Source: UNIVERSITY OF FLORIDA submitted to
SUSTAINABLE VEGETABLE PRODUCTION SYSTEMS FOR SOUTH FLORIDA BASED ON USE OF COVER CROPS, PRECISION IRRIGATION AND CHEMICAL SOIL STERILANTS
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
TERMINATED
Funding Source
Reporting Frequency
Annual
Accession No.
0192495
Grant No.
(N/A)
Project No.
FLA-HOM-03998
Proposal No.
(N/A)
Multistate No.
(N/A)
Program Code
(N/A)
Project Start Date
Jun 1, 2002
Project End Date
May 31, 2007
Grant Year
(N/A)
Project Director
Klassen, W.
Recipient Organization
UNIVERSITY OF FLORIDA
BOX 100494, JHMHC
GAINESVILLE,FL 32610
Performing Department
TROPICAL RESEARCH & EDUCATION CENTER, HOMESTEAD
Non Technical Summary
Use of methyl bromide in vegetable production will be phased out by 2005. Cost of vegetable production must be lowered substantially to meet competition under NAFTA. The purpose of this project is to develop biologically based production systems, which allow Florida growers to compete strongly under NAFTA without the use of methyl bromide.
Animal Health Component
50%
Research Effort Categories
Basic
25%
Applied
50%
Developmental
25%
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
1021460102025%
2121460112035%
2131460114020%
6011460301020%
Goals / Objectives
1. Develop practical and reliable procedures for using methyl iodide, VAPAM or KPAM as a soil sterilant in production systems for tomato and pepper. (This will preserve tomato production in Miami-Dade County in the short term 2. For the long-term develop sustainable production systems for tomato, pepper and potato each based on use of nematode- and pathogen-resistant cover crops instead of chemical soil sterilants. One type of system will incorporate the cover crop into the vegetable beds under plastic mulch. The second type will utilize organic mulches derived from cover crops. Also increase profitability by folding in production of certain relay crops such watermelon, squash, cucumber, etc. 2a. Develop crop rotations and other weed management schemes that build down weed species that are hosts of the nematodes and pathogens of interest. Thereby, cause all of the nematodes and pathogens to die out or be reduced to inconsequential levels. 2b. Improve the management of cover crops to assure copious biomass production, desired crop residue mineralization rates and economical seed production. Develop use of desiccants for velvet bean and sunn hemp to facilitate harvesting of seed. 2c. Develop practical weed suppression technologies for cover crop production (especially weeds that are nematode hosts), and for rescue treatments in production of tomato with organic mulches. 2d. Genetically improve cover crops. Select sunn hemp germplasm that is adapted to Florida, and develop a production system for optimizing seed production and mechanical harvesting. Identify or select lines of velvet bean well suited to be used as a nematode-suppressant cover crop. Determine whether some of the nematode-resistant cowpea cultivars with valuable horticultural traits can serve both as cover crops and valuable cash crops. Develop the use of perennial Arachis for permanent beds and ground covers in groves. 3. Conduct research to reliably increase tomato yields in the order of 2-fold through science-based management of irrigation, fertigation and improvement of soil quality. Adapt the use of switching tensiometers to automatically maintain the optimum moisture level in the root zone and prevent leaching of fertilizer, and to measure leaching during and following high rainfall events by means of automated drainage lysimeters, especially in beds covered with organic mulches. 4. Conduct economic analyses of alternative production systems, determine social or economic constraints to adoption of advantageous systems, and identify appropriate measures to facilitate adoption if warranted.
