This two year project involved farmer collaborators with row crop, vegetable and citrus operations and was designed to identify best practices for cover crop integration in their respective systems. Objectives for cover crop services included: nitrogen contribution (row crop), nematode suppression (vegetable) and weed suppression (citrus). A variety of cover crop species and methods of planting and termination were examined at each location.
Florida’s 47,000 farms produce more winter vegetables and citrus than any other state. Approximately 15% of farmers contribute to 90% of the acreage and gross annual sales of fruit, vegetable and row crops. In the past decade, a significant investment has been made by the Florida Department of Agriculture and Consumer Services (FDACS), the Department of Environmental Protection’s Water Management Districts and the University of Florida (UF) to develop Best Management Practices (BMP) management programs that will reduce the amount of nitrogen (N) and phosphorus (P) entering surface and ground water (FDACS, 2006). The BMP manuals outline practices in checklist format that are aimed to reduce nutrient loading from non point source pollution attributed to agriculture. Approximately 60% of farmers have signed an agreement with FDACS pledging to follow BMP practice standards. Signing is voluntary but may become mandatory if the state’s water quality does not improve. In order to remain compliant, the farmers must limit fertilizer N and P to the rates recommended by UF (Olson and Simonne, 2009). The BMP manuals recommend cover crops to reduce soil erosion however; the risk of erosion is minimal in most of Florida, with exceptions in the panhandle and hilly areas surrounding the citrus ridge (NRCS, 2009). The manual does not recognize legume N contribution or other ecosystem services such as pest suppression and soil carbon sequestration to the overall management plan. Farmers complying with BMP programs with cover crops do not currently reduce N applications following legume cover crops despite significant biomass production and N accumulation from common species (120-319 kg ha-1 N) (Cherr et al., 2006, Wang et al., 2009). The University of Florida recommends that 50% of the total N from plant- and animal-based amendments be assumed available during the course of the production season. In reality, this one-size-fits-all approach does not contribute to smart N management. The risk of N leaching from the deep sandy soils of FL combined with the lack of an accurate model to predict N release from organic amendments often results in inadequate or excessive N thus either reducing yield or contributing to a decline in water quality. Growers who lack quantitative data on their own farms are often hesitant to utilize cover crops for nematode and weed suppression. Nematode management in conventional systems includes fumigation and current chemistries are only partially effective. A significant effort has been made by Florida nematologists to identify cover crop species that suppress nematode populations in farming systems. There is strong evidence that the influence of species on nematode populations varies by cover crop cultivars (Kruger and McSorley, 2008; Wang et al, 2006). Seed is often bulked from several source locations, and attribution to cultivars is difficult. Cover crops can offset costs of weed management by suppressing weed seed germination and establishment (Collins et al., 2007; Linares et al., 2008). We estimate less than 40% of producers use cover crops, but their primary reason is to capture residual N and not to suppress pests.
- In the row crop system, determine if a legume cover crop can partially offset crop nitrogen requirements in a cost efficient manner.
- In the vegetable system, identify an alternative cover crop to sorghum sudangrass that can contribute a similar amount of biomass to the soil at termination and that can contribute to nematode suppression.
- In the citrus system, determine the best management strategy for integrating cover crops in citrus alleyways and select a species that can contribute to weed suppression and nitrogen contribution.
