2007 Annual Report for GS07-060
Potential of grafting to improve nutrient management of heirloom tomatoes on organic farms
Literature from Asia, the Mediterranean, and Morocco suggests that grafted, herbaceous plants may be more efficient at absorbing certain macro- and micro- nutrients (Ruiz, 1996: Leonardi, 2006) yet research to support these statements is scarce. The purpose of this project is to evaluate the nutrient uptake of grafted tomatoes compared to non-grafted tomatoes as well as to evaluate the productivity of an organic, grafted, heirloom tomato crop grown under a high-tunnel system as compared to an open field system.In order to take advantage of highly vigorous rootstocks used in grafting one must have an understanding of the total nutrients required for cropping systems as well as the critical times for nutrient applications.
Fertilizer inputs of nitrogen, phosphorus, potassium, calcium, and magnesium are often required in soil-based systems for tomato production. Supplying post-planting macro-nutrients to an organic tomato crop, commonly grown under plastic mulch and with drip irrigation, is a challenging task. Soluble materials that meet the National Organic Program (NOP) standards are limited and expensive. If grafted tomato plants are more efficient at taking up nutrients then a reduction of fertilizer inputs could possibly be incurred. Farmer’s profits could increase with reduced costs associated with fertilizer applications (i.e. labor, product) thus making their production system more economically sustainable. A reduction in fertilizer applications would also reduce the potential for leaching of nutrients into the water supply therefore contributing to regional groundwater protection.
This research project will evaluate grafted plant performance given multiple levels of post-plant nitrogen, compare the macro- and micro nutrient concentration of leaf tissue of grafted plants and non-grafted plants at various growth stages, and compare cultural management systems for grafted plants (i.e. planting date, pruning, trellising) in a high-tunnel and open field system. By combining cultural management practices with grafting technology, a sustainable systems approach to growing organic tomatoes will be developed for small growers of the Southeast. More and more farmers are interested in growing crops under high-tunnel structures as they recognize the multiple benefits tunnels can provide including: season extension opportunities, protection from extreme weather events, and a reduction of foliar disease pressure. Yet growing under high-tunnels comes with its own challenges, such as decreased ability to rotate crops, accumulation of fertilizer salts overtime, and increased potential for heat stress. Grafted plants may be uniquely suited to production in a high-tunnel environment due to their increased stress tolerances and disease resistance.
- 1) Establish nitrogen growth curves for grafted tomato plants. 2) Compare crop productivity and nutrient uptake of grafted heirloom tomatoes given different nitrogen inputs. 3) Assess the interaction between rootstock/scion combinations on crop productivity and nutrient uptake. 4) Compare the performance of grafted heirloom tomatoes in organic high-tunnel versus open field production. 5) Develop and disseminate research-based knowledge via workshops, extension publications, research tours, etc. that can be used by organic growers to successfully and profitably adopt this technology into their current growing practices.
In 2007, a greenhouse study was conducted at the North Carolina State University Phytotron research facility evaluating the tomato cultivars, Trust (Solanum lycopersicum) and German Johnson (Solanum lycopersicum), grafted onto the interspecific hybrid rootstock, Maxifort (Solanum lycopersicum x Solanum habrochaites). The plants were grown in pot culture and fertilized with a modified Hoagland solution twice per day post-transplanting. Total nutrient concentration of the leaf tissue was calculated for both macro- and micro- nutrients (leaf biomass x % nutrient concentration) and plant growth indicators were measured.
Shoot biomass, root biomass, and height of Maxifort-Trust and Maxifort-German Johnson grafts were significantly higher compared to the non-grafted treatments (P<0.01). The shoot biomass and height of the self-grafted treatments were also significantly higher for than the non-grafted treatments. The total macro- and micro-nutrient content of the leaf tissue of the Maxifort-Trust and Maxifort-German Johnson grafts were significantly higher for: N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, B than the non-grafted treatments (P<0.01). The total macro- and micro-nutrient content of the leaf tissue of the self-grafted treatments were significantly higher for: N, P, K, Mg, S, Zn, Cu, and B than the non-grafted treatments (P<0.01). There was no significant difference for total Na content among grafting treatments (P=.1288). Both scion varieties (Trust and German Johnson) showed similar effects from grafting across all plant growth indicators and leaf tissue nutrient content. The data from this experiment continues to be analyzed.
Systems Comparison Field Trial
In 2007, a trial comparing the performance of grafted and non-grafted heirloom tomatoes grown in a high-tunnel system compared to an open-field system was conducted at the Center for Environmental Farming Systems (CEFS) located in Goldsboro, NC. Both production systems were managed following the National Organic Program (NOP) guidelines. The tomato cultivar, Cherokee Purple (Solanum lycopersicum) was grafted onto two rootstocks, Maxifort and Beaufort (Solanum lycopersicum x Solanum habrochaites). Grafting significantly increased the cumulative total yield of fruit (lbs/A) in both the field and high-tunnel systems (P<0.05). The cumulative total yield of marketable fruit in the high-tunnel system was greater than that of the field system (P<0.05). Non-marketable fruit showed greater susceptibility to fruit cracking, blossom end rot, and cat-facing in the high-tunnel system but insect damage and tomato spotted wilt virus were lower in the high-tunnel system compared to the open field system (P<0.05). Three treatment levels of total nitrogen were applied to the each system at the following rates: 100lbs/A, 150lbs/A, and 200lbs/A. The rate of 150lbs/A (168 kg N/ha) produced the highest yields of fruit in both grafted and non-grafted plants under the high-tunnel system but did not show significant effects in the field system (P<0.05). The statistical analysis of the leaf tissue concentration data continues to be analyzed. This trial will be repeated in 2008.
On-farm Grower Cooperator Trials
Three trials were conducted at private North Carolina farms in 2007. Each trial evaluated two rootstocks and one scion which was chosen based on the grower’s market preferences (scion) and potential disease pressure (rootstock). Tissue samples were collected over the course of the growing season to assess the nutrient status of the crop at different growth stages. Yield information was collected by grower cooperators over the course of the season. This data is currently being analyzed. All on-farm trials will be repeated in 2008.
Impacts and Contributions/Outcomes
• National SARE ‘New American Farm’ Conference, Poster Presentation. “Grafting Rootstocks onto Heirloom and Locally Adapted Tomato Selections to Confer Resistance to Soil Borne Diseases and Increase Nutrient Uptake for Market Gardeners”. Kansas City, MO. March, 2008.
• Southern Region, American Society for Horticultural Science (S-ASHS) Graduate Student Poster Presentation, “Nutrient Uptake Efficiency and Plant Growth Indicators of Grafted Tomatoes”. Dallas, TX. February, 2008.
• CFSA Sustainable Agriculture Conference. Extension Track Conference Session 1, entitled ‘Connections: SARE and Current Research’ about Grafted Tomato Research. Durham, NC. November, 2007.
• Center for Environmental Farming Systems (CEFS) – ‘Tomato Grafting: Techniques, Benefits and Management Workshop’ October, 2007.
• CEFS Fall Festival, ‘The Use of Grafted Tomatoes in High Tunnels’ Presentation, September, 2007.
• Tomato & Melon Grafting Demonstrations for Dr. Mary Peet’s, Graduate Greenhouse Vegetable Production & Undergraduate Vegetable Production Classes – Spring/Fall 2007.
• CEFS: High Tunnel Research Tour, May 15, 2008.
• National Association of County Agriculture Agents Conference, key-note lunch presentation and CEFS high-tunnel research tour, July 13-17, 2008.
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