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JOURNAL OP AGRIOJITIAL RESEARCH 



Vol. XX Washington, D. C, December i, 1920 No. 5 



PERMANENCE OF DIFFERENCES IN THE PLOTS OF AN 

 EXPERIMENTAL FIELD 



By J. Arthur Harris, Investigator, Station for Experimental Evolution, Cold Spring 

 Harbor, N. Y ., and Collaborator, Office of Western Irrigation Agriculture, and C. S. 

 SCOFIELD, Agriculturist in Charge, Office of Western Irrigation Agriculture, Bureau 

 of Plant Industry, United States Department of Agriculture 



I.— INTRODUCTION 



Agronomists have long recognized the fact that the plots of an experi- 

 mental field may differ considerably among themselves. This varia- 

 bility is the source of the greatest difficulty in the interpretation of 

 comparative cultures. A recent analysis (j) 1 of the available data by 

 adequate biometric formulae (7) has shown that heterogeneity is a 

 practically universal characteristic of experimental fields and that it 

 must be considered in the interpretation of the results of all plot tests. 



With the demonstration of this characteristic of experimental areas 

 the questions naturally arise: Are the differences between plots tran- 

 sient or are they relatively permanent from year to year? Do these 

 differences tend to increase or to decrease with cultivation ? 



Presumably the differences which obtain in the soil of an experi- 

 mental field are in part permanent and in part transient. Lyon (5) 

 suggested that tillage and other factors will change the plots so that the 

 results will not be comparable from year to year. Unfortunately he 

 does not present data to show to what extent this may be true. He 

 gives a series of yields for successive years on the same plots, which 

 measured 33 by 66 feet or V20 °f an ac re in area, at the Nebraska Agri- 

 cultural Experiment Station and shows that the rank of the yield of 

 these plots differs greatly from year to year. Thus he concludes that if 

 they differ among themselves in their capacity for crop production this 

 difference is very little constant from year to year. 



Smith (6) took advantage of the breaking up of a piece of land which 

 had lain 16 years in pasture to investigate the effect of cultivation on 

 the uniformity of a series of plots. Any influence of 1 or 2 years pre- 

 ceding cultures on the variation or correlation of yields should, he 

 assumed, be apparent in the statistical constants deduced from these 

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1 Reference is made by number (italic) to " Literature cited," p. 356. 



Journal of Agricultural Research, Vol. XX, No. 5 



Washington, D. C. Dec. 1, 1920 



vr Key No. G-313 



2: (335) 



