496 



Journal of Agricultural Research 



Vol. XV, No. 9 



In rotations 21 and 25 manure was applied each year preceding the 

 potato crop, while in rotation 31 the manure was applied for the sugar- 

 beet crop which preceded the potatoes. The annual differences in yield 

 between the manured and unmanured plots are also shown in the tables, 

 together with the mean annual yield of the crop in each rotation and the 

 mean of the annual differences in yield. With each of the means the 

 probable error is given.* 



Table I. — Effect of manure on the yields of Irish potatoes at the Scoitsbluff, Nebr., Belle 

 Fourcke, S. Dak., and Huntley, Mont., field stations, igi2 to igij 



[The yields, differences, and means are expressed in bushels per acre] 

 SCOTTSBLUFK 



BELLE KOURCHE 



a No manurial effect on this crop. 



' The probable error of the mean as used in these tables is obtained by Merriman's formula 36, which is 



o.84532y 



Stated as follows: rop'= 



n-\n- 



In other words, the probable error is obtained by multiplying the sum 



of the departures from the mean by the quotient of n-Jn—i into 0.8453, where m equals the nimiber of yields 

 involved (Merriman, Mansfield, method of least squares, ed. 8. 1913). 



