Field production of fresh-market tomato.

Field experiments were carried out during Spring 2010 and 2011 growing seasons at the Suwannee Valley Agricultural Extension Center in Live Oak, FL (lat. 30.31°N, long. 82.90°W) on a Blanton–Foxworth–Alpin Complex sandy soil. The field-grown determinate tomato cultivar Florida 47 (Seminis Vegetable Seeds, St. Louis, MO) was used as scion and was grafted onto two commercially available interspecific tomato hybrid rootstocks ‘Beaufort’ (FL/BE) and ‘Multifort’ (FL/MU) (De Ruiter Seeds, Bergschenhoek, The Netherlands). The nongrafted ‘Florida 47’ (FL) was used as a control, representing current commercial production practices. The two rootstocks used in this study are among the most widely used tomato rootstocks in the United States at present. Scion seeds were planted on 23 Feb. 2010 and 21 Feb. 2011, 2 d after sowing the rootstock seeds. Tomato plants were grafted on 16 Mar. 2010 and 20 Mar. 2011 (Djidonou et al., 2013). In both years, 5 weeks before transplanting, field plots were disked and plowed, followed by soil fumigation using 1,3-dichloropropene + chloropicrin (Telone C-35; Dow AgroSciences, Indianapolis, IN) at the rate of 21.0 gal/acre a.i. Grafted and nongrafted plants were transplanted in raised beds with plastic mulch and drip irrigation on 29 Mar. 2010 and 1 Apr. 2011. Beds were 28 inches wide and spaced 5 ft apart with 18-inch in-row spacing for open-field tomato production, resulting in 5808 plants per acre. In both seasons, a randomized complete block design with four replications (blocks) was used. Plants were grown following the current University of Florida/Institute of Food and Agricultural Sciences recommendation for irrigation and fertilization program for commercial tomato production (Olson et al., 2009). The total fertilizer application rates were 200 lb/acre nitrogen, 6.5 lb/acre phosphorus, and 183 lb/acre potassium (Djidonou et al., 2013). Plants were trained using the standard stake and weave system. Tomato fruit that reached mature green or more advanced ripening stages were harvested at 80 and 88 d after transplanting (DAT) in 2010 and at 75, 85, and 92 DAT in 2011. Fruit were graded as extra large, large, medium, and culls (small fruit and defected fruit), and the tomato fruit in each grade were counted and weighed. Marketable fruit yield was then calculated as the total weight of extra-large, large, and medium fruit and was expressed as number of 25-lb cartons per acre.

Costs of grafted and nongrafted transplant production.

In this study, the costs of grafted and nongrafted transplants were estimated following the procedure described by Barrett et al. (2012b). All the materials, supplies, and labor associated with the production of grafted and nongrafted transplants were estimated to calculate the costs of nongrafted ‘Florida 47’ plants and grafted ‘Florida 47’ plants with ‘Beaufort’ or ‘Multifort’ rootstock.

Base production cost model for open-field production of fresh-market tomato.

For the purpose of this study, a base cost model for growing, harvesting, and marketing ‘Florida 47’ in a 1-acre field with a raised-bed polyethylene mulch production system was established using an existing crop budget model for fresh tomato production in the Manatee/Ruskin, FL area developed by the University of Florida Center for Agribusiness (2009). Costs of production inputs, including transplants and fertilizers during the 2010 and 2011 trials, were estimated and used in developing the actual production budget in this study. The variable costs of irrigation were estimated based on information provided by Pitts et al. (2002). A harvest and marketing charge of $3.39 per 25-lb carton (derived from the existing crop budget model described above) was used to estimate the harvest and marketing costs for total marketable tomato yields in 2010 and 2011, which included costs of containers, harvesting and hauling, packing, selling, and organization fees. The tomato shipping point prices of $10.95 (2010) and $11.95 (2011) per 25-lb carton during the harvest periods [U.S. Department of Agriculture (USDA), 2011)] were used in calculating the gross returns (crop value) of grafted and nongrafted tomato production.

Partial budget analysis of grafted and nongrafted tomato production.