Project Methods
Objective 1. Optimize KPAM treatment and methyl iodide treatment, through replicated, randomized complete block experiments with MC-33 as the standard of comparison. Develop use of halosulfuron-methyl as a rescue treatment. Objective. 2. Validate and optimize prototype tomato production systems, through replicated randomized complete block experiments involving: (A) Standard practices: (1) low level irrigation, (2) plastic mulch for weed control and (3) low level of compost, (B) Variables: (1)sorghum Sudan hybrid, (2) velvet bean, (3) fallow, (4) sunn hemp and (5)nematode-resistant cowpea. Yields may be compared to those produced by chemical alternatives. Use pot studies to determine the mechanisms whereby certain cover crops suppress plant parasitic nematodes, soil borne pathogens and weeds. Plant watermelon or other cucurbits after tomato harvest. Challenge prototype production systems severely by inoculating the beds with Meloidogyne incognita and Rotylenchulus riciniformis. Objective 2a. Initially selective herbicides will be used to build down the reservoir of weed propagules in the soil. Highly nematode-suppressant graminaceous cover crops (rye, German millet, etc.) will be rotated with the above-mentioned legumes. Objective 2b. To determine the best planting date for maximizing seed production in sunn hemp and velvet bean, compare yields from various seeding rates at various dates after the fall equinox. Registered desiccants and defoliants will be evaluated. Objective 2c. Evaluate selective herbicides registered for use on legumes and on the various horticultural crops. Determine whether weed suppression of organic mulches derived from cover crops may be improved by covering them with various thicknesses of compost. Objectives 2d. Sunn hemp. Select several lines of sunn hemp with determinate flowering and seed set to facilitate mechanical harvesting, disease and insect resistance, and high biomass yields for organic mulches. Velvet bean. Characterize and compare the various lines available from diverse sources. Cowpea. Trial some of the nematode-resistant cowpea cultivars with valuable horticultural traits to determine if some can serve both as cover crops and valuable cash crops. Import seed of Cratylea argentea and of Arachis pintoi cv 'Porvenir'. Cratylea will be evaluated for use in vegetable production systems. 'Porvenir' will be evaluated, along with A. pintoi cv 'Amarillo' and two selections of A. glabrata selected for high pH soils, as a ground cover in tropical fruit groves. Objective 3. Conduct studies on use of switching tensiometers or solid state moisture sensors to maintain desired moisture levels and to prevent leaching of fertilizer from the root zone. Determine the extent to which N availability matches crop uptake, and investigate the effects of timely fertigation. Objective 4. The economic feasibility of prototype systems will be assessed continuously as they evolve. Specific social and economic constraints to implementation will be identified. The North American Vegetable model will be employed to assess the impact of the new technology with respect to revenues from various crop commodities in various States.

