4 Journal oj Agricultural Research voi. ni, no. i 



WEIGHING AND WATERING 



The discarding of the overhead track necessitated the construction 

 of a movable support for -weighing the cans. The weighing support 

 used is shown in Plate II, figure 2. It was constructed of i-inch gal- 

 vanized-iron pipe and consisted of a crossbar which spanned the row and 

 which was supported at each end by two bent posts. These posts were 

 fitted with floor plates secured to two wooden skids, which slid along 

 the ground on either side of the row of cans. In the earlier weighings 

 the pots were suspended from a rope running through pulleys to a small 

 windlass located on one of the posts of the support (PI. II, fig. 2). The 

 windlass was later located directly beneath the crossbar and was operated 

 through a chain-and-sprocket drive. 



Each pot was provided with bale ears by which it could be suspended 

 directly from the balance by chains. When the plants were not suffi- 

 ciently high to come in contact with the weighing apparatus, pots could 

 be weighed at the rate of two a minute if two men handled the support and 

 a third recorded the weight. When 300 pots or more are to be weighed 

 three times a week, as was the case at Akron, rapidity in weighing be- 

 comes important. 



The initial and final weighings have been made with an accuracy of 

 one-fifth of a kilogram, either with a platform balance or a sensitive 

 spring balance calibrated and corrected for temperature. Intermediate 

 weighings have been made throughout with a spring balance calibrated 

 by means of a sealed check pot weighing 130 kg. 



The water in all cases has been added from calibrated 2-liter flasks 

 (Briggs and Shantz, 1913a, p. 11). The neck of each flask is cut so 

 as to deliver 2 liters of water when brimful. The flasks are filled by 

 submersion. In some of the later work a tank with a framework arranged 

 for keeping a number of flasks submerged has been used. No time is 

 thus lost in filling flasks or in adjusting the contents to a fiducial mark. 



SOIL FERTILIZER 



Surface soil from the experiment farm was used for filling the pots. 

 Since it is well known that the water requirement is increased by a 

 deficiency in the plant food supply (Briggs and Shantz, 1913b, pp. 31-56), 

 the same quantity of a complete soluble fertilizer was added to each pot 

 at each station at intervals during the growth of the crop. The fertilizer 

 in 1 91 2 was applied at the rate of 50 p. p. m. of PO4, 100 p. p. m. of NO3, 

 and 65 p. p. m. of K, all based on an assumed dry soil mass of 100 kg. 

 per pot.' The phosphoric acid was applied as sodium phosphate; the 

 nitrogen and potash as potassium nitrate. This amount of fertilizer was 

 divided into four equal portions and applied at intervals during the 

 active growth of the crops, the first application being made soon after 



* Approximately one-half of this quantity was used in 1913 and was applied as in 1912. 



