By: Joseph G. Masabni and Frank J. Dainello
Vegetable trials are among the best educational tools available to Extension personnel—they should be an integral part of every agricultural county agent’s program. Field trials and demonstrations introduce new varieties, methods (Fig. 1), or concepts to local farmers. They also offer the county agent new opportunities to work closely with cooperating farmers, who are usually leaders in the community, as well as agricultural industry representatives.
For the best chances of success, county agents need to carefully choose the varieties to evaluate; select appropriate cooperating farmers to work with; establish the responsibilities of the agent and farmers; obtain seed, supplies, and equipment; establish the trial; make observations, take measurements, and take photos throughout the trial; and analyze and disseminate the results.
Limit the number of varieties or treatments in your demonstration. The number may depend on:
- The number of new varieties available in a particular crop
- The resources available, including land and harvest labor
- The frequency of harvest; for example, you may need to plant fewer varieties of a crop such as cucumbers or peppers (Fig. 2), which must be harvested several times a week, than once-harvested vegetables such as potatoes or carrots
In all variety evaluations, include the standard, recommended local variety as a basis for comparison with the newer varieties or breeding lines. The same holds true for concept demonstrations that compare local practices with the new techniques.
To allow enough time to acquire seed, choose the varieties to evaluate at least 2 months before the planting date. Request seeds of varieties that are known to produce well in your area. For help with variety selection, contact Extension vegetable specialists and seed company representatives. Ask them to prioritize the varieties in case you don’t have room or resources to try them all.
Get as much information as possible from the company about its seed, including germination percentage, seed treatments, and expected days to maturity. This data may influence your seeding rates or plot design. It may also explain any later problems in stand establishment or seedling vigor.
Farmers who participate in on-farm research are called cooperators. The success or failure of any field demonstration is closely related to the people selected to be cooperators.
A cooperator should be:
- Interested in the project
- Willing to contribute to the demonstration’s success
- An experienced grower, preferably of the vegetable to be evaluated
Work with as many cooperators as possible. They will enable you to evaluate varieties or concepts under different field and management conditions.
It is vital to clarify the responsibilities of both the agent and the cooperators before starting the trial. Draw up an agreement (next page) and have it checked by the county Extension director and/ or regional program director. Print the agreement on your letterhead, sign it, and have it signed by the cooperator. Deliver the agreement both orally and in writing.
Responsibilities of the Extension agent and the cooperator vary from one demonstration to another. In general, the Extension agent is responsible for:
- Obtaining seed or transplants
- Establishing the plots and giving the cooperator a field map and treatment codes
- Keeping yield and other records and observations
- Summarizing the data, preparing a report, and disseminating the information, making sure that the cooperators receive a copy of the report
- Coordinating field days and other activities related to the trial (Fig. 3)
The cooperator is generally responsible for providing land as well as management and maintenance inputs such as fertilizer, fumigation, mulch, weed management, and pest control.
The cultural methods for the demonstration plot should be the same as for the cooperator’s crop and in accordance with Extension recommendations.
Collect all seed and other supplies needed to conduct the trial at least 1 month before the anticipated planting date. Most seed companies are eager to cooperate in Extension trials by supplying seeds in exchange for receiving a written report of the results.
Hybrid seed is generally available from the developing company and associated dealers; open-pollinated varieties may be available from several sources. The major sources of vegetable seed are listed in the Vegetable Grower’s Handbook, which is available from the Texas A&M AgriLife Bookstore at https://agrilifebookstore.org/. Extension vegetable crops specialists can supply the names of specific people to contact at many seed companies.
For the trial to be a success, the seeds or transplants must be available in time to fit into the grower’s planting schedule. In many parts of the state, trials of transplants such as tomato and pepper entail more logistical problems than those of direct-seeded crops. A solution is to supply the seed for producing the transplants to the grower or to a producer of bedding plants.
Gathering supplies and equipment
Generally, demonstrations should not require expensive or elaborate equipment. Some items are necessary for most demonstrations (Table 1); others are specific to the vegetables being studied.
Most of these materials are available from several sources, including laboratory, forestry, or horticultural supply companies as well as local hardware, discount, garden, and farm supply stores. Occasionally, some pieces of equipment may need to be built to meet the requirements of the demonstration.
Establishing the trial
Demonstration trials should be conducted in season—that is, planted at the normal time for your area and the crop being evaluated. Finalize your plans well before the anticipated planting date. You’ll need to coordinate with the farmer in advance and continue communication throughout the planting.
The most accurate method for conducting trials is randomization and replication. Replications are repeated, independent plantings or treatment applications. Other than plantings for demonstration purposes, conduct all vegetable trials using this method. If the trial is set up properly, the statistical analysis of the data is more likely to be valid.
Replications: Determine the number of replications (reps) for your project according to the variability of the site conditions (such as differences in drainage or soil fertility), the type of treatment (such as a pesticide application), and the type of plants to be evaluated. More replications would be needed for crops that are planted far apart or that grow large, such as vining plants; fewer replications would be needed for crops planted closely or smaller plants, such as herbs. Generally, four reps are enough.
The unit of land where the varieties are planted is known as a plot. In a replicated trial, each replicate should contain a plot of the suggested size (Table 2) for each treatment. For crops not listed in Table 2, use the guidelines of similar crops; for example, the format for cowpeas would be like that for beans. Contact an Extension vegetable specialist for suggestions on crops that do not seem to fit these guidelines.
The procedures for trial establishment depend on the size of the cooperator’s operation and/or treatment limitations such as the amount of seed samples.
