4 BULLETIN 1018, U. S. DEPARTMENT OF AGRICULTURE. 



Beginning on April 22, soil samples for moisture determinations 

 were taken each week in foot sections to a depth of 6 feet. 



Immediately after thinning, 20 normal plants were selected in each 

 plat and designated as observation plants. To minimize the error 

 which might result from soil variations, 5 plants were selected 29 

 feet apart in each alternate row, excluding the outside rows, thus 

 locating the 20 plants on four alternate inside rows, so that each 

 represented an area of approximately one two-hundredths of an acre. 



Measurements of the growth of the main stem of these plants were 

 recorded each week on the same day that moisture samples were 

 taken. This was accomplished by measuring from an india-ink 

 mark near the ground to the tip of the terminal bud. In planning 

 the experiments it was decided that a detailed study of a few indi- 

 vidual plants selected in the above-described manner and produced 

 under different conditions of soil moisture and available food supply 

 would be of greater service in providing a better knowledge of the 

 water requirements of the crop than a cursory inspection of a large 

 number of plants studied collectively. 



Beginning with the appearance of the initial flower about June 

 30, the flowers on each of the selected record plants were marked with 

 the date of opening, in order to determine the length of the develop- 

 ment period of the boll and to obtain information in regard to 

 shedding. 



ADAPTATION AND LENGTH OF THE DEVELOPMENT PERIOD. 



The Pima variety, which is the only kind of cotton now grown in 

 the Salt Biver Valley, seems in many ways admirably adapted to the 

 climate of that district. Thus far in the history of the industry there 

 have been no very destructive insect pests or diseases to affect the 

 yield on a large scale, and storm damages have been infrequent. 

 Yields of a bale and more per acre have not been uncommon, yet the 

 average yield for the whole producing area for several years has 

 been less than one-half bale per acre. Some of the growers would 

 attribute this low average to the comparatively long development 

 period required by the Pima Egyptian crop. While other factors, 

 such as the location of a part of the crop on poorly adapted soils 

 and in the hands of inexperienced growers, undoubtedly are largely 

 responsible for the low average jdelds, yet the length of season re- 

 quired is of no little importance in the greater part of the Salt Biver 

 Valley, where comparatively early frosts have been responsible for 

 serious damage to the late crop of bolls. This has been the case 

 especially where heavy soils or delayed preparation made planting 

 impossible before the middle of April. It has been estimated by some 

 of the growers that the heavy frost of November 1, 1919, was re- 

 sponsible for destroying from 15 to 20 per cent of the bolls on about 



