Market Growers > Growing Info & Resources > Guidelines for Conducting Variety Trials

Guidelines for Conducting On-Farm Variety Trials

by Micaela Colley, Bulk Seed Representative

Goals:
Careful variety selection is critical to the success of any farm. Farmers have always experimented, trying different growing techniques and crops and continually refining their growing practices. Through years of experience most growers have identified favorite varieties that are planted annually. However, the current germplasm available, the growing conditions on any given farm and the demands of the market are constantly changing and conducting annual on-farm variety trials offers growers an opportunity to continually select the best varieties available for their particular system. In addition, with the recent USDA organic certification guidelines requiring growers to utilize organic seed when available it offers an opportunity to compare their current varieties with varieties available organically grown.

When conducting scientific trials researchers replicate the treatments (varieties) at least three times across the field in order to account for field variability. A single planting in the field is an observational trial that gives a look at a variety, but the varieties performance could be due to the conditions of that specific site in the field rather than due to real genetic difference. The growing season can be extremely busy and many growers may feel overwhelmed with incorporating replicated trials into production. Although replicating varieties in multiple locations in a field or across multiple planting dates creates a stronger evaluation, trying as many or few varieties as possible on any scale can be very useful even if it is just an observational trial. However results should be considered as a snapshot of the variety’s potential and possibly trialed more than once before making a final decision whether to incorporate in into production or drop it. Another possibility is to cooperatively share trials with nearby growers so that each farm benefits from looking at different varieties or different crops.

1. Include a Check Variety: Always include a familiar, standard variety (one you normally plant) in the trial. This provides a point of reference when evaluating the trial varieties and is useful to check if the current season’s conditions are abnormally affecting the crop. For example, if you always plant Red Ace beet and are looking at other red slicing beets then plant Red Ace to compare with the performance of the other varieties. Also, if the Red Ace, which normally is a good beet for you, doesn’t grow well because a particularly cool spring made it less vigorous then you know that if the trial varieties also didn’t do well it was probably due to the conditions rather than the varieties true potential.
2. Variety Selection: When choosing varieties to trial it can be helpful to first identify the trial objectives. Are you looking for new varieties to expand your crop diversity? Is there a need for a variety that meets a certain challenge like pest or disease resistance, frost tolerance, or heat resistance? Or is the goal to find good organically available varieties? Once the objectives are identified then varieties may be chosen that have been recommended for your criteria. For example if you have really hot summers and want to grow lettuce all summer then you may start trying varieties described as having good bolt resistance.
3. Consistent Treatment: From seeding to harvest keep all treatments and inputs equal as much as possible. This prevents differences observed between the varieties resulting from differences in growing conditions rather than genetic differences. For example, all varieties should be sown on the same date, in the same potting soil, in the same greenhouse and transplanted at the same time. Likewise, inputs like irrigation and fertilization should be kept consistent. For example, if you switch your potting mix and half of the varieties were started in a more fertile mix they would have an unfair advantage and may appear more productive and healthier in the field because they got a better start rather than because they were really more vigorous varieties.
4. Field Location: Trials should be planted in a uniform area of the field to minimize variability in planting conditions between varieties. The best location would be one where soil type, irrigation, sun exposure, and temperature conditions are as uniform as possible. Additionally avoid planting trials on the edge of a field as conditions on field edges tend to be highly variable. For example, if you are trialing different varieties of broccoli and looking for the largest, most productive plants and one variety happens to be planted in a part of the field with the richest soil it may appear more productive due to the higher fertility conditions of where it was planted.
5. Trial Practicality: Paying attention to a trial and evaluating the results takes time. A practically scaled trial will bring greater success than trying so many varieties that many get overlooked.
6. Mark the Trial: Make sure that trial varieties are identifiable through the season. Planting tags are useful to mark varieties, but it is also a good idea to draw a map after planting since tags often get lost, run over, or fade in the sun.

Observational Trials: When varieties are grown in one location of the field and evaluated it is considered an observational trial. Observational trials can be very useful, especially if the above guidelines are followed, but their limitations should be kept in mind. Because conditions such as soil type, sun exposure, or irrigation may vary across the field there is a risk that differences in performance of varieties are due to variable field conditions rather than due to genetic or seed quality differences. We have all seen uneven irrigation or changing soil types resulting in variable plant growth across a field. Replicating helps account for this sort of variability. The benefits of observational trials over replicated trials are an ability to evaluate a larger diversity of material and greater ease and simplicity in planting.

Observational trials are useful for:

• An initial screening to evaluate whether a variety even merits consideration for commercial production.
• For evaluating the overall composition, or uniformity, of a strain of a variety in an adequately large population.
• As a quality control tool to check for trueness of type or other seed quality concerns.
• Identifying variety traits, or potential strengths or weaknesses of a variety, with consideration of potential field variability. This sort of information gains strength when replicated over time, over multiple locations, or is followed up with a replicated trial.

Replicated Variety Trials: In a replicated trial varieties are grown in what is called a randomized complete block design. Varieties are planted in blocks, or sections, across the field and each variety is grown in each block. Usually 3 or 4 blocks are used and the order that varieties are planted is randomized in each block. Replicating and randomizing increases the assurance that the differences measured or observed between the varieties is really due to genetic differences in the varieties rather that a result of field variability.

Replicated Trials are useful for:

• Evaluating critical variety characteristics particularly those easily affected by field variability such as yield, pest and disease resistance, vigor, bolting, cold and heat tolerance and plant size or growth rates.
• Comparing several sources of a variety to identify the highest quality source to use for future plantings.

1. Setting up blocks: First assess the anticipated field variability such as changes in soil type or sun exposure and then set up planting blocks (if possible) across the direction of variability so that there are greater differences in condition from block to block than within a block. For example:




Clay Soil	"Clayey" loam	Loam soil
Block 1	Block 2	Block 3

Decreasing amounts of clay in soil -------------------------->


2. Randomizing planting order of varieties: Each variety trialed should be planted once in each block. The order that they are planted in each block should be randomized. Randomizing the order helps prevent unanticipated biases in planting. For example, if three corns are being trialed and one is a particularly tall variety, and they are all planted in the same order in each block, then whichever variety is planted next to the tall corn may be unfairly stunted in each block by the shade of the tall variety. Planting order may be randomized by drawing names out of a hat, or mixing up planting stakes and choosing randomly or any other random method of selection. For example:




Block 1	Block 2	Block 3
A B C	B C A	C A B

Each letter represents a different variety planted in rows across the block. Each variety is planted in a different order in each block.


3. Evaluating Replicated Trials: When evaluating the varieties each replication should be looked at and considered as part of an overall evaluation. This helps take into consideration good or poor variety performance that may be due to variable field conditions. Researchers collect data from each replication and then assess the averages. They also statistically analyze how much variability there is between replications to calculate the level of assurance that the trial was a good evaluation.
4. Keeping Records: By keeping track of trial results from one year to the next results will be more meaningful over time. Identify what the key characteristics of importance are and take notes and measurements so that when you get ready for the next seasons trials you can remember which varieties held the most promise and should be tried again. We often only remember the very best and very worst from memory and many moderately performing varieties may be forgotten that might have performed better in another year.

There are a vast number of varieties available only certain number can be grown each year, but continually engaging in variety trials offers a chance to greatly increase your exposure to what is available. Conducting variety trials is an opportunity to see first hand which perform best for your system and your location and can be a great tool to increase your awareness of variety qualities. On several of our cooperating trial farms it is also an excellent learning tool for farm apprentices. Plant some new varieties this season and enjoy the process of discovery.