Occurrence and biological characteristics of Ammannia arenaria
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.
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