UNITED STATES DEPARTMENT OF AGRICULTURE 



H BULLETIN No. 1018 %mB* 



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Contribution from the Bureau of Plant Industry 

 WM. A. TAYLOR, Chief 



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Washington, D. C. 



PROFESSIONAL PAPER 



March 15, 1922 



WATER-STRESS BEHAVIOR OF 



ARIZONA. 



PIMA COTTON IN 



By C. J. King, Assistant, Office of Biophysical Investigations. 



CONTENTS. 



Scope of the investigations 



Location and plan of the experi- 

 ments 



Adaptation and length of the de- 

 velopment period 



AVater-stress behavior 



Water relations and the shedding of 

 immature bolls 



Page. 

 1 



11 



Page. 



Shedding studies under Arizona con- 

 ditions 12 



The period between flowering and 



shedding 15 



Variations in periodicity of develop- 

 ment 15 



Conclusions 21 



Literature cited 23 



SCOPE OF THE INVESTIGATIONS. 



American Egyptian long-staple cotton, which was first grown com- 

 mercially in 1912, is now one of the principal crops of Arizona and 

 portions of California. In 1920 approximately 250,000 acres were 

 planted to this crop in the States mentioned. The acreage planted 

 to the Pima variety of American Egyptian cotton in the Salt River 

 Valley far exceeded that of any other crop in 1920. 



An investigation of the practicability of using soil-moisture deter- 

 minations as an index of the water requirement for growing Pima 

 cotton was begun in 1918 and continued through the year 1919, in the 

 belief that definite information would be of value in determining the 

 best methods of irrigation, which is a very important feature in the 

 production of the crop. The plan in 1919 was to apply water so as 

 to keep different amounts of moisture available at various depths 

 of soil and to study the behavior of the plants in response to the 

 different proportions of soil moisture, in order to learn the quantity 

 of water that would give the best development of the crop. This 

 bulletin relates to the data obtained in 1919, after the experience of 

 the previous year had demonstrated that it was possible to control 



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