July i, 192 Universality of Field Heterogeneity 313 



between nitrogen content and carbon content of samples from two differ 

 ent soils is of the order -f 0.75. 



It is interesting to note that these coefficients for water content and 

 for chemical composition of the soil are of about the same order as those 

 found for crop yields. While these results do not prove that the hetero 

 geneity of experimental fields in their capacity for crop production is 

 directly due to these and other physical and chemical factors, there can 

 be little doubt that this is actually the case. 



The references here made to the existence of significant heterogeneity 

 in fields passed by agricultural experts as satisfactorily uniform must not 

 be interpreted as a criticism of the work of these investigators. There is, 

 indeed, every evidence of care and thoroughness. The result merely 

 illustrates the inadequacy of personal judgment concerning the 

 uniformity in physical characters or in crop-producing capacity of fields 

 under consideration for experimental work. 



The demonstration that the fields upon which plot tests have been 

 carried out in the past are practically without exception so heteregeneous 

 as to influence profoundly the yields of the plots emphasizes the necessity 

 for greater care in agronomic technic and more extensive use of the 

 statistical method in the analysis of the data of plot trials if they are to 

 be of value in the solution of agricultural problems. 



To other phases of the problem we shall return in subsequent papers. 



LITERATURE CITED 



(1) BATCHELOR, L. D., and REED, H. S. 



1918. RELATIONSHIP OP THE VARIABILITY OF YIELDS OP FRUIT TREES TO THE 



ACCURACY OP FIELD TRIALS. In Jour. Agr. Research, v. 12, no. 5, 

 p. 245-283, ii fig. Literature cited, p. 282-283. 



(2) COOMBS, G. E., and GRANTHAM, J. 



1916. FIELD EXPERIMENTS AND THE INTERPRETATION OP THEIR RESULTS. In 

 Agr. Bui. Fed. Malay States, v. 4, no. 7, p. 206-216, i fig. 



(3) HARRIS, J. Arthur. 



1913. ON THE CALCULATION OP INTRA-CLASS AND INTER-CLASS COEFFICIENTS OP 



CORRELATION FROM CLASS MOMENTS WHEN THE NUMBER OP POSSIBLE 



COMBINATIONS IS LARGE. In Biometrika, v. 9, pt. 3/4, p. 446-472. 



(4) 



1914. ON SPURIOUS VALUES OF INTRA-CLASS CORRELATION COEFFICIENTS ARIS 



ING FROM DISORDERLY DIFFERENTIATION WITHIN THE CLASSES. In 

 Biometrika, v. 10, pt. 2/3, p. 412-416. 

 (5) 



1915. ON A CRITERION OF SUBSTRATUM HOMOGENEITY (OR HETEROGENEITY) 



IN FIELD EXPERIMENTS. In Amer. Nat., v. 49, no. 583, p. 430-454. 

 (6) HASTINGS, S. H. 



1916. THE WORK OP THE SAN ANTONIO EXPERIMENT FARM IN 1915. U. S. 



Dept. Agr. Bur. Plant Indus. West. Irrig. Agr. 10 (Misc. Pub.), 17 p., 

 i fig. 

 (7) and BLAIR, R. E. 



1915. HORTICULTURAL EXPERIMENTS AT THE SAN ANTONIO FIELD STATION, 



SOUTHERN TEXAS. U. S. Dept. Agr. Bui. 162, 26 p., 8 fig. 