Partial budget analysis is a standard economic analysis tool commonly used to determine the effects of a series of changes to certain operations of the farming production system on the change of returns (Sydorovych et al., 2008). This economic analysis approach compares the negative and positive effects of applying a new treatment relative to a base or standard treatment. It can provide a brief overview on the possible economic advantage that may accrue to growers adopting the new production practice. In the context of this study, using grafted tomato transplants is considered as the new treatment, whereas using nongrafted transplants is the standard practice. The typical components of partial budget analysis as presented by Sydorovych et al. (2008) were adapted as follows: 1) negative effects: added costs due to grafting, reduced returns due to grafting, and total negative effects due to grafting (i.e., the summation of added costs and reduced returns); 2) positive effects: reduced costs due to grafting, added returns due to grafting, and total positive effects due to grafting (i.e., the summation of reduced costs and added returns); and 3) total effect (i.e., net change in revenue): difference between total positive effects and total negative effects.

It was assumed that added costs of grafted tomato production relative to the nongrafted tomato production would be incurred if the costs of grafted transplants and the harvest costs of grafted plants were higher than the transplant and harvest costs of nongrafted tomato production. Furthermore, added returns would be incurred if the use of grafted plants resulted in higher yields, larger fruit size, and improved fruit quality, which means higher gross returns in grafted tomato production than in nongrafted tomato production.

Sensitivity analysis.

Fresh-market tomato prices fluctuate constantly within and across seasons. The sensitivity analysis was conducted to evaluate the effects of changes in the fresh-market tomato prices and grafted transplant costs on the net returns of grafted tomato production for each of the two production seasons. The analysis was performed for each grafting type using different combinations of scenarios involving variations in tomato prices (i.e., $8.95, $10.95, $11.95, $13.95, and $14.65 per 25-lb carton) and grafted transplant costs ($0.84, $0.67, $0.54, $0.43, and $0.34 per plant). The tomato prices were selected from the reported shipping point prices of mature green tomatoes per 25-lb carton in the past 7 years (USDA, 2011). Because lower tomato prices may lead to a more significant reduction in net returns of grafted tomatoes than nongrafted tomatoes, and the focus of the present study was to determine the economic feasibility of grafted tomatoes, only one lower price ($8.95) and two higher prices ($13.95 and $14.65) than the 2010 ($10.95) and 2011 ($11.95) base prices were used. In addition, because lower costs of grafted transplants will conceivably make grafted tomato production more economically feasible, one higher cost and three lower costs of grafted transplants than the base cost ($0.67) of grafted transplants were included. The cost levels of grafted transplants were determined by decreasing the highest cost ($0.84) by 20% gradually. At different tomato prices, the break-even analysis was also conducted to estimate the grafted transplant cost at which grafted and nongrafted tomato production would result in the same net returns when the nongrafted transplant cost was assumed to be fixed at the base level of $0.15/plant.

Costs of tomato transplant production.

Grafting involves the combination of two plants with distinctive traits to form a new plant. Hence, the use of grafted tomato transplants will result in additional costs inherent to materials, space, and labor needed for grafting. In this study, the cost associated with the production of ‘Florida 47’ grafted onto either ‘Beaufort’ or ‘Multifort’ was estimated at $0.67/plant vs. $0.15/plant for the nongrafted transplants (Table 1). On a per plant basis, our estimations showed that the grafted tomato transplant was 347% more expensive than the nongrafted plant. Such a price difference was consistent with that reported by Barrett et al. (2012b) on grafted organic heirloom tomato transplants using the ‘Multifort’ rootstock. Similarly, estimated costs were $0.59 and $0.13 per plant for grafted and nongrafted tomato transplants, respectively, in a commercial farming operation in North Carolina (Rivard et al., 2010b). In contrast, Besri (2003) reported only a 1-fold increase of tomato transplant price with grafting in Morocco (i.e., $0.19 and $0.38 per plant for nongrafted and grafted tomato transplants, respectively). Costs of grafted vegetable transplants also vary with the crop type. According to Taylor et al. (2008), the price of grafted seedless watermelon transplants was $0.87/plant as compared with $0.28/plant for nongrafted transplants. As indicated in the previous studies, the higher cost of rootstock seeds, rather than the labor costs of grafting operation, is often the main contributing factor to the increased costs of grafted plants. In the present study, the material cost accounted for ≈73% of the total costs of grafted transplant production. With the development of more rootstock breeding programs in the United States, it is anticipated that the rootstock seed price may decrease, thus reducing the cost of grafted transplants. Advancement in grafting techniques, including automation of the grafting operation, may also help lower the cost of grafted transplant production (Lee et al., 2010).

