Benzoic (BEN) and cinnamic (CIN) acids are commonly found in soils and are considered as strong allelochemicals. Published information suggest that BEN and CIN and other phenolic acids decrease plant growth in part by suppressing nutrient absorption. However, studies on the mechanism of action were not conclusive. We examined the effects of BEN and CIN on the cell plasma membrane in intact soybean (Glycine max L. cv. Maple Bell) seedlings. Treating intact root systems with BEN or CIN rapidly increased electrolyte leakage and ultraviolet absorption of materials into the surrounding solution. After 12 hr of treatment, BEN and CIN lowered the extracellular sulfhydryl group content in roots. The two allelochemicals induced lipid peroxidation, which resulted from free radical formation in plasma membranes, inhibition of catalase and peroxidase activities, and sulfhydryl group depletion. Oxidation or cross-linking of plasma membrane sulfhydryl groups is the first mode of action of both compounds. The BEN- and CIN-induced decrease in soybean nutrient absorption may be a consequence of damage to cell membrane integrity caused by a decrease in sulfhydryl groups followed by lipid peroxidation.

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, J. 1998. Effects of de-inking paper sludges on soil properties and crop yields. Can. J. Soil Sci. 78: 689-697. The paper mills in Quebec produce approximately 330 000 Mg of raw de-inking paper sludges (RDS) per year. These residues are rich in cellulose and lignin and may be used as soil conditioner. The effects of RDS on soil chemical properties, barley (Hordeum vulgare L. 'Chapais') growth, nutrient uptake and yields, and their residual effect on a subsequent strawberry (Fragaria × ananassa Duch. 'Kent') crop were investigated on a Tilly silt loam (Gleyed Humo-Ferric Podzol) from 1994 to 1996. Four rates of RDS (0, 15, 30 and 45 Mg ha -1 ) on a wet-weight basis were combined with four rates of supplemental N-mineral fertilizer (0, 45, 90 and 135 kg ha -1 ) as NH 4 NO 3 . The soluble inorganic N content of soil sampled 30 d after treatment application was significantly lower in plots treated with 45 Mg RDS ha -1 at all N rates. However, soluble inorganic N concentrations increased significantly with RDS rate to 20-cm depth in June 1995. The RDS application increased soil water content and Mehlich-3-extractable P, K, and Ca in the first year. Barley yields were reduced by 50% when 45 Mg RDS ha -1 was applied without supplemental N-mineral fertilizer. The amount of N-mineral fertilizer needed to overcome N immobilization resulting from RDS increased with RDS rates. Strawberry yields were not significantly affected by residual RDS or N-mineral fertilizer. Changes in plant tissue metal contents were not significant. The results of this study indicate that RDS application has a positive short-term effect on soil water, P and K availability but reduces plant-available soil N in the growing season after spring application. The RDS may be used effectively as soil amendment if the crop receives adequate supplemental N-mineral fertilizer. Par contre, l'azote minéral dans la couche de 0-20 cm de sol en juin 1995 augmentait avec la dose de BDD. Les BDD ont entraîné une augmentation de la teneur en eau et en carbone du sol lors de l'année d'application. De plus, les teneurs en P, K et Ca extractibles par la solution Mehlich-3 ont augmenté suite à l'apport de BDD. Un apport de BDD à raison de 45 Mg ha -1 a diminué le rendement d'orge de 50%. Un apport supplémentaire de N minéral a résulté en une augmentation de rendement d'orge. Les BDD n'ont pas eu d'effet résiduel sur la production de fraises. Aucune augmentation de la teneur en métaux lourds n'a été détectée dans les tissus d'orge ou de fraises. Ces résidus peuvent être considérés comme un amendement organique. Toutefois, un apport supplémen-taire d'azote minéral à la culture doit être envisagé pour éviter les problèmes de carence en N.

Competitive cereal cultivars are less susceptible than others to weed interference. Their characterization may provide selection criteria that can be used as guidelines to develop new, even more competitive cultivars. Root exudates are a potential means by which competitive cultivars reduce weed growth. The objectives of this study were to evaluate the effect of cereal root exudates onBrassica kaber(DC.) L. C. Wheeler growth, to isolate and characterize the allelochemical compounds released by spring cereal cultivars, and to determine if a relation exists between these allelochemicals and cultivar competitiveness. Highly competitive (HC) and lesser competitive (LC) cultivars of four crop kinds (Triticum aestivumL. [wheat],Avena sativaL. [wild oat], two- and six-rowedHordeum vulgareL. [barley]) were selected based on previous work. Exudates from undisturbed root systems ofB. kaberand cereals were collected and used in a bioassay test withB. kaber.Root exudates were analyzed for 16 common phenolic compounds using high-performance liquid chromatography (HPLC). Bioassays indicated that cereal exudates had no negative effect onB. kabergermination, but all concentrations of cereal root exudates inhibitedB. kaberroot and hypocotyl growth. As cereal root exudate concentration increased,B. kabergrowth decreased. For each crop kind,B. kabergrowth inhibition was greater with HC cultivars than with LC cultivars. The root exudates of all crop kinds and cultivars contained benzoic, caffeic, ferulic,o-coumaric, and vanillic acids as well as scopoletin. Para-hydroxybenzoic acid was found in exudates fromT. aestivum, A. sativa, and two-rowedH. vulgarecultivars. Para-coumaric acid was not identified in root exudates from LCH. vulgarecultivars. Gentisic acid was produced byA. sativaandH. vulgare.Vanillic ando-coumaric acids along with scopoletin may be responsible for the allelopathic effects ofH. vulgare, T. aestivum, andA. sativacultivars. These three compounds may be useful as possible indicators of allelopathic potential of genotypes under development and thus considered for use in breeding programs.

Organic acids are major water-soluble allelochemicals found in soil infested with quackgrass and are involved in several processes that are important in plant growth and development. This study was carried out to gain more information on the effects of benzoic acid (BEN) andtrans-cinnamic acid (CIN) on growth, mineral composition, and chlorophyll content of soybean [Glycine max (L.) Merr. cv. Maple Bell] grown in nutrient solution. The two allelochemicals reduced root and shoot dry biomass of soybean. Treated plants had fewer lateral roots and tended to grow more horizontally compared to the untreated plants. Lateral roots were stunted and less flexible. The amounts of P, K, Mg, Mn, Cl(-), and SO 4 (2-) were lower, and Zn and Fe contents were higher in roots of plants grown with BEN or CIN as compared to untreated plants. Shoots of plants grown with the allelochemical showed greater accumulation of Ca, Mg, and Zn, whereas P and Fe contents were reduced. The BEN and CIN also caused reductions in leaf chlorophyll content. The BEN and CIN may be responsible for negative allelopathic effects of quackgrass on soybean by inhibiting root growth, by altering ion uptake and transport, and by reducing chlorophyll content.