Progress 06/01/02 to 05/31/07

Outputs
OUTPUTS: A study was conducted to enhance the capacity of velvetbean to produce biomass and suppress weeds by interplanting it with a trellis crop. Velvetbean (Mucuna pruriens) and sunn hemp (Crotalaria juncea) have emerged as two of the best legume cover crops. It is important to ascertain how best to take advantage of the most favorable attributes of both velvetbean and sunn hemp in sustainable vegetable production systems. One approach is to grow a mixed stand of the two crops in which velvetbean predominates and sunn hemp serves as a companion trellis crop, and this was the main objective of this study. Two velvetbean lines, Line 5 and Georgia Bush, were used in this study. The trellis crops in this study were Yellow Sweet 74071BC sweet corn, a short statured hybrid grown commercially in Miami-Dade County and an unknown cultivar of sunn hemp; both were treated with Rhizobium. Each plot in the RCB design was 18 feet X 30 feet (5.49 m X 9.14 m) with 25 feet (7.62 m) between adjacent plots. The predominant weeds were purslane (Portulaca oleracea), Amaranthus spp. and Parthenium hysterophoru. 70 pounds of N per acre (72.68 kg per ha) of 6-6-6 granular fertilizer was applied. The treatments were (i) Line 5 velvetbean + sunn hemp, (ii) Georgia Bush velvetbean + sunn hemp, (iii) Line 5 velvetbean + corn, (iv) Georgia Bush velvetbean + corn, (v) Line 5 velvetbean only and (vi) Georgia Bush velvetbean only. The weight of the seed of the trellis crops was 10% of that of the velvetbean. Seeding was accomplished on May 23, 2008. Biomass samples were taken on July 30, 2008 or 68 days after planting. Trellis crop plant parts were manually removed from the velvetbean parts, so that the biomass of the velvetbean, corn and sunn hemp could each be measured in each sample. Fresh and dry weights were determined. The main observations/conclusions were as follows: (1) The two velvetbean lines and the sunn hemp were able to become well established in spite of very dense weed populations. During the first two weeks the velvetbean plants were chlorotic. Some of the corn plants died and had to be replaced with transplants. Eventually velvetbean lines alone or together with the companion trellis crops developed closed canopies and the purslane plants became etiolated. (2) Line 5 + sunn hemp exhibited the highest combined wet and dry weights, but these were not statistically greater than the corresponding weights of Georgia Bush and sunn hemp. (3) Georgia Bush planted alone produced insignificantly more biomass than Line 5. (4) Sweet performed badly. In contrast sunn hemp grew higher than 180 cm, served as an excellent trellis for both velvetbean lines, and contributed abundantly to biomass production.(5) The seeding rate of sunn hemp in this experiment was only 3.35 kg ha-1, yet its wet and dry weights when grown in combination with velvetbean equaled the corresponding weights of velvetbean. (6) Neither companion crop spurred biomass production of velvetbean.(7)Considerable savings can be realized by seeding sunn hemp along with velvetbean at ten percent by seed-weight of the velvetbean seeding rate. PARTICIPANTS: Dr. Inga Zasada is a nematologist/plant pathologist with the Agricultural Research Service, USDA, Corvallis, Oregon. She is interested in physiological and biochemical mechanisms whereby cover crops suppress plant parasitic nematodes. TARGET AUDIENCES: These findings should be of considerable interest to those concerned with sustainable agriculture. This includes soil scientists, agronomists, horticulturists, nematologists, weed scientists and extension specialists and county agents. These findings are relevant to scientists who seek to develop biological soil disinfestation as a full or partial replacement for the banned methyl bromide soil fumigant. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
The main finding is that sunn hemp seeded together with velvetbean in a seed-weight ratio of 1:10 results in an excellent mixture in which sunn hemp, which germinates and grows very rapidly, serves as a trellis for velvetbean to shade-out weeds and produced copious quantities of high quality biomass. Only 8-10 weeks are required to produce these highly beneficial results in the southern USA, provided that these cover crops are seeded from April through July. Only about 1,300 cumulative heat units are needed for the production of about 5 tons per acre (dry weight) of this excellent crop mixture. Growers farm in in areas where the first frost occurs in mid-November have 38 frost free weeks after April 1 to produce vegetable and field crops. Since many cash crops can be produced in 9 to 15 weeks, there is ample time in the annual growing season to include the sunn hemp-velvetbean cover crop mixture in the cropping cycle. Since these crops, strongly suppress weeds and plant parasitic nematodes, improve soil fertility and offset some of the high costs of chemical fertilizers, this cover crop mixture should be considered as a best management practice. This mixture could be produced annually for biological soil disinfestation, whereby organic material is incorporated into moist soil, irrigated via drip lines if necessary, and kept covered with airtight plastic mulch for about two weeks to create anaerobic conditions. Biological soil disinfestation is a strong candidate for the replacement of soil fumigation with methyl bromide-chloropicrin.

