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.