The yield potential of a given variety cannot be measured with complete accuracy. Consequently, replicate plots of all varieties are evaluated for yield, and the yield of a given variety is estimated as the mean of all replicate plots of that variety. Yields vary somewhat from one replicate plot to another, which introduces a certain degree of error to the estimation of yield potential. As a result, although the mean yields of some varieties are numerically different, the two varieties may not be significantly different from each other within the range of natural variation. That is, an ability to measure yield is not precise enough to determine that such small differences are other than what might be observed purely by chance.
The least significant difference (LSD) is an estimate of the smallest difference between two varieties that can be declared to be the result of something other than random variation in a particular trial. Consider the following example for a given trial:
Yield
Variety (bu/a)
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Abe 40
Bill 35
Charlie 31
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LSD 7
The difference between variety Abe and variety Bill is 5 bu/a (i.e., 40 - 35 = 5). This difference is smaller than the LSD (7 bu/a). Consequently it is concluded that variety Abe and variety Bill have the same yield potential, since the observed difference did not occur purely due to chance.
The difference between variety Abe and variety Charlie is 9 bu/a (i.e., 40 - 31 = 9), which is larger than the LSD (7 bu/a). Therefore, it is concluded that the yield potential of variety Abe is superior to that of variety Charlie, since the difference is larger than would be expected purely by chance.
The coefficient of variation (CV) is a measure of the relative precision of a given trial and is used to compare the relative precision of different trials. The CV is generally considered to be an estimate of the amount of unexplained variation in a given trial. This unexplained variation can be the result of variation between plots, with respect to soil type, fertility, insects, diseases, moisture stress, etc. In general, the higher the CV, the less precise a given trial is.
The coefficient of determination (R squared) is another measure of the level of precision in a trial and is also used to compare the relative precision of different trials. The R squared is a measure of the amount of variation that is explained, or accounted for, in a given trial. For example, an R squared value of 90% indicates that 90% of the observed variation in the trial has been accounted for in the trial, with the remaining 10% being unaccounted. The higher the R squared value, the more precise the trial. The R squared is generally considered to be a better measure of precision than is the CV, for comparison of different trials.
Within the Group IV trials, the wide variation in maturity dates is attributed to lack of rigid standards for classifying varieties within a group. It was decided to subdivide Group IV into 2 maturity groups. All maturity groups were assigned an early and late-maturity check. They were as follows:
Maturity Group Early Maturing Late Maturing
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Group IV Early ---- TN4-86
Group IV Late TN4-86 R 499
Group V R 499 P 9592
Group VI P 9592 P 9692
Group VII P 9692 ----