. Proceedings of the American Society of Agronomy . ll by months varies considerably in the different years, it isapparently the total quantity which fell during the period from Mayto August inclusive that determined the relative yields of the types ofmaize under experimentation. The danger of drawing conclusions from variety tests conductedthrough a single season thus becomes apparent, and, as a series ofwet or dry seasons frequently continues for several years, the studyof weather conditions in connection with variety tests is evidentlyimportant. m Method of Drazving Conclusions From Variety
. Proceedings of the American Society of Agronomy . ll by months varies considerably in the different years, it isapparently the total quantity which fell during the period from Mayto August inclusive that determined the relative yields of the types ofmaize under experimentation. The danger of drawing conclusions from variety tests conductedthrough a single season thus becomes apparent, and, as a series ofwet or dry seasons frequently continues for several years, the studyof weather conditions in connection with variety tests is evidentlyimportant. m Method of Drazving Conclusions From Variety Tests. There are two ways in which varieties may be ranked in produc-tiveness after they have been tested a number of years, (i) Byaveraging the yields for all of the years tested and basing the relative 1 I 2 PROCEEDINGS OF THE AMERICAN SOCIETY OF AGRONOMY. standing upon the average yield. (2) By grading the varieties foreach year and basing the relative standing on the average rank. Take,for instance, the hypothetical case presented in Table XL. Fig. 5.—Influence of rainfall on the relative yields of large ear and medium ear varieties of corn. LYON : EXPERIMENTS TO ESTIMATE ERRORS. I I 3 Table XL—Methods of Grading Varieties. Variety. 1903. 1904. 1905. AverageYield. Rank byYield. Rank Basedon AverageRank. Yield. Rank. Yield. Rank. Yield. Rank. A 45 I 40 I 60 2 48i 2 I B 37 3 36 3 56 43 4 3 C 42 2 38 2 70 50 I 2 D 47 47 3 4 Variety C ranks first in average yield, but when graded accordingto average rank variety A stands first. This is owing to the factthat in a year favorable to high yields C yielded considerably higherthan A, but in less favorable years A showed greater ability to with-stand drought or other untoward conditions and yielded more. Doubt-less the variety which produces the most in a series of years is themost desirable, which being the case the rank according to averageyield appears to be the most satisfactory method. Variety D was tested only one year. If
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