10 



CIRCULAR NO. 127. BUREAU OF PLANT INDUSTRY. 



plank being pegged Avitli the upper end 2 inches under water and 

 mth'a fall of 4 inches to its length. Carboys containing a weighed 

 quantity of acid were placed at the head of each plank with stoppers 

 arranged to drop the acid at a rate designed to empty the carboys in 

 six hours. A green-manure crop was plowed under on all the plats 

 m early spring. The acid applications were made at the time when 

 the tubers were beginning to fonn. The results are given in Table III. 



Table III. — Results of aridulation of irrigation water on potatoes at the Ddta Experi- 

 ment Farm in 19U. 



Rate of acid application per acre pounds . 



Stand per cent . 



Wilt do... 



Marketable yield per acre pounds. 



Unmarketable: 



Undersized per cent. 



Scabby do . . . 



Depth of plowing. 



12 inches. 6 inches. 12inches. flinches, 



500 



32.3 



58.0 



5,212 



13.4 

 10.6 



500 



31.4 



69.0 



5,992 



24.2 



900 



30.9 



64.0 



4,247 



IS. 5 

 9.4 



900 



36.8 



70.0 



5,622 



31.8 

 4.4 



While the results of acidulation show no increase in yield or 

 reduction in scab, they give other indications which are of interest. 

 These applications were made when the tubers were beginning to 

 form, so that the percentage of stand has no relation to the applica- 

 tion of acid. The immediate effect of the acid was a marked increase 

 in the vegetative vigor of the plants. This stimulation continued 

 during the remainder of the growing period, so that at harvest time 

 the haulm was double that of any other plats in the field. The wilt 

 infection on these plats was not only uniformly lower than on the 

 rest of the field, but the growth of the infected plants was much less 

 depressed. When the infected haulms on the rest of the field were 

 dead, the infected plants on the acid-treated plats w^ere still alive 

 and with a large portion of their total leaf area green. These results, 

 taken in conjunction with the lateness of the application, the moderate 

 \)v\ce of sulphuric acid, and the ease of application, suggest a prom- 

 ising field for further work. 



DEPTH-OF-PLOWING TEST. 



An experiment to test the effect of ])l()wiiig at varying (lc})ths was 

 conducted on field G. The plowing was done in March, the dei)ths 

 being 6, 12, and 18 inches. The potatoes were planted in June at a 

 uniform depth of G inches. Each part of the experiment was dui)li- 

 cated on quarter-acre plats, so that each result given in Table IV is 

 the average of two plats. 



[Cir. 121] 



