Nowadays, the average life span of a corn, soybean, or alfalfa variety is 3-4 years. This does not give you a lot of time to look at a variety before it is being replaced by something that should be better. To make the right choice, you must use as much data as you can.
Normally there is a lot of data available. Each seed company should have research data, dealer test plots and in field results available; in addition to state, county and independently run trials. But while there is a lot of data available some data is worthless unless used with caution. Let's take a look at each type of data:
Research Data: Companies with research programs do small plot testing putting thousands of varieties per location for evaluation. The locations are scattered throughout the selling area of the company in hopes of representing average soil types and environmental conditions. Research sites tend to be pampered more and because of spacing between varieties tend to yield higher then a conventional field or test plot.
What do research plots show? Research plots show improvement over company's current varieties and they also give you an extra year of data on a variety.
What to watch out for: Where research plots are is the key thing to keep in mind. Some companies place their research on only the finest soil in an area, which is not always the case for your farm. Also watch out for research plots being far removed from you location, especially north or south. Corn and soybean performance is heavily dictated by maturity so looking at 10 plots a hundred miles south of you is of limited value.
Dealer Test Plots: Are strips of 5-40 varieties planted and run by a local dealer. Sometimes these plots have experimentals and competitive products.
What do dealer plots show? More localized results and plots under many different management and soil conditions.
What to watch out for: When there are competing varieties in a test plot I would ignore the results unless you trust all the people involved with planting, maintaining and harvesting the plot. Remember most people running these plots have a financial stake in seeing their products come out on top. It will be more accurate to compare one company's varieties to its own in plots like these. Watch also for poor spots in the field that can affect yield drastically.
Dealer In-Field Results: same as dealer test plots.
State, County And Other Independent Testing: Are yield trials run by state, universities and other 'independent' organizations. Most trials are set up like research plots.
What do state, county and independent testing show: Most unbiased way to show competing varieties against each other.
What to watch out for: Like dealer plots you must ask are these plots truly 'independent'. County, bank and crop consultant may be independent but their plots may be being run by people who aren't. Another thing to watch is these plots tend to be big and so varieties are spread out and may benefit or be penalized for being in a certain part of the field. Most state trials use a LSD (least signigicant difference) rating to compensate for this variation. This is a measure of variation within the field. Any varities that have yields within this LSD range are considered to have similar yield perfromance.LSD should not be ignored when looking at these trials.
With all this data available, now what? You must sort through and evaluate the plots. You should be looking both at as many locations as possible and at local plots.
The first step is to look at overall performance of a variety. A variety that does well in a lot of plots over a wide variety of soils and locations is one that shows a good agronomic package and should perform under a wide spectrum of conditions. The more plots you can look at, the better, even if they are not nearby. When looking at overall performance don't forget to look at different years if available. This is because weather probably has the biggest effect on a products performance. It is nice to look at hot years and cool year, wet years and dry years, to see what a product is doing. A variety may rule all its plots one year but the next it may look pretty average.
After you looked at all the plots then you should look at the plots close to you (within 50 miles). Try to look at plots with similar soil types, disease concerns and fertility levels. A variety's adaptation to any special requirements of your farm can only be determined by local results.
It is important to give consideration to both local results and all plots in all locations. Local plots will show if the variety can do the job in your area while the other plots will show how consistent a variety is and what should be its overall performance. The biggest mistake I see is when people put all the emphasis on only one year of results from local plots.
Don't be afraid to ask for data from your seed company. If your seed company can't provide you with research, local and state trial results don't waste your time, because you are going to need all of them to pick the right varieties for your farm.
My last words of advice on variety selection are to spread your risk and use several varieties (from the same seed company to assure genetic diversity). No matter how good a variety is, it is not going to be top dog every year under every condition. Using two or three varieties will help protect you from environmental conditions.