Long-time wheat variety yield comparisons
1944
Laude, H.H.
From the foregoing discussion it appears that comparative yields of wheat varieties in many instances do not continue constant during long periods of testing. In some cases the change in the comparative yield of varieties is gradual. Varietal differences may either increase or decrease during long periods of testing. The change in the comparative yields of varieties is assumed to be the result of changes either in the environment, including meteorological, biological, and nutritional factors, or in one or both of the varieties compared or in the environment and the varieties. If trend changes in the comparative yields of varieties are to be explained by environmental influences, it appears requisite that corresponding trend changes should prevail in the causal environmental factors. Varietal changes which may influence long-time comparisons must apparently be caused either by changes in the population of one or both of the varieties or by changes within the protoplasm of the plant of one or both varieties. The evidence is not conclusive as to where the causes lie which result in changes in relative yields of some varieties. Probably several causes are involved in different cases. Further research would appear to be desirable in the attempt to gain a better understanding of how and why comparative yields of varieties often do not continue constant for long periods of time.
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