Florida ranks fifth in the nation for vegetable production occurring on 265,835 acres with a market value of $2.65 billion in 2007 [U.S. Department of Agriculture (USDA), 2009]. Florida agriculture capitalizes on a market window for fruits and vegetables during the winter and spring months that other states cannot meet because of climatic limitations, thereby often receiving higher prices.
As demand for organic produce increases, growers are attracted to organic production since price premiums can offset the higher production costs. According to the 2008 Organic Production Survey from the USDA census of agriculture, 14,540 organic farmers and ranchers used 4.1 million acres of land in the United States with $3.16 billion in total crop and livestock sales (USDA, 2010). However, organic producers face challenges in meeting the National Organic Program (NOP) standards for organic certification.
According to the NOP, organic producers must use inputs for production that are from natural sources and will have minimal impacts on the environment (USDA, 2000). Nutrient management for organic production requires attention and careful application to provide sufficient quantities of nutrients that are available for use by the crop at the appropriate time. A survey found that the three most common sources of nutrients used by organic producers in Florida were 1) animal (especially chicken) manure, 2) bagged organic fertilizers, and 3) fish emulsion (Swisher and Monaghan, 1995). It was noted that the bagged fertilizers were also mostly based on poultry manure. Hildebrand et al. (1997) surveyed northern Florida organic growers and also found that chicken manure ranked first and fish emulsion as the second most commonly used source of fertilizer. The major constraints of using natural sources of fertilizers are the bulky nature and the heavy application rates needed to meet the nutrient requirements of the cash crop. The average nitrogen (N) content of chicken manure is 26–72 lb/ton of manure, and application rates are commonly 5–25 tons/acre per year (Ferguson and Ziegler, 2004). Utilization of an on-site source of N greatly reduces an organic grower's need for off-site nutrients. A solution for organic growers to reduce their fertilizer costs is to add a cover crop into their cropping system that increases the nutrient availability in their soils. Leguminous cover crops can provide biologically fixed N to the soil in addition to providing other benefits, such as soil stability, water retention, reduced erosion, and cycling of other nutrients.
An additional consideration for organic producers is weed management (Walz, 1999). Organic producers are limited to cultural practices, mulching with fully biodegradable mulches, mowing, livestock grazing, hand weeding, mechanical cultivation, flame or heat, and plastic or synthetic mulches, which must be removed at the end of the season (USDA, 2000). If these methods are not sufficient in managing weed populations, organic growers may use biological or botanical substances (USDA, 2000). However, a few nonsynthetic herbicides are currently available, and these substances for weed management are allowed only as a last resort option, and are often expensive.
Hildebrand et al. (1997) found that in north-central Florida weed management was the major constraint to switching from conventional to organic production. Weeds also limit the expansion of organic production. A strong reliance on hand hoeing and mechanical cultivation for weed management by Florida's organic vegetable growers was reported by Swisher and Monaghan (1995). Although the NOP allows application of permitted herbicides and other weed management techniques, organic producers continue to rely heavily on human labor and mechanical equipment to manage weed populations. The majority of organic producers in Florida manually cultivate as often as five to six times during a growing season to manage weeds (Swisher and Monaghan, 1995). With the cost of fuel and labor rising and possible adverse effects of frequent cultivation, organic weed management could benefit from a more ecological approach.
In Florida, organic producers generally do not grow crops during the hot, humid, summer months. This break in their crop production cycle is often left as a weedy or clean (usually with tillage) fallow. Although tillage suppresses weed populations to an extent, tillage can build the weed seed bank and spread weed seeds (Froud-Williams et al., 1983). Additionally, tillage is sometimes overused, and uses labor, machinery, and fuel that could otherwise be spared, and can contribute to soil erosion and loss of nutrients. Florida organic producers could use cover crops or green manures as tools for managing weed populations and as an alternative to a weedy fallow during the summer months. Despite the significant amount of literature and data to support the adoption of cover crops into cropping systems for environmental reasons, few economic studies of the use of cover crops have been conducted, and a gap exists in the understanding the economics of using cover crops (Lu et al., 2000). The costs associated with establishing a cover crop (seed and management) are easy to evaluate, but the benefits that do not have economic values are often excluded from the economic considerations of cover crop use. There is a need to appoint economic values to the benefits that cover crops provide to a cropping system.
Cash crops following cover crops often experience reductions in weed populations as compared with cash crops following a weedy fallow. These reductions can lead to benefits including an increase in cash crop productivity and potential reductions in pest pressure (Li et al., 2006). In organic systems, this reduction in weed populations could mean a decrease in labor costs associated with hand weeding. Although the importance of weed suppression by cover crops is well documented, economic data are lacking to support the monetary benefits growers might obtain by using a cover crop in place of a weedy fallow (Snapp et al., 2005). Sangakkara et al. (2006) evaluated crops that could be used in place of weedy fallows in tropical farming systems. Weed suppression by a cover crop correlates to the biomass production of that crop (Klassen et al., 2006). Sunn hemp produced the most groundcover and, therefore, the greatest weed suppression in comparison with other cover crops, suppressing 50% to 82% of weeds (Sangakkara et al., 2006). The study also showed that a cash crop of mung bean (Vigna radiata) following the sunn hemp fallow had the lowest weed populations.
Many growers recognize the benefits of integrating a cover crop into their cropping systems; however, it is difficult to justify the costs to implement these cover crops. The objective of this study was to conduct economic analyses of summer fallow treatments in Florida. The economic analyses were focused on the evaluation of the costs for cover crop establishment and management and on the appointment of economic values to cover crops, emphasizing the nutrient accumulation and the weed suppressive capabilities and how these benefits interact with the overall cash flow of the cropping system.
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