Allelopathic interference of residues of Ageratum conyzoides

Abstract

Ageratum conyzoides L. (Family Asteraceae) is an annual invasive weed native to tropical America. It has now spread to various cultivated and uncultivated areas in the hilly tracts of North India. Primarily, being an agricultural weed, it invades the cultivated fields very fast, competes with crops reducing their quality and productivity. At the end of growing season, a large amount of weed residues are left in the area of its infestation and these interfere with the growth of the crops grown in succession. A study was therefore undertaken to explore the allelopathic potential of the residues of A. conyzoides and to find out whether the observed allelopathic effects are directly due to allelochemicals or through changes in soil nutrient status caused by them. For this, soils were amended with different amount of weed residues and their effect was studied on the growth and establishment of maize and rice. The growth of both the test crops was found to be significantly retarded in the amended soil compared to unamended ones. The amended and unamended soils were also analyzed for pH, electrical conductivity, organic matter, and available macro-nutrients. The amended soils were found to be richer in phenolics, the known phytotoxins. The nutrient status of the amended soils was altered and it correlated with the amount of residue incorporation. Based on the studies it was concluded that A. conyzoides residues affect the growth of test species by releasing phenolics, which interfere with the nutrient status of the soils.