Publications

  • Klassen, W., M. Codallo, I. A. Zasada and A. A. Abdul-Baki. 2006. Characterization of velvetbean (Mucuna pruriens) lines for cover crop use. Proc. Fla. State Hort. Soc. 119: 258-262.
  • Klassen, W., I. Zasada and M. Codallo. 2008. Enhancing the capacity of velvetbean to produce biomass and suppress weeds by interplanting with a trellis crop. (Manuscript in preparation.)
  • Wang, Q., Y. Li, and W. Klassen. 2007. Applying biosolids to control soil nematodes. Vegetarian Newsletter, Horticultural Sciences Department, University of Florida. February 2007. 3 pages.
  • Wang, Q., R. Munoz-Carpena, Y. Li, and W. Klassen. 2007. Reducing irrigation rates for tomato better yields. Vegetarian Newsletter, Horticultural Sciences Department, University of Florida. February 2007. 3 pages.
  • Wang, Q., Y. Li, and W. Klassen. 2007. Summer legume cover crops conserving soil water and nutrients. Vegetarian Newsletter, Horticultural Sciences Department, University of Florida. April 2007. 3 pages.
  • Wang, Q., Y. C. Li, Z. Handoo, and W. Klassen. 2007. Influence of cover crops in rotation on populations of soil nematodes. Nematropica 37(1): 79-92.
  • Wang, Q., Li, Y., Klassen, W., and Handoo, Z. 2007. Influence of cover crops and soil organic amendments on okra (Abelmoschus esculentus L.) production and soil nematodes. Renewable Agriculture and Food Systems. 22(1): 41-53.
  • Wang, Q., Li, Y., and Klassen, W. 2007. Changes of microbial biomass of carbon and nitrogen with cover crops in a tomato field. Journal of Plant Nutrition, 30: 1-17.
  • Zasada, I. A., W. Klassen, S. L. F. Meyer, M. Codallo and A. A. Abdul-Baki. 2006 Velvetbean (Mucuna pruriens) extracts: impact on Meloidogyne incognita, Lycopersicon esculentum and Latuca sativa survival. Pest Management Science, 62: 1122-1127.


Progress 10/01/05 to 09/30/06

Outputs
Two studies were conducted in colaboration with Dr. Bielinski Santos, CGREC, to determine the efficacy of different herbicide combinations on nutsedge (Cyperus spp.) control in bell pepper and eggplant. The tested herbicides were napropanide + metolachlor, napropamide + trifluralin, and napropamide + trifluralin + metolachlor. A non-treated control was also included. At 4 and 7 weeks after transplanting, nutsedge plants that emerged through the polyethylene mulch were counted over the whole area of the experimental units (100 linear ft row/plot). The results indicated that in eggplant the combination of napropamide + trifluralin + metolachlor had the lowest nutsedge populations (<5 plants/ft2) and highest yields (37% more than the non-treated control and 31% more than napropanide + metolachlor, and napropamide + trifluralin). Results for bell pepper were inconclusive, but it appeared that the duration of action of the herbicides was not sufficient. In collaboration with Dr. Inga Zasada, ARS, we evaluated the combination of the pH-raising potential of N-Viro Soil (NVS) with nitrogen containing cover crops for plant-parasitic nematode management. The experiment was a split-plot design with NVS (20 dry t/a) being the main plots and the cover crops sunnhemp, velvetbean and sorghum/sudangrass or no cover crop being the split plot. Field trials were established on two soil types in south Florida. NVS was incorporated into soil to facilitate a rapid increase in soil pH. On a sandy soil (Pine Island Farm) soil pH increased to 11.2 after NVS amendment compared to 7.7 without amendment. On a Krome soil (TREC) soil pH increased to 11.3 after NVS amendment compared to 7.8 without amendment. This increase may have been enough to facilitate the rapid conversion of ammonium to ammonia. Ammonia is toxic to nematodes. In fact, one week after amendment the pH in both of these soils had decreased substantially to 9.3 (PIF) and 8.5 (TREC). Nematode suppression at mid-season was expressed as M. incognita eggs/g root. At TREC there was no treatment effect on root-knot nematodes but the initial populations were very sparse. At PIF, there appeared to be a reduction in nematode reproduction by NVS alone or in combination with cover crops and the control. Combining NVS and cover crops did not increase the efficacy of either management practice above that observed when each was applied alone. There were no significant differences in tomato yields at either site due to N-Viro application or cover crop treatment. Marketable tomato yield per 30.5 m of linear row ranged from 80 to 128 kg and 180 to 228 kg at PIF and TREC, respectively.

Impacts
Herbicide combinations have been identified that will enable eggplant growers whose field are primarily infested with nutsedges to forego the need to fumigate the soil. However for pepper a combination of herbicides with a more prolonged effect is still needed. Since methyl bromide alternative fumigants are likely to be quite expensive, the option of using herbicides in some circumstances will help growers compete. N-Viro Soil can be very useful in suppressing root knot nematodes. This management strategy can be incorporated into a southern Florida vegetable production system six weeks prior to vegetable planting. This time period will allow for a reduction in soil pH as well as disappearance of ammonia and will negate any negative phytotoxicity to vegetables.