Table 1.

Estimated costs of nongrafted ‘Florida 47’ tomato transplants and ‘Florida 47’ transplants grafted onto ‘Beaufort’ or ‘Multifort’.

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With the planting density of 5808 tomato plants per acre used in this study, grafting with either ‘Beaufort’ or ‘Multifort’ rootstocks added about $3020.16 per acre to the total preharvest production costs in field production of ‘Florida 47’ (Table 1). This was in line with the report of grafted transplant costs in North Carolina, which indicated that the use of grafted tomato transplants would increase the production costs by $2275 per acre (O’Connell et al., 2009).

Costs of field production of fresh-market tomato.

In this study, the total costs per acre required to produce, harvest, and market ‘Florida 47’ tomatoes in the area of Live Oak, FL, using the raised-bed polyethylene mulch system with drip irrigation were estimated at $14,720.77 and $14,954.68 in Spring 2010 and 2011 production seasons, respectively (Table 2). Our estimated total production costs were slightly lower than the budget of $15,451.77 per acre developed by the University of Florida Center for Agribusiness (2009). Such differences were expected as our production budget accounted for the estimated costs of transplants, irrigation, and nutrient management during the field trials. In addition, the harvest costs estimated in our study reflected the marketable yields of nongrafted tomatoes measured in the 2010 and 2011 field trials. The total estimated costs of field tomato production in the present study were also comparable to the estimated cost of $16,926 per acre for producing and harvesting tomatoes in fumigated soils in North Carolina (Sydorovych et al., 2008).

Table 2.

Estimated costs per acre needed to produce, harvest, and market ‘Florida 47’ tomatoes in field production with raised-bed polyethylene mulch system in Spring 2010 and 2011 growing seasons in Live Oak, FL.

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These total estimated costs involved the variable and fixed costs associated with the preharvest operations and the costs needed for harvest and marketing. Specifically, the preharvest operational costs included the costs associated with transplants, irrigation, fertilization, and other management practices, which made up ≈66% of the total production costs. The harvest and postharvest operations, including packaging and marketing tomatoes, amounted to $4939.23 per acre and $5173.14 per acre in 2010 and 2011, respectively (Table 2).

Marketable fruit yield and gross returns.

In this study, yield increases as a result of grafting with interspecific rootstocks were demonstrated in both the 2010 and 2011 field trials. In 2010, the average marketable yields were 2024 and 1890 25-lb cartons per acre with ‘Florida 47’ grafted onto ‘Beaufort’ (FL/BE) and ‘Multifort’ (FL/MU), respectively, as opposed to 1457 cartons per acre for the nongrafted plants (Table 3). In 2011, these values were 2166, 2138, and 1526 cartons per acre for FL/BE, FL/MU, and FL, respectively. As a result, projected total harvest costs were higher with the grafted treatments as compared with the nongrafted ‘Florida 47’ during the two production seasons. For example, in 2010, the harvest cost of nongrafted ‘Florida 47’ was $4939.23, whereas the estimated harvest cost was $6861.36 in grafted tomato production with ‘Beaufort’ (Table 3).

Table 3.

Average marketable tomato fruit yields, harvest costs, and gross returns for nongrafted and grafted ‘Florida 47’ in field production with raised-bed polyethylene mulch system during Spring 2010 and 2011 in Live Oak, FL.

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The tomato selling (shipping point) prices of $10.95 (2010) and $11.95 (2011) per 25-lb carton during the harvest periods (USDA, 2011) were used in calculating the gross returns (crop value) of grafted and nongrafted tomato production. In 2010, the gross returns reached $22,162.80 and $20,695.50 per acre for production of grafted ‘Florida 47’ with ‘Beaufort’ and ‘Multifort’, respectively (Table 3). In contrast, the nongrafted tomato production was valued at $15,954.15 per acre. Hence, the additional gross returns relative to nongrafting were $6208.65 and $4741.35 per acre for ‘Beaufort’ and ‘Multifort’, respectively. In 2011, these additional gross returns were $7648.00 and $7313.40 per acre for ‘Beaufort’ and ‘Multifort’, respectively (Table 3). The gross returns were slightly higher in 2011 than in 2010 because of higher marketable fruit yields achieved in the 2011 season. A previous study of ‘Florida 47’ production in Live Oak, FL, showed the gross returns of $19,972 and $10,736 per acre in Spring 2005 and 2006 growing seasons, respectively (Gazula, 2009). These results indicated that the gross returns of field tomato production could vary considerably depending on seasonal changes of fruit yields and market tomato prices.

