Vegetable grafting was recently introduced in North America and has attracted interest from various stakeholders. The technology has been practiced for hundreds of years since it was first used for increasing the fruit size of gourds in China during the fifth century (Lee and Oda, 2003). It has been nearly 80 years since it was first introduced as a pest management practice for commercial watermelon (Citrullus lanatus) production (Tateishi, 1927). Today, grafting is applied to various vegetable species of both Cucurbitaceae and Solanaceae families. The total amounts of grafted plants used in commercial production fields and greenhouses are reportedly 766 million in Korea (estimated in Lee et al., 2010), 550 million in Japan (per survey results conducted by MAFF, 2011), and 130 million in Spain (F. Perez Alfocea, personal communication). These numbers are increasing every year as a result of limited options for addressing soilborne diseases and pests with increasing concern for the environment, sustainability, and food safety. In particular, the quickly approaching phase-out completion of methyl bromide in 2015 among developing countries (UNEP, 1997) is encouraging these countries to use more grafted plants as supplemental control measures to replace currently used methyl bromide applications in addition to the developed countries who were supposed to complete the phase-out by 2005.
In the United States, grafted tomato (Solanum lycopersicum) seedlings have been used by greenhouse hydroponic tomato growers as a result of increased yields throughout the long production cycle from a more vigorous rootstock (Kubota et al., 2008). These seedlings are typically grown in a so-called “high-tech” greenhouse, often with glass-glazing, advanced climate control system, subirrigation, CO2 enrichment, and supplemental lighting. Nearly all these grafted seedlings for greenhouse production are produced in Canada where more greenhouses and the supporting industries like grafting nurseries are clustered (in British Colombia and Ontario). These nurseries are crucial sources of grafted plants currently used in greenhouses. As an example, all large greenhouse tomato industries in Arizona, Texas, and California purchase millions of grafted plants shipped in from nurseries in British Columbia, Canada, every year. For example, a large commercial greenhouse located in Arizona imports nearly five million grafted tomato plants every year. Price for grafted tomato seedlings (excluding seed costs) in recent years have ranged from $0.40 to $0.90 per plant for young seedling plugs of two to three true leaf stage to $1.50 per mature flowering plant with two side shoots (or “double-headed plants”) grown in 4-inch rockwool cubes.
Compared with these Canadian nurseries supplying plants to greenhouses, the controlled-environment technology level of traditional American nurseries serving open-field producers is relatively low. Quonset-style single- or double-layered polyethylene-covered houses with roll-up side vents and overhead irrigation are the predominant structure type. Plants are typically grown in high density (≈1000 plants per m2) to reduce the cost per plant. The price range for non-grafted conventional seedlings for open-field fresh market tomato is as low as $0.02 to $0.03 per plant (not including seed costs). Clearly, the current technology and therefore the price used in transplant production for greenhouse and open-field fruiting vegetable production differ greatly. To make the grafting technology viable solution for open-field vegetable production, lowering the price of grafted plants seems to be an important key as demonstrated by Djidonou et al. (2013).
Although the efficacy of grafting has been reported by many research groups worldwide, the implementation (capital input) and operation (variable input) costs are relatively unknown. Among references available, Rivard et al. (2010) analyzed two cases of small nurseries located in the eastern United States who produced ≈1,000 to ≈10,000 grafted seedlings in 2008 and reported that production costs (labor and material costs) per grafted plant were $0.59 to $1.25, including seed costs. Barrett et al. (2012) estimated grafted seedling costs (labor and material costs) at $0.78 per plant (including seeds) for a target production level of 1000 plants. These reports on small grafted plant volumes are valuable because the growing industry segment among U.S. grafting users seems to be small farmers. However, the production scales examined were far below what would be relevant for applying this technology as a major pest management tactic for U.S. open-field vegetable production. When the industry attempts to initiate large-scale grafting operations in the United States, “underinvesting” may cause difficulty in maintaining consistent quality products. In addition, the potential for “overinvesting” in unneeded equipment may result in premature failure from lack of unmanageable debt.
Although economic analyses based on the real nursery situation (in situ analysis) are critical for the costs and benefit scenario specific to the cases, a limitation of in-situ analysis is that the outcomes are not scalable or applicable to different cases. Therefore, we developed a set of mathematical models that can be used to simulate the capital and variable costs over various cases considering different technologies and scales of nursery operation and perform sensitivity analyses of selected inputs and key parameters. These models are used also in a dynamic simulation considering potential randomness of events and actions in the operation (Meng et al., 2013). The intention of the present report is to provide the user with s reasonably accurate variable cost per plant and capital cost based on user input and selected scenarios applicable to most commercial nurseries in the United States.
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