Allelopathy weed suppression

Providing weed suppression through the use of allelopathic cover crops is an important method of weed control in organic farming and it is one of the best possibilities of allelopathy application (Sullivan 2003a). Besides, growing of cover... 

Fisk JW, Hesterman OB, Shrestha A, Kells JJ, Harwood RR, Squire JM, Sheaffer CC (2001) Weed suppression by annual legume cover crops in no-tillage com. Agron J 93 319-325 Fujii Y (2003) Allelopathy in the natural and agricultural ecosystems and isolation of potent allelochemicals from velvet bean (Mucuna pruriens) and hairy vetch (Vicia villosa). Biol Sd Space 17 6-13... 

An obvious place for intensive work on allelopathy is in the weed science area. Here, plant interference is either our problem or our opportunity. We should be clever enough to exploit allelopathy as a weed-suppression strategy. This could be accomplished with crops that release allelochemicals through exudation or by crop residues placed into sequential cropping systems. My research team and others have already developed some promising leads in this area. 

Additional benefits derived from cover cropping include weed and disease suppression. Approaches for managing weeds are discussed below however, the main mechanism of weed suppression by cover crops appears to be resource competition, rather than factors such as allelopathy (Bond and Grundy 2001). The different occurrence of the fungal pathogen... 

The presence of crop residues has been reported to both increase (5, 6) and decrease crop yields ( 7) and not tilling to increase certain difficult to control weeds (8). However, other reports indicate that the presence of certain mulches can reduce the biomass of certain weeds (9-15) and allow for higher crop yields ( 5, 6). Thus, under certain conditions, mulches can suppress certain weed species, but determining the reason(s) presents many logistical problems, especially under field conditions. To determine the cause(s), the physical and chemical (i.e., allelopathy) effects of the mulch and the role of soil disturbance (or the lack of, as would be the case in a no-till system) must be separated. 

Intercropping may facilitate weed control if intercrops are more weed competitive than sole crops or are able to suppress weed growth through allelopathy (the weed species is more susceptible to such phytotoxin than crops). If intercrops do not suppress weeds more than sole crops, they should provide yield advantages due to better utilization of resources or by converting resources than in case of sole crops (Liebman and Dyck 1993). 

Posler GL, Lenssen AW, Fine GL (1993) Forage yield, quality, compatibility, and persistence of warm-season grass-legume mixtures. Agron 1 85 554—560 Putnam AR, Duke WB (1974) Biological suppression of weeds - evidence for allelopathy in accessions of cucumber. Science 185 370-372... 

Several phenolic acids and many nonspecific allelopathic conditions have been shown to alter the mineral content of plants, and certainly phenolic allelochemicals may perturb cellular functions in a number of ways that are of importance to plant nutrition (34,35). However, raising fertility does not always suppress allelopathic inhibition, and the interrelationships between these two factors are still not clear. Bhowmik and Doll (36) showed that allelopathic inhibition of corn and soybeans by residues of five annual weeds was not alleviated by supplemental nitrogen or phosphorus. Similarly, an increase in fertilizer did not overcome inhibition of corn by quackgrass or circumvent the autotoxicity of berseem clover Trifolivm alexandrium L.) (37,38). Even when raising nutrient levels releases Inhibition, it does not mean that allelopathy was inoperative under the original conditions. These instances simply illustrate the importance of the Interaction of the two stress conditions. 

Shilling DG, Liebl RA, Worsham AD (1985) Rye (Secale cereale L.) and wheat (Triticum aestivum L.) mulch the suppression of certain broadleaved weeds and the isolation and identification of phytotoxins. In Thompson AC (ed) The chemistry of allelopathy biochemical interactions among plants. ACS symposium series, vol 268. American Chemical Society, Washington, DC, pp 243-271... 

Suppression of weed growth by some rice varieties is often associated with their tillering characteristics and increase root biomass, which complicates the differentiation of allelopathic effects from competition for resources or superior vigor. In the case of rice, some of the most allelopathic cultivars indeed have larger root masses than non-allelopathic cultivars, but none of the QTLs associated with allelopathy were linked to QTLs associated with root morphology. 

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