24 



BULLETIN 958, TJ. S. DEPARTMElsTT OF AGRICULTURE. 



eral use on the soils in question. After the crop had reached matu- 

 rity 400 hills of each crop were dug, the tubers counted, and the weight 

 for each hill obtained. The results are given in Table X. 



Table X. — Relation of soil type to the number and the weight of tubers as shown in tests of 

 tioo varieties of potatoes grotun under field conditions near Greeley, Colo., in 1918. 



Character of the soil. 



Triumph variety. 



Ntunber 

 of tubers 

 per hill. 



Weight of tubers 

 (grams). 



Per MU. Average. 



Rural New Yorker variety. 



Number 

 of tubers 

 per hUl. 



Weight of tubers 

 (grams). 



Per hill. Average. 



Heavy clay 



Clay loam^ 



Fine sandy loam 



3.1 

 4.2 

 5.9 



194.6 

 387.2 

 489.4 



62.0 

 93.3 

 83.3 



3.0 

 4.9 

 6.3 



376.7 



663.7 



1, 033. 6 



125.3 

 136.5 

 162.8 



The lowest production of tubers with respect to both number and 

 weight per hill was on the heaviest soil, while the highest numbers and 

 yields were produced on the lightest soil, indicating a tendency toward 

 an increase in the productivity of the plant as the character of the soil 

 changes toward the lighter types. Since these results cover only a 

 single season, it is possible that the relationships found to exist in 

 this experiment might be modified somewhat under different climatic 

 conditions as well as by differences in the relative state of produc- 

 tivity of the different soil types. The data do, however, show very 

 conclusively the influence of the character of the soil on tuber pro- 

 duction. 



TIME AND NUMBER OF IRRIGATIONS AS RELATED TO TUBER PRODUCTION. 



The material used for the study of the relation of irrigation methods 

 to tuber production consisted in 1917 of one row each of seven varie- 

 ties divided into four sections. The first received no irrigation. On 

 the second section irrigation was not begun until after tuber forma- 

 tion was well started. On the third and fourth sections the first appli- 

 cations of water were before tuber formation had started. On the 

 fourth section the number of irrigations was somewhat in excess of 

 what would be considered the optimum in commercial field practice. 

 At the time of harvest 30 hills were dug from each section of each 

 row (except in the fourth section of the Early Ohio, where disease re- 

 duced the number of healthy hills to 10), and the hills were weighed 

 and the tubers counted. 



In 1918 practically the same plan was followed, except that the 

 number of varieties was reduced to five, and each section of each 

 variety consisted of two full rows of approximately 200 hills each. 

 The effects of the early irrigations in this season were to some extent 

 counterbalanced by a relatively large rainfall between the periods of 

 germination and the beginning of tuber formation. 