Publications

  • No publications reported this period


Progress 10/01/04 to 09/30/05

Outputs
A three year-experiment was conducted at two locations near Homestead, Florida to evaluate the feasibility of using a biologically-based system for winter production of fresh-market tomatoes (Lycopersicon esculentum Mill.) in south Florida fields with light to moderate infestations of the root-knot nematode (Meloidogyne incognita [(Kofoid and White) Chitwood], and yellow nutsedge (Cyperus esculentus L.). The system consisted of a cropping rotation in which nematode-resistant cover crops [cowpea (Vigna unguiculata (l.) Walp. cv. Iron Clay), velvetbean (Mucuna deeringiana (Bort.), Merr.) and sunn hemp (Crotalaria juncea L. cv. Tropic Sun)] were followed by a nematode-resistant tomato (Lycopersicon esculentum Mill.) crop. There were two cover crop treatments (cowpea and velvetbean) and a standard methyl bromide/chloropicrin (MC-33) treatment in 2000/01. A third cover crop treatment using sunn hemp was added in 2001/02. In 2003/04, two cover crop treatments (velvetbean and sunn hemp), a fallow (no cover crop), and a MC-33 treatment preceded by a summer sorghum sudangrass cover crop were used. Biomass production by the velvetbean, cowpea, and sunn hemp crops averaged 14.8, 8.5, and 11.6 Mg per ha, respectively. Suppression of root-knot nematode (Meloidogyne incognita) by the cover crops could not be rigorously determined because of very low or low density nematode populations. Marketable tomato yields in all treatments and in all years were above average annual yields in Miami-Dade County. Yields were highest in 2003/04 because the crop was healthy and favorable prices encouraged eight harvests. In contrast, yields were low in 2001/02 due to a heavy infection by foliar pathogens. In 2000/01, there was no significant difference in extra-large fruit yield among the treatments but the MC-33 treatment had a higher yield of large fruits than the cowpea and velvetbean treatments, thus resulting in a higher total marketable yield than both cover crop treatments. The total marketable yield in the velvetbean treatment was next highest. In 2001/02, the cowpea treatment had a significantly higher yield of extra-large fruits than the MC-33 and the velvetbean treatments and significantly higher total marketable yield than all other treatments. In 2003/04, equal marketable yields in all fruit-size grades occurred in the sorghum sudangrass/MC-33, velvetbean, and sunn hemp treatments and these were significantly higher than in the fallow treatment. Economic analysis showed that all treatments resulted in positive net returns in all years. Returns in 2003/04 were the highest of all study years due to high yields and high market prices. Among the cover crops, sunn hemp produced the highest tomato yields and net returns of all treatments over the two years it was used.

Impacts
In 2000 Vansickle, Brewster and Spreen assessed the likely impact of the ban of methyl bromide on vegetable production in Florida, and they concluded that tomato production would cease in areas of southern Florida in which nematicides such as 1,3-Dichloropropene readily leach into the underlying aquifer. However this study shows that in the absence of a chemical fumigant the rotational use of pest-suppressive cover crops can facilitate profitable tomato production at least on some fields with Krome gravelly loam, which does not support rapid build up of root knot nematodes. However dense yellow nutsedge populations may build up on Krome soil, and the technology has not been evaluated against high nutsedge populations.

