6 U.MVERsiTY OF Xkw IIami'Shire | Sta. Bull. 324 



seeding to oats, clover, and grass. Ordinarily no top-dressing was prac- 

 ticed on the Lane field either with manure or fertilizers ; hence the hay 

 crop usually "ran out" more quickly and had to be plowed sooner than on 

 the Jackson field. It will he noted, therefore, that the three-year rotation 

 under consideration in our experimental w-ork was somewhat shorter than 

 those previously practiced on the same fields. 



The primary purpose of these trials was to determine the efifects of 

 the three principal plant food nutrients on the growth of potatoes to find 

 out, if possible, whether any changes in the fertilizer formulae now on the 

 market should be made to increase yields or to lower production costs. 

 Accordingly, a 4-8-7 fertilizer was chosen as standard treatment and all 

 check plots received one ton of fertilizer per acre of this analysis. In the 

 first two courses of the rotation on the Jackson farm, potatoes were grown 

 without nitrogen and with double nitrogen in the 0-8-7 and 8-8-7 series, 

 withcnit phosphorus and with double phosphorus in the 4-0-7 and 4-16-7 

 series, also with no potash, limited potash and increased potash in the 

 4-8-0, 4-8-3 and 4-8-10 series. 



During the first two courses of the rotation on the Jackson farm, two 

 years' results are not included in the summary. The season of 1928 was 

 very wet at planting time and one section of the plots developed a very 

 poor stand of potatoes. Hence, the 1928 figures are not included in the 

 summary. During the season of 1933. a promising early variety of po- 

 tatoes was grown, but this variety behaved so dilTerently from Green Moun- 

 tains, the kind that had previously been produced, that it has been deemed 

 advisa])le to omit the 1933 data. They will be discussed separately, how- 

 ever. 



Table I is a summary, therefore, of four comparable years of the first 

 six in the Jackson farm trials. 



TABLE I. 4-year average yields of potatoes on the Jackson farm, 1929-32. 



N (n-1) from mean and n to the number of plots. 



In interprctinff probable error, we have considered that to be slRnificant, a difference must be at 

 least three limes its probable error. 



See H. H. Love, "The Role of Statistics in ARronomic Expe rimentation," .Sci. Acri. 5: 84-92. 



P. E. of the difference is calculated by the formula: -. /f P- K.l^ _|_ (P. E.)= where P.E. in each 

 case is the probable error of the individual determinations from which the difference is derived. 



In discussing the data in Table I, it seems desirable to state that a 

 great deal of work has been done by research workers and farmers on 

 the fertilizer formuhe, to attain the most desirable balance of nutrients as 

 well as to determine desirable amounts of plant foofl. 



