270 Bulletin 90 



tively deep and reasonably close to the plant. Late cultivations must 

 be shallow in order to avoid cutting and breaking numerous cotton 

 roots. 



IRRIGATION OF COTTON 



The proper irrigation of cotton is the most important single item 

 in the profitable growing of the crop. Even though all other condi- 

 tions are right, if the irrigation is wrong the yields will not be satis- 

 factory. Over-irrigation stimulates plant growth, and to a certain ex- 

 tent prevents the forming of cotton squares and the setting of bolls; 

 while light irrigation encourages the setting of fruit and the dwarfing 

 of the plant, which are highly desirable especially in the earlier stages 

 of growth of American Egyptian cotton. However, this dwarfing of 

 the plant is neither necessary nor desirable on light desert soils defi- 

 cient in both nitrogen and humus. When a plentiful supply of water 

 is suddenly applied, following a period when the plant has been suf- 

 fering for water, it will cause a quick stimulation of growth and the 

 plant will shed or drop much of the young fruit already set. It is 

 best to withhold irrigation after planting as long as possible and still 

 keep the plants in a growing condition. Cotton will not be injured by 

 wilting slightly in the middle of the day, provided it fully recovers its 

 fresh appearance by late afternoon or early evening, and provided there 

 is enough moisture deep in the soil to encourage deep root penetration. 

 As long as there is sufficient moisture in the ground to permit trans- 

 piration to maintain the leaves in a cool condition during the heat of 

 the day, the plant is not suffering, but when the leaf feels warm to the 

 hand irrigation must be immediately supplied. After cotton begins to 

 bloom the moisture supply should be kept as uniform as possible. 

 Cotton should be kept growing steadily, but excessive growth should 

 be prevented. If examination during the blooming stages shows that 

 the vegetative growth has practically stopped and the cotton is bloom- 

 ing to the top of the plant, water has been withheld too long. In other 

 words, the terminal bud should be kept growing slightly in the lead of 

 the flowers on the fruiting branches. 



Prior to fruiting the desirable method is to give as little water as 

 possible, forcing roots to penetrate deeply for soil moisture stored prior 

 to planting. The system changes after the fruiting begins, and the pur- 

 pose then is to maintain a thrifty and uniform though not rank growth. 



PICKING 



In Arizona, cotton picking is usually begun during the last half of 

 September. It does not pay to begin picking until sufficient cotton 



