JOM£ OF AGRICETDRAL ISEARCH 



Vol,. XIX Washington, D. C, Jui.y i, 1920 No. 7 



PRACTICAL UNIVERSALITY OF FIELD HETEROGENEITY 

 AS A FACTOR INFLUENCING PLOT YIELDS 



By J. Arthur Harris 



Collaborator, Office of Western Irrigation Agriculture , Bureau of Plant Industry, 

 United States Department of Agriculture 



INTRODUCTION 



With the development of a more intensive agriculture there must be 

 a wider use and a progressive refinement of the method of plot tests in 

 agronomic experimentation. Betterment of the method of plot tests 

 must be sought along two lines, (i) the perfection of biological technic 

 and (2) the more extensive use of the modern higher statistical methods 

 in the analysis of the results. 



In 1 91 8 Mr. C. S. Scofield, in charge of the Office of Western Irrigation 

 Agriculture, and Prof. E. C. Chilcott, in charge of the Office of Dry-Land 

 Agriculture, asked the writer to undertake an investigation of the 

 statistical phases of the problem of the accuracy of plot tests. The 

 present paper deals with one aspect only of the general problem, that of 

 the lack of uniformity of the experimental field. This is both the most 

 potent cause of variation in plot yields and the chief difficulty in their 

 interpretation. 



Many of the careful writers on field experimentation have noted the 

 existence of soil heterogeneity. Few have, however, sufficiently recog- 

 nized and none have adequately emphasized the importance of this 

 factor. 



The problem of field heterogeneity is twofold. First, some measure 

 of the amount of its influence upon crop yields must be obtained. Sec- 

 ond, some means of avoiding or of correcting for its influence must, if 

 possible, be secured. 



An exact measure of the influence of field heterogeneity, and not 

 merely a vague notion that it may influence experimental results, is the 

 first and most fundamental step in the closer analysis of the factors 

 determining the variability of plot yields. If the application of such a 

 criterion to results obtained by practised agriculturalists from fields 

 selected for their uniformity shows no evidence of heterogeneity, plot 

 ^ tests may be carried out along conventional lines with confidence that 



Journal of Agricultural Research, Vol. XIX, No. 7 



Washingfton, D. C. July i. lyao 



urn Key No. G-196 



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