Ammannia arenaria H. B. K. Is a new dominant weed in paddy fields in Shanghai. In order to understand its occurrence, we carried out investigation and fixed-point observation in fields, and studied the biological characteristics in the laboratory. The results showed that A. Arenaria could emerge in the whole growing period of rice, and there were two peaks of occurrence in the 1st and 3rd week after rice seeding. The population of A. Arenaria reached its peak 45 days after rice seeding, and then dropped. The optimum temperature for seedling emergence of A. Arenaria was 23-27 ℃. As an aquatic weed, it was adapted to the humidity and saturated soil condition, and showed higher emergence rate when water content ranged from 40% to 60%. The seeds of A. Arenaria could normally germinate 10 cm under water, but its ability of emergence was very weak. Soil cover of 0.5 cm depth could effectively inhibit seedling emergence.%为明确上海地区稻田新优势杂草耳叶水苋的发生规律,对上海地区稻田中耳叶水苋的发生情况进行了田间调查和定点观察,并在室内研究了其生物学特性.结果表明,耳叶水苋发生周期长,有两个明显的发生高峰,分别为水稻播种后第1周和第3周.水稻播种后45 d,耳叶水苋种群数量达到最大,随后,种群数量逐渐下降.耳叶水苋的种子在23～27℃条件下发芽最好.作为一种水生杂草,其种子在土壤含水量40％～60％的湿润或饱和状态下,发芽率较高,且耳叶水苋的种子对水层具有较好的适应能力,即使处于10 cm水层下也可以正常萌发.耳叶水苋种子极小,其顶土能力较差,覆盖0.5 cm土层能有效抑制其出苗.
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