

WATER-STRESS BEHAVIOR OF PIMA COTTON. 21 



the moisture content of soil samples taken in juxtaposition to the 

 plants 24 hours after the application of water showed no increase 

 above the fourth-foot layer but marked increase in the fifth-foot 

 layers. The plants grown under this method of irrigation in 1919 

 behaved in a very satisfactory manner and did not show the marked 

 slowing up of the growth and flowering rates late in the season 

 exhibited by the plants on plats 1 and 2. In 1920 this method of 

 irrigation on heavy soil was adopted commercially by Mr. Parker 

 and proved very satisfactory. The plants which were irrigated at 

 approximately 10-day intervals during the principal fruiting season 

 fruited very heavily, with little loss from shedding, and the total 

 yield per acre was considerably greater than had been obtained on 

 the same soil in several years previously. The encouraging results 

 obtained in these tests with a double-row method of cotton culture 

 and reports of frequent successes in tests with a somewhat similar 

 method at the Bard station point to the need of further experiments 

 along this line. There seem to be possibilities of solving several 

 important problems of cotton culture under irrigation by perfecting 

 some such method. 



CONCLUSIONS. 



This bulletin reports the results of an investigation of the behavior 

 of Pima cotton when grown under different conditions of soil mois- 

 ture and available plant food in the Salt River Valley of Arizona 

 in 1919. 



The normal growing season in the Salt River Valley, while usually 

 ample for substantial yields, is none too long for the complete de- 

 velopment of the Pima cotton plant, and precaution on the part of 

 growers is necessary in selecting a proper date for planting and to 

 keep the plants in full activity during the limited time available for 

 boll production. The occurrence in some years of heavy frosts about 

 November 1 has occasioned considerable damage to the late crop of 

 bolls. 



The mean period of maturation for over 3,000 bolls of Pima cotton 

 was 68 days. 



In Arizona early bolls mature within a much shorter period than 

 later bolls. The mean difference in time required for maturation 

 between bolls developed from flowers blooming in July and those 

 blooming in September was 27 days. 



Plants which had produced the greatest quantity of vegetative 

 growth appeared to suffer most frequently from " water stress," re- 

 maining longer in a wilted condition between irrigations and show- 

 ing an earlier recurrence of wilting after irrigation. 



The fact that there was no appreciable difference in size or distri- 

 bution between the roots of large plants and small plants seems to 



