Boll Retention and Boll Size among Intrasympodial Fruiting Sites in Cotton

摘要

Competition among cotton (Gossypium hirsutum L.) bolls for assimilates may affect boll retention and size, making it an important factor affecting productivity. A 4-yr field study was conducted on Commerce silt loam to evaluate relationships among fruiting sites (FS) on sympodial branches of cotton receiving preplant fertilizer N rates of 0, 28, 56, 84, 112, 140, or 168 kg haa?’1 or a preplant + sidedress application of 56 + 56 kg haa?’1 each year. For each FS on each sympodium, there were four possible competition levels based on boll retention or abscission at FS 1, 2, and 3. Competition levels were determined by natural retention or abscission of fruit. Boll retention and weight were influenced by competition level, year, sympodia, FS location on the sympodia and by N rate. Competition effects on boll retention were affected by N rate but not by sympodia. Conversely, competition effects on boll weight were not affected by N rate but were affected by sympodia. Boll weight at FS 1 increased when bolls were retained at FS 2 and 3. Retention of a boll at FS 1 increased boll retention at FS 2 but decreased boll weight at FS 2. In contrast, boll weight at FS 2 increased when bolls were retained at FS 3, or at FS 1 and 3. Fertilizer N increased boll weight at FS 2, except when a competing boll was present at FS 1. Apparent increased competition among FS on a sympodium had favorable effects on boll retention and on boll weight except for FS 2 when FS 1 retained a boll and FS 3 did not retain a boll.