Species and dynamics of floating weed seeds in paddy field
稻田水面漂浮的杂草种子种类及动态

In order to explore effective methods for weed control in paddy fields, we investigated the dynamics of weed seeds in Nanjing from June to November of 2005. A total of 24 weed species representing 15 families were found before seedling transplanting and at late growth stage of rice, while during irrigation stage, 26 species of 17 families were identified from floating weed seeds. The two stages shared 18 weed species, accounting for 56.25% of the total weeds. Most of them belonged to Gramineae, Polygonaceae, Ranunculaceae, Primulaceae, Cyperaceae, Compositae, and Pontederiaceae. There were more weed seeds and more species floating at the edge than in the middle of the paddy field. Some weed seeds could float longer, such as Beckmannia syzigachne, Lysimachia candida, Ranunculus chinensis, Rumex dentatus, Cnidium monnieri, and Alopecurus aequalis. Many floating weed seeds aggregated around rice stubble. In general, seeds began to sink abruptly after floating for two days, and most of them fell to the bottom after eight days. It is obvious that weeds in paddy fields can disperse through floating. Therefore, to filtrate water or clean floating weed seeds can help to reduce the seed weed amount so as to control weeds in paddy fields.