The effect of fertilizer on the length of winter wheat heads
1938
Cook, R.L. | Baten, W.D.
The effect of fertilizers on the length of winter wheat heads was determined by measuring large numbers of heads taken from field plats in 1935, 1936, and 1937. The significance of mean differences was shown by analysis of variance. The use of Shepherd's correction for grouped data is illustrated. A statistical study of the number of heads necessary to make a representative sample is included. From the measurements and calculations, the following conclusions were drawn: 1. The unfertilized wheat produced longer heads in 1935 than did the fertilized wheat. In 1936 the condition was reversed. During both years, fertilizer applications greatly increased the number of heads per foot of row. The number of heads per foot of row on the unfertilized soil was almost twice as great in 1935 as in 1936. Accordingly it is concluded that when crowding is not a factor, fertilizers may be expected to increase the length of heads of winter wheat, but when the stand is so thick that the greater number of heads as a result of the fertilizer causes crowding, the length of the heads may be decreased. 2. Some fertilizers produced longer heads than did other fertilizers. 3. No differences in the results were obtained by using Shepherd's corrections for grouped data. 4. The data obtained from the measurement of 100 heads picked at random from each bundle showed that samples of 100 heads were not truly representative of the entire population. 5. When 700 heads were measured from each bundle, the significant differences were approximately the same as when all the heads were measured. The number "700" was also theoretically checked by calculating "N" from the formula for "t."
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