Program activities occurred at three locations including two farms and the UF-IFAS Research and Demonstration Unit in Hastings, FL. Farmers in the Hastings area decided collectively that the research station would be the best location for the project since it would be available for all of them to visit as they wished and that they would be able to compare this trail to other concurrent trails on potato for a more holistic discussion and learning experience. Our original plan was to conduct the studies at each location for two years, however, due to the desire by the team to address our objectives as thoroughly as possible, we decided to expand the study at the Hastings location to include the potato production. The original proposal called for data collection on cover crops and nematodes only, but by including the potato yields and subsequent soil sampling, we were able to capture some effects of our treatments on the subsequent crop. Because of the additional costs and time incurred as a result of the extended season, we conducted the study for only one year at the Hastings location. Row crop system – Nitrogen Contribution Treatments were established on two different locations in 2010-2011 and 2011-2012. Each site was larger than 20 acres, and treatments were arranged in a randomized complete block design and replicated four times. Winter cover crops were planted to follow peanut each year, and preceded corn. In 2010, treatments included: cereal rye (Secale cereale L. ‘FL 401’) with either 0, 30 or 60 lbs/a nitrogen (N) applied four weeks after planting as ammonium nitrate, rye plus lupine () and 30 lbs/a N and rye plus crimson clover () and 30 lbs/a N. Because…..In 2011, Vegetable system – Nematode Suppression Four cover crop treatments were randomized in a complete block design and replicated four times following potato harvest. Treatments were as follows: sorghum sudangrass, pearl millet ‘Tiffleaf 3’ plus lab lab (Lab Lab purpurea ‘Rongai’), Sorghum sudangrass incorporated, overseeded with tillage radish () at 20 lbs/a, and sunn hemp at 25 lbs/a, incorporated and overseeded with tillage radish at 20 lbs/a. Cover crop seeds were planted on July 15, 2010 and terminated on October 28. On October 28, tillage radish was seeded in the sorghum and sunn hemp treatments. Citrus system – Weed Suppression Treatments were established in 2011 and 2012 on certified organic land, and all inputs and management plans were consistent with the farmer’s Organic Farming plan. In November 2011, four treatments were arranged in a strip block design and replicated four times: sunn hemp (Crotalaria juncea L.) seeded to 30 lbs/a, lupine seeded to 50 lbs/a, lupine seeded to 100 lbs/a, and a weedy fallow. Legumes were inoculated with approved inoculant and seeded with a no-till drill in native vegetation that was almost exclusively Guinea grass (Panicum maximum), a common non-native tropical grass considered a weed in agricultural systems.
Row Crop System – Nitrogen Contribution Vegetable System – Nematode Suppression Stunt and stubby nematodes were present throughout the season, with peak numbers in the fall. During cover crop production, sorghum sudangrass alone had more stunt and stubby nematodes than sorghum followed by tillage radish or sunn hemp. In March 2011, stunt nematodes were as follows: SS> SS+R=PM+LL>SH. There were no differences among treatments for stubby nematodes, and densities of ring and spiral nematodes were minimal and their numbers were too low for accurate statistical analysis. Citrus System – Weed Suppression Weed suppression was the primary objective at this location, but nitrogen contribution was also a consideration. The timing of N availability is primarily important during the spring growth flush that occurs in February in central FL, prior to floral initiation in March. There is some nitrogen demand in the fall as well as fruit matures, but it is not as punctuated as the spring demand. Therefore, we selected a legume with rapid establishment to outcompete weeds, minimal management demands to keep costs low, and the potential for N contribution. Optimally, the crop needed to be terminated 6-10 weeks after seeding, depending on weather and crop conditions.
Educational & Outreach Activities
Conference Posters and Presentations D. Treadwell, B. McLean, K. Brock, and G. England. Alternative Soil Management. Small Farms and Alternative Enterprises Conference Organic and Sustainable Farming Track, July 2011.This session was designed for experienced farmers interested in improving the technical skills required to achieve specific objectives in their farming systems through cover crop integration and other strategies. McLean and Brock presented an overview of their systems and discussed the lessons learned during the project. A discussion followed, with most participants inquiring about equipment issues, approach to select species, and metrics to evaluate success. D. Treadwell. Cover Crops for Vegetable Production in the Gulf States. Mississippi Fruit and Vegetable Grower’s Association Annual Meeting. (Invited) Vicksburg, MI October 2011. Preliminary data, images, and grower perspectives from this project were central to this presentation to Mississippi farmers, Extension faculty, and industry leaders (attendance 120) D. Treadwell. TriCounty Area Extension and Research Planning Meeting, November 2011. Presented and lead discussion among county administrators, extension faculty, growers, and station staff on this project’s progress and recommended next steps. Factsheet/Media The following University of Florida fact sheets were revised in 2012 to reflect new information as a result of this project: Treadwell, D.D., W. Klassen and M. Alligood. 