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Use of phytotoxic rice crop residues for weed management
Pheng, Sophea,Olofsdotter, Maria,Jahn, Gary,Adkins, Steve The Korean Society of Weed Science and The Turfgra 2010 Weed Biology and Management Vol.10 No.3
There is a general perception among Cambodian rice (Oryza sativa) farmers that, after harvesting, rice crop residues that are incorporated into the field benefit the growth of the subsequent rice crop. However, the effect of this action upon weed establishment and growth has not yet been considered. A series of pot and field trials were conducted to determine whether such action could inhibit weed establishment and/or growth. The pot studies first evaluated the response of the test plant (rice line ST-3) and three weed species, barnyardgrass (Echinochloa crus-galli), small umbrella sedge (Cyperus difformis), and water primrose (Ludwigia octovalves), to the residue of 16 rice lines and the field trials were later conducted to evaluate the response of the same test plants to the residue of seven putatively allelopathic rice lines and one non-allelopathic rice line. The residue of all the studied rice lines, depending on how long they had been incorporated into the soil, reduced the establishment and growth of all three weed species, as well as the rice crop. However, if the residue's incorporation was delayed by 2 weeks or only a proportion of the residue was incorporated, the rice crop could withstand the growth-inhibiting effect, while the inhibition of the establishment and growth of the three weed species was retained. These responses of rice and the weeds to rice crop residues might provide a basis for a weed management strategy, particularly in the resource-poor rice-production systems of Cambodia.
Evaluation of rice allelopathy in hydroponics
KIM, S Y,MADRID, A V,PARK, S T,YANG, S J,OLOFSDOTTER, M Blackwell Science Ltd 2005 Weed research Vol.45 No.1
<P>Summary</P><P>The inhibitory activity of water extracts from the shoots and roots of three rice cultivars, Taichung native 1 (TN1) and IAC165 (both allelopathic rice) and AUS196 (non-allelopathic rice), grown in hydroponics was evaluated. The release of germination inhibitors by allelopathic rice plants into hydroponic solution was also determined with freshly collected solution and XAD-4 resin desorbate. The degree of the inhibition was quantified in terms of root growth in <I>Echinochloa colona</I>, <I>Echinochloa crus-galli</I>, <I>Echinochloa crus-galli</I> var. <I>oryzicola</I>, <I>Triantema portulacastrum</I> and <I>Lactuca sativa</I>. The allelopathic activity of rice was species specific, and depended on source and concentration. Root length of all test species was inhibited by the different concentrations of shoot extract of allelopathic and non-allelopathic rice. However, of the three cultivars, TN1 showed higher inhibition than IAC165 and AUS196 in all test species. Water extracts of shoots and roots significantly inhibited root growth in <I>E. crus-galli</I> but the shoot extract gave a greater inhibitory effect on <I>E. crus-galli</I> than the root extract. Root exudate of TN1 inhibited root elongation of <I>E. crus-galli</I> from 2 weeks after transplanting (WAT) and the inhibition continued for 4 WAT. The results confirmed the previous finding of a laboratory bioassay that the TN1 had allelopathic activity and produced allelochemicals that inhibit growth of some weed species.</P>