EXPEEIMENTAL WORK WITH EAW EOCK PHOSPHATE. 27 



creased where it is applied in conjunction with commercial forms 

 of nitrogen and potash. 



NITMBEE AND DISTRIBUTION OF PLOTS. 



It has been pointed out by various investigators that a very much 

 clearer and more accurate knowledge of the value of fertilizer treat- 

 ments can be gained by employing on a limited area many small 

 plots, repeating each fertilizer treatment as well as the checks on sev- 

 eral well distributed plots, than on the same area where larger plots 

 but fewer duplicates are employed. 



Piper and Stevenson^ state that a long period of experimentation 

 as well as the replication of plots tends to reduce probable error. 

 Mercer and HalP in summing up the results of an investigation on 

 " Errors of Field Experiments," state that in field trials the error 

 diminishes with increasing size of the plot, but the reduction in error 

 is small when the plot is above one-fortieth acre. These authors 

 recommend that in any field experiment each unit of comparison 

 (variety, method of fertilizing, etc., according to the object of the 

 experiment) should be given five plots of one-fortieth acre each, sys- 

 tematically distributed within the experimental area. Lyon ^ con 

 eludes that an area of one twenty-fifth acre of land, in four widely 

 separated plots, devoted to any one test, secures a much greater de- 

 gree of accuracy than the same area of land in one body. Olmstead * 

 states that the replication of plots is a great satisfaction both to 

 the experimenter and the readers of the literature, since it enables 

 both to determine whether the results show any valid conclusions 

 by giving them a means to estimate the precision of the work. 



Whitney ^ states, " It is obvious that if the range of the yields 

 of the different fertilizer plots among themselves is no greater than 

 the range of the yields of the check plots among themselves, the 

 relative effect of the different fertilizers would have no practical sig- 

 nificance. Very rarely are there duplicates of any fertilizer treat- 

 ment, and this is a weakness of the system. There are admittedly 

 wide variations in the yield of check plots, and to determine the real 

 yield under fertilization, it is just as important to have eight or ten 

 duplicate fertilizer plots as it is to have that number of duplicate 

 check plots." 



1 standardization of Field Experimental Methods in Agronomy. Proc. Am. Soc. Agron., 

 2, 72 (1910). 



» Experimental Error of Field Trials. Jour. Agr. Sci., 4, pt. 2, 107-127 (1911). 

 •Experiments to Estimate Errors. Proc. Am. Soc. Agron., 3, 114 (1911). 



* Some Applications of the Method of Least Squares to Agricultural Experiments. Jour. 

 Am. Soc. Agron., 6, 202 (1914). 



* Unpublished work. 



