WEED INTERFERENCE IN COTTON PLANTS GROWN WITH REDUCED SPACING IN THE SECOND HARVEST SEASON

ABSTRACT Changes in row spacing may result in changes in crop and weed behavior and crop-weed competition. A study was performed to determine the periods of weed presence and weed control in cotton sown with 0.76 m spacing between planting rows. Cotton cultivar FM 993 was sown on 01/08/2010 with the aim of reaching a density of 190,000 seeds ha-1. Treatments with either weed presence or weed control during the first 0, 5, 10, 15, 22, 29, 36, 43, 50, 57, 64, 71, and 190 days of cultivation were established to determine the period prior to weed interference (PPI), total period of interference prevention (TPIP) and critical period of weed control (CPWC). The weed species with high relative importance were Amaranthus retroflexus, Bidens pilosa, Eleusine indica, Digitaria horizontalis, Alternanthera tenella, and Commelina benghalensis. Considering a maximum yield loss of 5%, the PPI was established 11 days after cotton emergence (DAE), the TPWC at 46 DAE, and the CPWC between 11 and 46 DAE, for a total duration of 35 days. Considering a maximum acceptable yield loss equal to the standard deviation for the weed-free treatment, the PPI was established at 6 DAE, the TPWC at 55 DAE, and the CPWC between 6 and 55 DAE for a total duration of 49 days

摘要
行距变化可引发作物与杂草的生长特性及二者间竞争关系的改变。本研究针对种植行距为0.76 m的棉田，旨在明确杂草存在时段与杂草防控关键时期。供试棉花品种为FM 993，于2010年1月8日播种，目标种植密度为190000粒/公顷。本研究设置了如下处理组：在棉花生育前期的0、5、10、15、22、29、36、43、50、57、64、71及190天内，分别维持杂草存在或实施杂草防控，以此测定杂草干扰始前期（Period Prior to Weed Interference, PPI）、完全干扰防控期（Total Period of Interference Prevention, TPIP）以及杂草临界防控期（Critical Period of Weed Control, CPWC）。相对重要性较高的杂草物种包括反枝苋（Amaranthus retroflexus）、三叶鬼针草（Bidens pilosa）、牛筋草（Eleusine indica）、止血马唐（Digitaria horizontalis）、细叶莲子草（Alternanthera tenella）以及孟加拉鸭跖草（Commelina benghalensis）。当设定最大允许产量损失为5%时，PPI为棉花出苗后11天（Days After Emergence, DAE），杂草防控总时长（Total Period of Weed Control, TPWC）为46 DAE，杂草临界防控期为11~46 DAE，总持续时长为35天。当以无杂草处理组的标准差作为最大可接受产量损失阈值时，PPI为6 DAE，TPWC为55 DAE，杂草临界防控期为6~55 DAE，总持续时长为49天。