conduct a cost-benefit analysis based on monetary benefits, management costs, and potential disadvantages of each interseeding system. In the first two years, we will conduct field trials at Clemson University Organic Farm to identify the optimal interseeding time, which will be confirmed in farmer cooperators' commercial farms in the third year. One of the farmer cooperators will interseed cover crops in a 'corn maze' on his working family farm, establishing a unique education component for disseminating regenerative agriculture principles to elementary school children and the general public. Results will be disseminated to producers and agriculture professionals through field days, presentations at regional conferences and producer meetings, and print/online media. The project collaborators, including extension agents, NRCS and 1890 university personnel, and point-persons for small farmers will ensure effective outreach to various communities and farmer engagement throughout the project. By optimizing management and removing technical barriers to the adoption of cover cropping, farmers will benefit from building healthier soils, reducing the need for weed management, fertility inputs, and stabilizing economic viability. Reducing resource inputs will help protect natural resources; increasing crop and microbial components in the system will promote weather-related risk management strategies and resilient agriculture; and including family-farmers as cooperators will help strengthen the family farm system of agriculture- ultimately improving the community's quality of life.

1. Identify the optimal time for interseeding cover crops into organic corn in SC. Three systems will be evaluated: interseeding before, at, and after corn planting, based on their ability to suppress weeds and enhance microbial communities, nutrient availability, soil function, and corn yield under conventional and reduced tillage.
2. Quantify natural pest control benefits conferred by interseeded cover crops aboveground and belowground.
3. Evaluate economic consequences of interseeding based on monetary benefits, management costs, and potential disadvantages.
4. Engage growers to identify trusted and effective communication strategies that support informed adoption decisions for cover crop interseeding and improve perceived quality-of-life benefits for farmers.
5. Develop a collaborative outreach program to catalyze the integration of a regionally-specific interseeding system.

To test objectives 1-3, we will conduct field trials and evaluate four interseeding timings:

(i) Before corn planting - white clover living mulch planted in the Fall, and strip-tilled in the following Spring to plant corn

(ii) At corn planting - buckwheat drilled into corn inter-rows

(iii) After corn planting - buckwheat interseeded at corn's two-leaf (V2) stage

(iv) After corn planting - buckwheat interseeded at corn's four-leaf (V4) stage

The above treatments ii-iv will be tested under conventional and reduced tillage.

Rationale for selection of cover crop species

In this study, we will test white clover and buckwheat as interseeded cover crops.

Legume-based cover crops, when interseeded into organic systems, can lead to economic and environmental efficiency because of nutrient supply and control of soil erosion and nutrient leaching (Sanders et al., 2017). White clover can be a good option because it can be as effective as herbicides to control weeds (Hartwig and Ammon, 2002) and demonstrates shade tolerance (NRCS, 2011). White clover also encourages the association between mycorrhizal fungi and corn plants to assist in nutrient supply from soils with high phosphorous fixation capabilities (Deguchi et al., 2007). Importantly, Fall-planted white clover has been shown to be a suitable living mulch to which corn can be planted in the following spring, in our nearby states such as Georgia (Sanders et al., 2027) and Tennessee (Quinby et al., 2023). Further, white clover has been a reliable Fall-Winter cover crop in the field that we have selected for our on-station trial (personal communication with the farm manager).

Buckwheat was chosen as an interseeded cover crop for the proposed study based on our previous studies supported by the SARE (St Aime et al., 2023; also explained under Preliminary Research in the "Problem, Rationale and Significance" section). In our previous field trials in South Carolina, buckwheat appeared to be a suitable cover crop for interseeding with corn based on corn grain yield, corn biomass, weed suppression, and soil health improvements (Figures 2-7). Farmers have also shared success stories of the corn-buckwheat interseeded system (Loran Steinlage- row crop farmer, Presentation at the Conference on Building Soil Health: Principles, Practices and Profitability, Clemson, SC, 10/28/2019). Buckwheat's benefits include rapid establishment and land cover, strong weed suppression, phosphorous scavenging, and ability to thrive in low-fertility soils and attract beneficial insects (Clark, 2012). It produces abundant fine roots, which make the soil friable (Clark, 2012), thereby making this species a good choice for compacted soils in the Southeast.