Allelopathy has been suggested as a mechanism of interference in several weed species. Allelochemicals released from certain weed species influence the growth and yield of crop species. Several laboratory studies present circumstantial evidence of the occurrence of allelopathy as a causative agent in weed–crop agroecosystems. Field evidence, however, is still lacking. In this paper, the significance of field studies is argued in terms of a multifaceted approach to allelopathy, and mugwort is used as an example. Previous research demonstrated the allelopathic potential of mugwort; however, experiments were not carried out in a natural environment. Inderjit and Foy (1999) have demonstrated that chemical characteristics (pH, inorganic ions, and phenolics) of soil amended with mugwort leaf leachate were altered when compared to unamended soil. We have analyzed the mugwort-infested field soil and compared its chemical characteristics with those of amended soils. No definite trend, in terms of influence of mugwort on soil chemistry, was observed. Results indicate the importance of field studies in order to obtain ecologically relevant data from laboratory studies. Field situations are often complex in terms of the presence of interfering flora. Cyanobacteria, for example, play an important role in weed–crop interactions in rice paddy soils. Allelochemicals released from weed species present in the paddy field may influence nitrogen-fixing cyanobacteria in addition to their phytotoxic effects to the paddy crop. Significance of phytotoxic effects of weed species on crop growth, and N2-fixing potential of cyanobacteria in paddy soils is discussed.
Nomenclature: Cyanobacteria; mugwort, Artemisia vulgaris L. #3 ARTVU; rice, Orzya sativa L.
Additional index words: Phenolics, soil characteristics, Trifolium pratense.
