Relationship of Seasonal Trends in Carbohydrate and Nitrogen Levels and Effects of Girdling and Spraying with Sucrose and Urea to the Nutritional Interpretation of Boll Shedding in Cotton

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Abstract
Spraying the upper leaf surface of plants daily through the fruiting period with 20% sucrose, 1% N (urea) and the 2 in combination failed to improve growth and resulted in large significant decreases in the number of bolls that were set. Flowering rates were not affected. Sucrose was not accumulated. N was absorbed and resulted in much lower sugar and starch concns. in all tissues. The urea when used alone burned the margins of the leaves severely but not when combined with sucrose; in this case it greatly reduced N accumulation. In an expt. in August when control plants were shedding over half of their bolls, girdling, 2% urea spray (6 times) and the 2 together caused large increases in boll shedding. The girdling increased carbohydrate levels, and the urea spray increased N and reduced carbohydrate; the 2 in combination increased both. In mid-August the concns. of sugar, starch and N in stems and 13 day old bolls were found to be similar in an early planting that was shedding most of its bolls and in a late planting that was retaining its bolls. It is concluded that the nutritional theory of boll shedding is poorly supported at least as regards carbohydrate and N relations. Even though the relative number of bolls carried by a cotton plant, or the percentage of bolls shed, is apparently not influenced by the level of carbohydrate or N supply, the absolute number it may develop is so affected. Within vars. and environments, the number of bolls per 100 g. of fresh stems and leaves remains rather constant even though nutritional factors may cause marked differences in plant growth.