Partial budget analyses of grafted tomato production.

Typically, partial budget analysis describes the negative and positive effects associated with the use of alternative inputs or production practices. In terms of the production costs, the negative effects (added costs) related to the use of grafted transplants involved the increased costs of transplants and the harvest. These total negative effects amounted to $4942.29 and $4488.03 per acre with grafting ‘Florida 47’ onto ‘Beaufort’ and ‘Multifort’, respectively, in 2010; and $5189.76 and $5094.84 per acre in 2011 (Table 4). On the other hand, the positive effects associated with grafted transplants involved the added returns on the tomato fruit values, which ranged from $4741.35 to $7648.00 per acre over the two production seasons (Table 4).

Table 4.

Added costs and reduced returns, total negative effects, reduced costs and added returns, and total positive effects incurred by grafting ‘Florida 47’ tomato onto ‘Beaufort’ and ‘Multifort’ rootstocks in field production with raised-bed polyethylene mulch system during Spring 2010 and 2011 growing seasons in Live Oak, FL.

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The net return can be estimated as the difference between the gross returns and production costs. The transplant and harvest costs changed as a result of using grafted transplants, whereas other production costs remained constant regardless of the use of grafted transplants. The net return for each grafted treatment relative to the nongrafted treatment can also be calculated as the difference between the total positive effects of grafting and the total negative effects of grafting. After accounting for grafting and harvest costs, the net returns of grafting relative to nongrafting were $1266.36 and $253.32 per acre for grafted tomato production with ‘Beaufort’ and ‘Multifort’, respectively, in the 2010 season (Table 5). These relative net returns were $2458.24 and $2218.56 per acre in 2011. These values indicated that the increased crop value attributed to the significant improvement of marketable tomato fruit yield could offset the increased cost of grafted tomato production and even made it more profitable than nongrafted tomato production in fumigated soils. In this study, using the rootstock ‘Beaufort’ appeared to be more cost effective compared with ‘Multifort’, especially in the 2010 season, because of the higher marketable yield of grafted plants with ‘Beaufort’. However, the difference in net returns between grafted and nongrafted tomato production, as observed in the present study, was lower than that reported by O’Connell et al. (2009) in an organic, open-field production of determinate tomato in North Carolina. These authors found that the net return of the top yielding scion–rootstock combination, that is, ‘Celebrity’ grafted onto ‘RST-04-105-T’, was $59,635 per acre as compared with $8780 per acre for nongrafted ‘Celebrity’ tomato. It should be noted that such a great difference in net returns was owing to the high pressure of southern blight (caused by Sclerotium rolfsii). The prevalence of this particular soilborne disease resulted in more than 80% of dead plants in nongrafted tomato plots within the first 2 weeks of fruit production, whereas the use of resistant rootstock extended fruit production for 7 weeks. Similarly, recent studies on cost–benefit analyses of grafted watermelon (Taylor et al., 2008) and heirloom tomato production (Barrett et al., 2012b) indicated that using grafted transplants could be cost effective in the fields with high populations of soilborne pathogens and root-knot nematodes.

Table 5.

Comparisons of estimated gross returns; costs of transplants, harvest, and other production and operations; and total net returns between field production of grafted and nongrafted ‘Florida 47’ tomato in Live Oak, FL.

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Sensitivity analyses.