For small projects, mark out a representative plot of the required size that the cooperator will leave for you to seed or transplant by hand or with small equipment. It usually works best for the cooperator to plant the field and the demonstration area immediately afterward under your supervision.
For larger projects, where seed supplies are plentiful and the crop is planted mechanically, the plots can be seeded in rows with the cooperator’s equipment. After emergence, you can select uniform areas in the field for observation, yield, and other measurements.
It is harder to determine the number of plants to grow in each plot. For tomatoes and peppers, 8 to 12 plants per plot might be satisfactory; a bean plot might require a minimum of 60 to 100 plants.
It may be unrealistic to plan a replicated trial for vegetables that must be harvested often, such as okra and summer squash. For these vegetables, you may use single plots of each variety, with each plot being two or three times larger than the size suggested in Table 2.
The design used most often for trials is the randomized complete block. A block is a collection of plots, each with homogeneous plants and/or microenvironments. A block can have groupings of similar plants, treatments, or site conditions. The conditions within a block should be as homogeneous as possible; between blocks, there may be large differences.
Randomly assign the varieties or treatments within each block. Randomization ensures that each plant has the same chance of receiving any of the treatments. Begin the randomization process by arbitrarily assigning a code number to each variety or treatment (Table 3).
To simplify the procedure, draw up a blank field map depicting all replicates, with a slot for each treatment or variety entry. Table 4 is an example of a blank field map with four replicates.
Place each variety or treatment randomly within each replicate by using a computer-generated program, dealing playing cards, or dropping plot markers.
Computer-generated programs: Enter the code numbers into a form at Random.org (http:// www.random.org/), Research Randomizer (http:// www.randomizer.org/), or a similar site.
Playing cards: Each suit can represent a different replicate. Shuffle the cards well. As you deal them, place each number in a blank space on your field map (Table 5). Remember, always begin left and proceed to right.
- Identify all plots with plot markers.
- Label each marker with the replicate number and treatment number.
- Sort all like rep numbers into a bundle.
- Drop each bundle separately and pick up each marker randomly.
- Assign a spot on the map in the appropriate rep in the order that the marker was picked up.
For a field design to be valid statistically, each replicate must be adjacent to or touch another rep at some point, as must all treatments (plots) within each replicate. Always select uniform spots in a field large enough to accommodate all replicates of the test (Fig. 4).
To reduce variability and increase precision, include guard rows around the test plot area. A guard row is an extra row planted on both sides of the trial with plants like those in the test area. Plants on the borders of a plot may have access to more light, nutrients, or space for roots than the plants in the center of the plot. They also may be subject to more damage from insects, diseases, or wind. Guard rows reduce these border effects.
Consider allotting space at the beginning of the trial to be left unharvested to show to field day participants. These observation rows are especially useful for the plants of leaf and root crops that are destroyed during harvest.
Clearly mark all plots with large field stakes and flags. Smaller stakes and flags can disappear over the 3-month period of most trials. Create a field map showing the plots and surrounding areas, and give a copy to the cooperator.
During the trial, keep careful records of data on yield, plant height, days to first harvest, and other parameters specific to the crop being studied (Fig. 5).
For help in analyzing the data and advice on appropriate statistical analysis, contact an Extension vegetable specialist.
Take photos of plot establishment, plant emergence, transplanting, harvest, harvested plant products, and striking differences among varieties in performance or disease susceptibility. These photos will be extremely useful for future Extension meetings and publications.
Label the treatment or variety legibly. Prepare the labels in the office beforehand to ensure that they are available for photographing plots at the appropriate times.
Often the predetermined in-row spacing will not produce a perfect stand. If the varieties’ stands deviate greatly, your results and interpretations could be faulty. Therefore, always count stands and subject the results to statistical analysis. It is more meaningful to report the plant stands and actual yields rather than calculated yields based on a perfect stand. Calculated yields may be exaggerated because of reduced in-row plant competition.
Yields can be reported by plot, by acre, or by 1,000 linear bed feet (lbf). Plot yields provide a good comparison among the varieties or treatments being evaluated. However, there is some advantage in reporting acre yields instead, because they can be compared with grower yields or state average yields, which are expressed by acre.
Where wide-row cultural systems are used, it may be more useful to express yields per 1,000 lbf.
Disseminating the results
A trial is not complete until the report is written and the results are sent to the cooperator(s), the Extension vegetable specialist, and the seed companies that supplied the materials.
To disseminate the results further and maximize the educational and personal benefits of your demonstration trial, consider the following suggestions.
Conduct a field day to allow growers to study the varieties and/or concepts (Fig. 6). A successful field day will require good publicity, personal reminders to key growers, signs directing visitors to the field, well-marked plots, and field maps with treatment codes to distribute.
This type of meeting usually works best with only a brief introduction of what is being done and why, followed by self-guided tours through the plots. Be available to respond to questions, but allow the growers to evaluate the varieties for themselves.
Some light refreshments will help keep the growers around to discuss what they have learned and give you a chance for more interaction. The refreshments could be sponsored by a seed company or another agribusiness.
Contact the local farm newspaper editor, who may publish an article and/or photo graphs on the demonstration to inform growers who could not attend.
Include demonstration results in your county newsletter to give access to the results to those not at the meeting. It will also give all growers a record of the final results for their files.
The information in this publication was initially developed by Don Maynard, an Extension Vegetable Specialist at the University of Florida, and modified to meet the needs of Texas county agents.
Download a printer-friendly version of this publication: Guidelines for Conducting Extension Vegetable Trials
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