Using crop performance tests – GREAT BEND TRIBUNE
As of Aug. 3 much of the central part of Kansas is still rated as abnormally dry. This past week’s heat should continue to intensify these dry conditions. Northwest Kansas ranges from abnormally dry to a small area of severe drought. The six to ten-day outlook (Aug. 11-15) indicates above normal temperatures and normal to below normal precipitation. The eight to 14-day outlook (Aug. 13-19) indicates more of the same. This isn’t good news for the dryland soybean and milo crops and some late planted corn.
Last week we discussed the replicated crop performance tests K-State and other institutions put out and how they differ from most strips put out by industry. Is this information useful? Yes, if you know how to interpret it and that holds true for company strip tests. So this week, how to interpret these tests.
• We are discussing replicated field trials that can be statistically analyzed, not the strip/demonstration tests companies put out. These may be somewhat useful but cannot be analyzed.
• Look for tests as near your area as possible which may be possible. Also try to find tests representing your soil type and where appropriate dryland and irrigated. Pay attention to all the cultural practices used from seed date and rate to crop rotation, fertility, and any special conditions that occurred.
• Where possible try to look at two or three year averages instead of just one year’s data. This may not be possible.
• You will find the individual cultivar average yields and an average for the trial. Often you will find the yields converted to a percent of the average yield which is often more valuable. This tells you how a cultivar did compared to the rest of the test more easily. Also pay attention to other information such as test weight, harvest moisture and if provided plant stand or head number.
Now to the statistics which aren’t hard to understand but need explanation.
• CV (%) – the CV, Coefficient of Variance gives you an idea of how much variation there was within the plots of a given cultivar in relation to the overall test average. In English it simply means how much variation there is across the plots of a given variety/hybrid. The larger the number, the more variation there was within the cultivar. A large number indicates less confidence should be placed in the values. In fact, when the CV is too large, results are often discarded.
• LSD (0.05) – this is the Least Significant Difference. Whatever the value, two varieties/hybrids must differ by more than this number for the values to be significantly different. Let’s say the number was ten bushels. Unless two cultivars differ by more than ten, they aren’t “statistically” different. It may seem backward but the 0.05 level means that 95% of the differences between cultivars is due to the cultivar, not some other factor. These are other LSD values such as 0.01 and 0.10. The trouble for a producer is that the difference at 0.10 (90% of the difference is due to the cultivar) may be important or even the 0.20 value but those aren’t given. They have been asked about providing those in the past but it hasn’t happened yet. This is where you may want to use your own judgement.
Dr. Victor L. Martin is the agriculture instructor/coordinator for Barton Community College. He can be reached at 620-792-9207, ext. 207, or firstname.lastname@example.org.