INTERPRETING THE VARIATION OF PLAT YIELDS. 1 



By F. D. Farrell, Agronomist, Office of Western Irrigation Agriculture. 



FACTORS OF ERROR IN FIELD EXPERIMENTS. 



All results obtained in field experiments are subject to errors the 

 extent of winch can not always be accurately determined by physical 

 measurements. These errors may be due to a large number of causes, 

 such as incorrect weighing of crop products, faulty determinations of 

 plat areas, variations in the quantities of products recovered and 

 wasted, unobserved variations in field treatment, etc. These are 

 termed experimental errors, and the influence of some of them can be 

 determined and controlled. Other important causes are individual 

 plant variations, soil irregularities due to natural conditions or to 

 nonuniform previous treatment, uneven distribution of soil moisture, 

 temperature variations, etc. The influence of these factors can sel- 

 dom be accurately determined or controlled. Frequently the total 

 effect of all these causes is so great as seriously to influence the conclu- 

 sions drawn from observed results, and if it is not taken into con- 

 sideration the results may be badly misinterpreted. Where a large 

 number of observations are made of results obtained under condi- 

 tions winch are uniform, except as they are affected by accidental 

 error, the extent of that error can be calculated by a mathematical 

 formula, and a part of the calculation results in what is known as the 

 "probable error." 



EXPERIMENTAL DETERMINATION OF THE PROBABLE ERROR. 

 FIELD TESTS IN NEBRASKA AND MONTANA. 



In order to determine as nearly as possible to what extent these 

 factors would influence the crop yields of plats to be used in the field 

 experiments under irrigation at the Scottsbluff (Nebr.) and Huntley 

 (Mont.) experiment farms, certain of the fields to be used were 

 planted to uniform crops and given uniform treatment. In 1911 

 field K, at Scottsbluff, containing 66 quarter-acre plats, and field K, 

 at Huntley, containing 68 quarter-acre plats, were planted to oats. 

 At Huntley in the same year fields B II and B III, which are adjacent, 

 and which contain 46 quarter-acre plats, were planted to sugar beets. 

 In 1912 fields B II and B III, at Huntley, were planted to alfalfa. 

 Ten adjacent quarter-acre plats were planted to alfalfa in 1912 in 



1 Issued Jan. 4, 1913. 

 [Cir. 109] 27 



