BackgroundAllelopathic functions of plant-released chemicals are often studied through growth bioassays assuming that these chemicals will directly impact plant growth. This overlooks the role of soil factors in mediating allelopathic activities of chemicals, particularly non-volatiles. Here we examined the allelopathic potential of 8-hydroxyquinoline (HQ), a chemical reported to be exuded from the roots of Centaurea diffusa.Methodology/Principal FindingsGrowth bioassays and HQ recovery experiments were performed in HQ-treated soils (non-sterile, sterile, organic matter-enriched and glucose-amended) and untreated control soil. Root growth of either Brassica campestris or Phalaris minor was not affected in HQ-treated non-sterile soil. Soil modifications (organic matter and glucose amendments) could not enhance the recovery of HQ in soil, which further supports the observation that HQ is not likely to be an allelopathic compound. Hydroxyquinoline-treated soil had lower values for the CO2 release compared to untreated non-sterile soil. Soil sterilization significantly influenced the organic matter content, PO4-P and total organic nitrogen levels.Conclusion/SignificanceHere, we concluded that evaluation of the effect of a chemical on plant growth is not enough in evaluating the ecological role of a chemical in plant-plant interactions. Interaction of the chemical with soil factors largely determines the impact of HQ on plant growth.

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Plastic mulching has significantly enhanced vegetable production worldwide since the 1950. It is used extensively due to its properties improved soil, plant growth, fruit quality properties and low cost. A field experiment was conducted to evaluate the influence of various color plastic mulches (white on black, silver on black and black on silver) and irrigation levels (60, 80 and 100 per cent ETc) on plant growth parameters and weed suppression in tomato (Solanum lycopersicum) cultivation at Madurai district, TamilNadu. The experiment was laid out according to factorial randomized block design with three replications. The results observed were soil temperature increased about 2-4 0 C under the colored plastic mulches as compared to control plot(Without mulch). Growth parameters of tomato such as plant height, number of branches per plant and leaf area index and total soluble solids of tomato were significantly influenced by colored plastic mulching and different irrigation levels. The maximum plant height (123.2 cm), maximum number of branches per plant (22.8), highest leaf area index (3.01) and highest chlorophyll (56.58) were recorded under white on black plastic mulch with 80 per cent Etc of drip irrigation when compared to other treatments.

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