BIOCHEMICAL COMPOSITION OF COTTON LEAVES AND THEIR CHEMICAL DEFOLIATION AS AFFECTED BY ENVIRONMENT

Abstract

Induced defoliation of cotton became a necessity with the perfection of the mechanical cotton picker. Fortunately, a defoliant and some knowledge of its effectiveness was already available as a result of research to prevent boll rot in rank cotton (7). GULL (4) reported on the use of calcium cyanamide to remove the leaves from cotton plants to reduce the amount of leaf trash and stain in mechanically harvested cotton, and also, to reduce damage from certain insects and diseases that decrease production and lower the grade of lint cotton (5). The initial field trials for induced defoliation were extremely successful and a solution to the problem was thought to have been found. In subsequent years, however, it was soon found that effective defoliation was dependent upon the status of environmental factors (6); the physiological condition of the leaf, at the time the defoliant is applied, becomes the determining factor in causing abscission. Many field experiments have been conducted to determine the extent to which variation in different phases of the environment occasions alteration in the efficiency of chemical defoliation. From such studies it has been determined that vegetative-reproductive balance, moisture availability, and nutrient level each play a definite role in the efficiency of the defoliation process. EATON and RIGLER (2) report that a low concentration of carbohydrates in the cotton plant is responsible for much of the physiological shedding of small floral buds. Later, EATON and ERGLE (1) found that drought appeared to depress carbohydrate utilization to a greater extent than it did photosynthesis with the result that water deficit greatly increased the carbohydrate concentration within the cotton plant. The following experiment was designed to determine the influence that variation in boll load, moisture availability, and nutrient supply would have upon defoliation and to investigate the associated biochemical status of the leaves. The study was carried out under greenhouse conditions so that other variables, besides those specifically controlled, could also be held relatively uniform. The investigation was designed as a factorial experiment in order to allow for statistical evaluation of each variable and its influence upon the other variables in the study.