Publications

  • Abdul-Baki, A. A.W. Klassen, H. H. Bryan, M. Codallo, B. Hima, Q. R. Wang, Y. Li, Y.-C. Lu, and Z. Handoo. 2005. A Biologically-Based System for Winter Production of Fresh-Market Tomatoes in South Florida. Proc. Fla. State Hort. Soc. 118. (In Press).
  • Wang, Q., Y. Li, and W. Klassen. 2005. Influence of summer cover crops on conservation of soil water and nutrients in a subtropical area. J. Soil and Water Conserv. 60:58-63.
  • Wang, Q., W. Klassen, Y. Li, M. Codallo, and A.A. Abdul-Baki. 2005. Influence of Cover Crops and Irrigation Rates on Tomato Yields and Quality in a subtropical Region. HortScience 118. (In press).
  • Zasada, I. A., W. Klassen, S. L. F. Meyer, M. Codallo and A. A. Abdul-Baki. 2005 Velvetbean (Mucuna pruriens) extracts: impact on Melodogyne incognita, Lycopersicon esculentum and Latuca sativa survival. Pest Management Science. (In review).


Progress 10/01/03 to 09/30/04

Outputs
Allelopathy of cover crops. The plant parts (main root, secondary roots, main stem, branches, petioles, and leaves) of the 8 velvetbean accessions and sunn hemp were dried, ground into powder. Extracts of these materials are being bioassayed for allelopathy and for toxicity to the root knot nematode. To elucidate the various proposed mechanisms for nematode suppression by cover crops, sunn hemp, velvetbean and sorghum sudangrass were grown in microplots with ten gallons of Krome soil. In certain treatments root knot nematode populations were established by inoculation of okra or Rutgers tomato with J2 larvae. Subsequently the cover crops were grown for 12 weeks. Nematode population densities and FAME values were determined prior to growing the cover crops and after teminating them. Cover crop residues were measured and then incorporated into the soil, and some of the microplots were tarped with polyethylene, and all were allowed to sit for 6 weeks. Next Rutgers tomatoes were planted into each microplot. Root galling, nematode densities, FAME values, biomass and fruit yield will be determined. A companion study is being conducted in Pine Island sandy soil. A randomized block experiment showed that the cover crops, sunn hemp and velvetbean, but especially sunn hemp can improve tomato yield and the quality in the south Florida. In addition organic mulch, if applied in two consecutive years, can significantly improve tomato marketable yield and quality. In order to overcome the problem of excessive weed growth in organically mulched beds, S-metolachlor and Napropamide were sprayed onto the surface of the beds and watered in with 0.25 inches/acre just before the application of the organic mulch. Although this treatment greatly suppressed yellow nutsedge and most broad leaf weeds, oxalis and certain grasses escaped. However the latter could be suppressed by post-transplant application of sethoxydim and rimsulfuron.

Impacts
The tropical legumes, velvetbean and sunn hemp, when grown in rotation with cash crops, can be expected to improve soil properties, suppress weeds and plant parasitic nematodes, and result in higher cash crop yields. Elucidation of the modes of actions of cover crops is likely to lead to advances in the rational design of cropping systems. Organic mulches can increase tomato yields, and the problem of excessive weed growth can be met with certain herbicides.

Publications

  • No publications reported this period


Progress 10/01/02 to 10/01/03

Outputs
Evaluation of velvetbean accessions. We determined the biomass production by various velvetbean accessions, number of days from seeding to first flowers, and nature of flower production. Each plot was 10m long with 5 rows with 60cm between rows. Lines 1-7 were planted with 30 cm between plants within the row, and lines 8 and 9 were planted with 20 cm between plants within the row. The combined biomass (gms) from a 4.19 m2 sample from the center of the plot plus the vines and/or leaves growing out from the west end of the plot were as follows: Line 1 (7301), Line 2 (8810), Line 4 (7730, Line 5 (7004), Line 6 (5869), Line 7 (7172), Line 8 (3613) and 'Georgia Bush'or Line 9 (2605). Time from seeding to appearance of first flowers was 110 days for Lines 8 and 9, 125 days for Line 4, and 160, 167,133, 182, and 160 for Lines 1, 2, 5, 6 and 7. Only lines 4, 8 and 9 had determinate flowering. Effect of cover crops on okra yields. To evaluate the effects of sorghum sudangrass, sunn hemp and velvetbean on okra yields, 1.33 acres of each was planted in May 2003. Velvetbean germination was poor and skips were replanted in early June. After these cover crops had been terminated and incorporated into the soil, okra was planted. Okra fruit yields (gm/7.7m of row) from 24 harvests were 6150 for velvetbean, 5135 for sunn hemp and 4624 for sorghum sudangrass. Thus the okra yield in the velvetbean treatment was 30 percent greater than in the sorghum sudangrass yield. A nematode new to Florida was discovered in a tomato field near Tamiami Airport, Miami-Dade County. It is Melodogyne graminicola, a pest of rice and grasses in troipical countries.

