Abstract
Intensive usage of herbicides can result in the serious negative impacts on environment. Allelopathy by reducing seed germination and early seedling growth can play a fundamental role in suppressing weeds in crop fields. The effectiveness of allelochemicals is governed by different factors such as soil nutrient status, pH and microorganisms. Outdoor pot experiments were conducted at the Faculty of Agriculture and Natural Resources of Razi University, Kermanshah, Iran, in 2013, to evaluate the effects of different levels of N fertilizer (0, 150, 300 kg ha<sup>-1</sup>) on the suppressing effects of alfalfa (<em>Medicago sativa</em> L.), sorghum (<em>Sorghum bicolor</em> L.), and tobacco (<em>Nicotiana tabacum</em> L.) plant materials on emergence and growth parameters of some weed species including Johnson grass (<em>Sorghum halepense </em>(L.) Pers.), barnyard grass (<em>Echinochloa crus-galli</em> (L.) Beauv.) and redroot pigweed (<em>Amaranthus retroflexus</em> L.). Results indicated that adding plant materials of tobacco, sorghum, and alfalfa substantially reduced seed germination and early growth of the tested weeds. However, the weed species responded differently to the presence of the allelopathic plant materials. The use of N fertilizer had significant effects on the inhibitory potentials of the allelopathic plants. However, we didn't find consistent trends regarding the responses of the allelopathic crops to elevated N fertilizer levels in related to the traits under study.
Highlights
Based on the oldest definition by Molisch (1937), the adverse effect of one plant species on neighboring plants via releasing of toxic chemicals is called as allelopathy
The results showed that alfalfa had the greatest reducing effect on barnyard grass seedling emergence under all three nitrogen levels with a positive response to increasing nitrogen fertilizer (Table 1), as the lowest seedling emergence caused by alfalfa occurred at the highest N level
Root dry mass responded positively to the increasing N level under tobacco and sorghum treatments, this trait was not significantly influenced by N application when soil was treated by alfalfa plant material (Table 1)
Summary
Based on the oldest definition by Molisch (1937), the adverse effect of one plant species on neighboring plants via releasing of toxic chemicals is called as allelopathy. Several plant species have shown allelopathic capability (Macias et al, 2004). Alfalfa plant tissues and their aqueous extracts can inhibit the germination and seedling growth of a number weed species (Singh et al, 2003). Florentine et al (2005) reported that the aqueous extract of tobacco shoots have inhibitory effects on growth and germination of some crops. According to Singh et al (2003) all parts of sorghum release phytoinhibitors reducing the growth of grass and broadleaf weed species. By integrating of allelopathic plants to a weed management program, the need for herbicide to control weeds would diminish substantially (Dilipkumar et al, 2012)
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