<br><div><section class="_135editor" data-role="paragraph" style="font-size: medium; max-inline-size: 100%; margin: 0px; padding: 0px; border: 0px none; z-index: 0; overflow-wrap: break-word !important; outline: none 0px !important;"><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; line-height: 1.75em; overflow-wrap: break-word !important; outline: none 0px !important;"><span style="max-inline-size: 100%; margin: 0px; padding: 0px; cursor: text; font-size: 15px; overflow-wrap: break-word !important; outline: none 0px !important;">　　黄河流域适期春播的棉花一般在４月底５月初出苗，到６月上中旬开始现蕾，大约历时４５天。从出苗到２～３片真叶展平（顶端开始分化第一个花芽）为幼苗期；之后到现蕾为孕蕾期。苗期以营养生长为主（长根、茎、叶），并开始花芽分化。主要生育特点为：①长根是棉花的生长中心，地下根系的生长比地上部快。从子叶到三叶期，主根每天向下伸长１.５～２厘米，出现第一片真叶时，主根长度等于株高的２.６～２.８倍，分生侧根数可达８０～９０条；现蕾时，主根下扎深度可达７０～８０厘米，长度为株高的４～５倍。</span></p><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; overflow-wrap: break-word !important; outline: none 0px !important;"><br style="max-inline-size: 100%; margin: 0px; padding: 0px; overflow-wrap: break-word !important; outline: none 0px !important;"></p><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; line-height: 1.75em; overflow-wrap: break-word !important; outline: none 0px !important;"><span style="max-inline-size: 100%; margin: 0px; padding: 0px; cursor: text; font-size: 15px; overflow-wrap: break-word !important; outline: none 0px !important;">　　②由于苗期营养体小，对养分的吸收量也少。吸收积累的氮素占一生吸收总量的４.５％～６.８％，磷素占３％～５.５％，钾素占３.7％～５％。③氮素代谢旺盛。棉花一生中的含氮水平以这个时期为最高，糖类绝大部分用于合成蛋白质，形成叶与茎的结构物质，部分氮则运往茎内以可溶性盐贮藏起来。氮素在叶内的比例比在茎内大。此时营养物质主要用于叶的生长，茎部的可溶性氮含量较高，主要起贮藏作用。④对温度和光照敏感。晴天越多，温度越高，苗期越短，苗病越轻，棉苗越旺。</span></p><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; overflow-wrap: break-word !important; outline: none 0px !important;"><br style="max-inline-size: 100%; margin: 0px; padding: 0px; overflow-wrap: break-word !important; outline: none 0px !important;"></p><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; line-height: 1.75em; overflow-wrap: break-word !important; outline: none 0px !important;"><span style="max-inline-size: 100%; margin: 0px; padding: 0px; cursor: text; font-size: 15px; overflow-wrap: break-word !important; outline: none 0px !important;">　　高产棉花要求苗期的长势长相是，植株敦实，宽大于高；茎粗节密，红绿各半；叶片平展，大小适中，叶色青绿；顶心凹陷；苗期平均主茎日增长量０.３～０.５厘米，现蕾时株高１２～１５厘米，即“二叶平，四叶横，六叶亭”的壮苗长相。</span></p><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; overflow-wrap: break-word !important; outline: none 0px !important;"><br style="max-inline-size: 100%; margin: 0px; padding: 0px; overflow-wrap: break-word !important; outline: none 0px !important;"></p></section><section class="_135editor" data-role="paragraph" id="autoparagraph" style="font-size: medium; max-inline-size: 100%; margin: 0px; padding: 0px; border: 0px none; z-index: 0; overflow-wrap: break-word !important; outline: none 0px !important;"><p style="max-inline-size: 100%; margin-bottom: 0px; clear: both; min-height: 1em; cursor: text; overflow-wrap: break-word !important; outline: none 0px !important;"><br style="max-inline-size: 100%; margin: 0px; padding: 0px; font-family: 微软雅黑, &quot;Microsoft YaHei&quot;, sans-serif; font-size: 17px; caret-color: rgb(255, 0, 0); overflow-wrap: break-word !important; outline: none 0px !important;"></p></section></div>