Impacts
The tropical legumes, velvetbean and sunn hemp, when grown in rotation with cash crops, can be expected to improve soil properties, suppress weeds and plant parasitic nematodes, and result in higher cas crop yields.

Publications

  • Aref Abdul-Baki, A. A., H.H. Bryan, W. Klassen, Q. R. Wang, Y. C. Li, Y.-C. Lu and M. Codallo. 2004. Cover Crops as Alternatives to Methyl Bromide in Fresh-Market Tomato Production in South Florida. J. Sustainable Agric. (In preparation.)
  • Handoo, Z. A., W. Klassen, A. Abdul-Baki, H. H. Bryan, and Q. Wang. 2003. First record of rice-root nematode (Meloidogyne graminicola) in Florida. Journal of Nematology 35:342 (Abstr.).


Progress 10/01/01 to 10/01/02

Outputs
A two year-experiment was conducted at Homestead, Florida to evaluate use of biological alternatives to methyl bromide (MeBr) in growing fresh-market tomatoes (Lycopersicon esculentum, Mill.). The biological alternative system consisted of a cropping rotation in which the nematode resistant cover crops [cowpea (Vigna unguiculata cv. Iron Clay), velvetbean (Mucuna deeringiana) and sunn hemp (Crotalaria juncea cv. Tropic Sun)] were followed by 'Sanibel', a nematode resistant tomato cultivar in 2001 and `Leila' a nematode susceptible cultivar for 2002. The experimental design was partly planned to serve as demonstration plots and consisted of 70-m long strips each containing three raised beds per treatment. There were two cover crop treatments (cowpea and velvetbean) and a methyl bromide control treatment in 2001. A third cover crop treatment using sunn hemp was added in 2002. Harvested fruits were graded following Florida Tomato Committee Standards, and separated into extra large and total marketable. There were no significant differences in extra large fruits among the MeBr and the cover crop treatments in 2001. Yields of extra large fruits were higher in the cowpea and sunn hemp treatments than in MeBr treatment in 2002. Total marketable yield in 2001 was highest in MeBr and lowest in cowpea. Total marketable yield in 2002 was significantly highest in cowpea whereas, yields were similar in MeBr, sunn hemp and velvetbean. In both years, the percentage of extra-large fruits was very high and total marketable yields of all treatments were higher than average yields for South Florida. In comparing production costs between the MeBr system and the alternative cropping systems without MeBr, we factored in per hectare costs of $1,404 for MeBr treatment, $260 reduction in fertilizer cost, and $88, $66, and $220 for seeds of cowpea, velvetbean and sunn hemp, respectively. Growers experience an $8.22 production cost per 11.4-kg carton, and a grower may receive $10.00 and $9.00 per carton of extra-large and large fruit, correspondingly, thus making a net profit of $1.78 and $0.78 per carton of extra large and large fruit, respectively. Based on these values the net returns per ha in 2001 were $5813 for MeBr, $6019 for cowpea and $6782 for velvetbean; and in 2002, $3184 for MeBr, $5380 for cowpea, $4467 for velvetbean and $5138 for sunn hemp. It should be noted that the populations of root-knot nematodes in the plots were sparse, and the putative alternatives must be evaluated under more rigorous conditions.

Impacts
The cover crop treatments offer a viable alternative production system to MeBr, result in high yields at a lower cost than those of MeBr, and are safer to the environment.

Publications

  • Abdul-Baki, A. A., H. H. Bryan, W. Klassen, Q. R. Wang, Y. C. Li and M. Codallo. 2002. Cover crops as alternatives to methyl bromide in fresh-market tomato production in South Florida. J. Sustainable Agriculture. (in review)