Changes in the weed seed bank over 9 consecutive years of rice–duck farming

Rice–duck farming (RDF), a form of organic farming, has been widely adopted in rice production in East Asia. In RDF, it is believed that ducks can control weeds effectively. Since the weed seed bank determines the weed community in the following crop, a better understanding of the seed bank could provide useful insights into the long-term effects of RDF adopted for weed control. Nine consecutive years' field experiments were conducted to study the characteristics of the weed seed bank under RDF and evaluate the weed control effect of RDF. After 9 years under RDF, the number of weed species in the weed seed bank declined from 38 to 21 and the density of both the weed seed bank and the above-ground weed decreased by more than 90%. RDF resulted in a more uniform vertical distribution of the weed seed bank both quantitatively and qualitatively. The ecological indices point to a gradual change towards fewer species, lower density, and lower diversity following continued RDF. The dominant species in the weed seed bank shifted from Lindernia procumbens, Mazus japonicus, Cardamine hirsuta, and Alopecurus aequalis at the beginning of this experiment in 1999 to A. aequalis, Rotala indica, M. japonicus, and Cyperus difformis in 2008. The results provide concrete evidence for the efficacy of RDF in depleting the weed seed bank and as a weed management approach without any herbicides.

► Nine years of rice–duck farming was conducted to understand its weed control effects.
► Weed density and species reduced greatly in seed bank and above-ground weed community.
► The weed seed bank changed to lower diversity.
► Vertical distribution of the weed seed bank became uniform more and more.
► Rice–duck farming can be used as an effective weed control method in organic farming.