Relationship Between Mean Square Errors and Wheat Grain Yields in Long-Term Experiments.

When yield data from field experiments are combined, the impact of environment on

treatment is ignored. The objectives of this work were to determine the frequency for

combining year to year data. Grain yield mean square errors (MSE) were calculated by-year

from two long-term winter wheat experiments (E222 and E502). These trials have been

continuously planted to winter wheat (Triticum aestivum L), and both annually receive different

nitrogen (N), phosphorus (P) and potassium (K) fertilizer rates. Relationships between average

grain yields, coefficients of variation (CV) and MSE were evaluated over 42 and 41 years for

E222 and E502, respectively. The F-statistics (large MSE/small MSE, 39dfn, 39dfd, alpha=0.10)

computed from two and three consecutive years were consistently more than the minimum Fvalue

required to combine sites. For 83 site years of data, combining any two or three

consecutive year-periods was not advisable. Individual years should be analyzed and reported

on independently