2008. Annual Cover Crops in Florida Vegetable Systems. Part I. Objectives: Why Grow Cover Crops? EDIS. http://edis.ifas.ufl.edu/HS387 (Minor revision in 2012) (12,244 Downloads 2008-2012) Treadwell, D.D. W. Klassen and M. Alligood. 2008. Annual Cover Crops in Florida Vegetable Systems. Part II. Production. http://edis.ifas.ufl.edu/HS389 (with video clip) (Minor revision in 2012) Treadwell, D.D. W. Klassen, M. Alligood and S. Shewey**. 2008. Annual Cover Crops in Florida Vegetable Systems. Part III. Buying and Sourcing. http://edis.ifas.ufl.edu/HS390 (Minor revision in 2012) (15,598 Downloads 2008-2012) Integrating Cover Crops in Vegetable Systems. Farmer Field Day Cover Crops in Vegetable Systems Field Day, Hastings, FL, Oct 26, 2010. Six farmers representing approximately 80% of the potato acreage in the TriCounty Area (St. John’s, Putnam and Flagler Counties) toured the experimental area and examined the treatment responses. Key objectives (nematode suppression and ability to integrate cover crops with the equipment and timing of field activities typical of potato growers) and the team’s approaches to achieve those objectives were discussed. In-service Trainings D. Treadwell led a session Small Scale Cover Crop Integration for 93 county faculty and master gardener coordinators and volunteers in Hastings, FL on October 15, 2010. Following a formal presentation in the classroom, attendees were introduced to this project in the field and examined the treatments during a 30 minute discussion period. D. Treadwell and M. Alligood lead the session Active Vegetation Management: Cover Crops at the IMP for Specialty Crops In-Service Training, Live Oak, FL May 14-15, 2011. Twenty five county Extension faculty and agency technical service providers participated in this two-day training that combined formal classroom instruction with hands-on learning. Activities included scouting methods, diagnostics with living insect and disease samples using microscopes, and small group work in the field to diagnose common and uncommon pest management problems. Cover crop species used in this project were planted in advance of this training to provide participants with a living laboratory to test their knowledge and skills.
All farmer collaborators increased adoption of cover crops, and in addition, many additional farmers introduced cover crops into their system for the first time, experimented with a different cover crop species, or increased the acreage they had in cover crops. The row crop farmer-collaborator continues to expand his approach of conservation tillage in his operation and is now focusing his efforts on cover crop mixtures rather than monocultures as a result of this project. He is a vocal advocate for cover crops and their contributions to the farming system, and interacts with many researchers and agency personnel. During the period of this project, we benefitted from open communication with several other research groups, including a group interested in how farming practices such as high residue cover crops can reduce irrigation demands (Love et al., 2012; Bartels and Brock, 2012). The citrus farmer-collaborator purchased new equipment, including a tractor and a custom-built roller-crimper to continue their efforts to increase the acreage of citrus alleys planted in cover crops. Cover crop seed is no-till drilled in alley ways on approximately 30 acres, and currently and they are focusing on sunn hemp as their primary summer cover crop species. In the TriCounty potato region, farmers continue to plant sorghum sudangrass in the summer preceding fall potato seeding, but they have changed the cultivar they use to one that is less attractive to nematodes. For potato farmers expanding to other specialty crops, several farmers are exploring different species including sunn hemp and millet. Due to the extension activities of this project, we captured the attention of other farmers in the state who decided to expand their cover crop activities. A row crop farmer with 6,500 acres in production planted a test plot of 150 acres of sunn hemp July 20, 2011 at rates of 30 and 15 lbs/a. Samples were collected on October 14, and the estimated dry weight of sunn hemp at the 30 lbs/a rate was 6,500 lbs/a. He is now in his third year of planting sunn hemp on his farm.
Areas needing additional study
Future studies should be directed at improving accuracy in the ability to estimate nitrogen availability from legume cover crops in subtropical conditions, fine-tuning the calendar recommendations for sampling nematodes relative to the height of the water table, identifying strategies to improve the treatment and handling of cover crop seed when harvested and stored on farm by the farmer, and continue to explore new cover crop germplasm to meet the diversity of farmer needs.