Overall, the change of net returns was dependent on the cost of grafted transplants and the tomato selling prices. For example, in the case of ‘Florida 47’ plants grafted onto ‘Beaufort’, with the marketable fruit yields achieved in 2010 and the tomato price of $8.95 per 25-lb carton, net returns became negative when the grafted transplant cost was $0.43/plant or higher (Table 6). In contrast, if the cost of grafted transplants was reduced to $0.34/plant, the net return was $368.38 per acre. When ‘Multifort’ was used and at the same tomato selling price, the net return remained negative even with the grafted transplant cost at $0.34/plant (Table 6). It should be noted that with the market tomato price of $8.95 per 25-lb carton, the nongrafted tomato production also led to a negative net return of $1680.62 per acre in 2010 using the estimated transplant cost of $0.15/plant in this study. These results clearly indicate that the financial competitiveness of commercial tomato production could be at risk when the tomato selling price is fixed at $8.95 per 25-lb carton or below, regardless of the type of transplants used. However, with the tomato price of $13.95 or higher, grafting with either rootstock would result in consistently higher positive net returns than nongrafted tomato production even when the grafted transplant had a cost of as high as $0.84/plant. As the grafted transplant cost decreases and/or the tomato selling price increases, the margins of net returns of grafted tomato production relative to the nongrafted plants would increase accordingly (Table 6). In addition, the net return was also sensitive to the level of marketable yields achieved. In the 2011 season, with higher marketable yields than in 2010, greater differences in net returns between grafted and nongrafted tomato production were observed. When the tomato selling price was $10.95 or higher, grafting with vigorous rootstocks led to consistently higher net returns than nongrafted tomato production even when the grafted transplant cost was the highest at $0.84 (Table 7). When negative net returns occurred for nongrafted tomato production at the tomato selling price of $8.95, using grafted transplants could reduce the loss of net returns when the transplant cost was at $0.67/plant or lower. For example, at the transplant cost of $0.54, the increase in net return as a result of grafting was $1316.51 and $1137.60 per acre with ‘Beaufort’ and ‘Multifort’, respectively (Table 7).

Table 6.

Estimated net returns of field production of ‘Florida 47’ tomato grafted onto ‘Beaufort’ (FL/BE) and ‘Multifort’ (FL/MU) and the differences in net returns between grafted and nongrafted ‘Florida 47’ (FL) production with varying tomato prices and grafted transplant costs using the 2010 yield data.

View Table

Table 7.

Estimated net returns of field production of ‘Florida 47’ tomato grafted onto ‘Beaufort’ (FL/BE) and ‘Multifort’ (FL/MU) and the differences in net returns between grafted and nongrafted ‘Florida 47’ (FL) production with varying tomato prices and grafted transplant costs using the 2011 yield data.

View Table

Furthermore, estimations of the break-even prices of grafted transplants at which grafted and nongrafted tomato production would lead to the same net return ranged from $0.56 to $1.25 per plant in 2010 (Table 6) and from $0.74 to $1.39 per plant in 2011 (Table 7). Theoretically, these values represent the maximum cost of grafted tomato transplants that a grower will accept to use grafted transplants. Overall, these break-even prices of grafted transplants increased with the increase in tomato selling price. Practically, it indicated that with the rising market tomato price, growers could be more willing to bear a higher cost of grafted transplants to obtain a higher net return in comparison with the nongrafted plants.

Although the high cost of grafted transplants remains the main barrier for wide adoption of vegetable grafting in the United States, results of this study in fumigated field in sandy soils showed that using grafted transplants is an economically viable practice that commercial tomato growers could potentially incorporate into their current production system. The margin of profit of grafted tomato production relative to nongrafted tomato production is more pronounced in the scenarios of reduced grafted transplant costs and increased selling prices for tomato fruit. In this study, tomato fruit size was not considered in the profitability analysis, which may deserve further assessment as grafting also led to an overall increase of average fruit weight (Djidonou et al., 2013). The fluctuation of tomato selling prices is oftentimes unpredictable; however, with research and technology advancement, it is expected that the cost of grafted transplants may be lowered in the near future. On the other hand, possible cost savings associated with grafted tomato production need to be fully evaluated. For instance, planting density may be reduced when using vigorous rootstocks given the yield improvement potential of grafted plants. According to Ricárdez-Salinas et al. (2010), with the use of grafted melon plants with no soil fumigation, planting density may be reduced by up to 60% as compared with nongrafted melon production with soil fumigation without compromising fruit yield. Limited information is available at present concerning the effect of grafting on plant population adjustment for cost reduction with different rootstocks.

In our study, the comparison of grafted and nongrafted tomato production was conducted in soils fumigated with 1,3-dichloropropene + chloropicrin, which allowed for evaluation of the grafting benefit for yield improvement beyond disease control. To provide a more complete analysis of economic feasibility for field production of grafted tomato, production systems with and without soil fumigation can be included in future studies that will help elucidate the economic returns associated with the effectiveness of disease control vs. improvement of crop vigor and yield enhancement.