Using variety trial results to select crop varieties

Once harvest is complete, many farmers are anxious to see the results of crop variety trials to make their selections for the coming season. University variety trials are highly regarded due to their unbiased nature, but private trials are also useful. Kathy Grady, SDSU Extension Oilseeds Specialist, recently wrote an article for iGrow.org, outlining how to use variety trial results: http://bit.ly/1zfkXYI/. Following is a condensed version of the article.

Evaluate as much yield data as possible when selecting a variety, looking at relative performance over many locations and years. Variety comparisons over three years and several locations are better than from a single year or location. Consistent performance of a variety over many environments is called “yield stability”. To determine if one variety is better than another for a given trait, use the least significant difference (LSD 5% or LSD 0.05) value at the bottom of each data column. The LSD value is a statistical way to indicate if a trait like yield differs when comparing two varieties. If two varieties differ by more than the indicated LSD value for a given trait, they will likely differ when grown again under similar conditions. When evaluating yield, look at as many trials as possible. Trial results from neighboring states are readily available and provide additional data on variety performance. It is unlikely that the environmental conditions of a single test will repeat in any future year. It can be valuable to heavily consider yield trial information from plots close to your farm if it is available.

The coefficient of variability (C.V.) listed at the bottom of the data table is a relative measure of the precision or reliability of a test. Generally, trials with low C.V. rates are more reliable for making variety choices than trials with higher C.V. rates. Trials with C.V. rates of 15-20% or less may be considered reliable.

Among varieties with similar yield potential, consider oil and/or protein content. Some markets pay a premium for oil or protein above a certain level, or discount or even reject crops below a minimum level. It generally does not pay to sacrifice yield for oil or protein content.

For many crops, later-maturing varieties generally produce higher yields than early varieties when seeded at normal planting dates. Maturity is particularly important if planting is delayed. In many cases of late seeding only an early variety will mature properly and exhibit its best yield potential and oil content.

Varieties often differ in their resistance to diseases or insect pests. If a crop is grown in a field with a known history of a particular plant pathogen or insect pest, a resistant variety should be selected, if available. Variety trial results often report a lodging score or percentage. A high lodging score may indicate weak stems, stem disease, insect damage to the stem or roots, or adverse weather conditions such as high winds.

Be sure to plant only high quality seed with good germination. Certified seed is recommended to assure varietal purity, seed viability, and freedom from pathogens and weeds. SDSU crop variety trials for eleven different crop species, going back several years can be found at: http://bit.ly/1gGBACu.