Effect of cultivation on allelopathic interference success of the weed,Pluchea lanceolata.

Pluchea lanceolata, a perennial noxious weed, is rapidly spreading into cultivated fields in semiarid regions of India. The objective of the present study was to evaluate the effect of cultivation on the interference success ofPluchea lanceolata by comparing chemical characteristics of the weed and its associated topsoil and subsoil in cultivated and uncultivated habitats. Weed plants from both cultivated and uncultivated habitats were analyzed for four biotic characteristics. Leaves were analyzed for nine chemical characteristics. Soils (topsoil and subsoil) were analyzed for 13 chemical characteristics. Nutrient concentrations of the weed and its associated soils, both in cultivated and uncultivated habitats, showed that plant response with reference to nutrient uptake was inversely related to that of soils. Thus, the weed does not create nutrient stress. With cultivation, leaf area and Cu and Na contents increased, while leaf ash, leaf weight, and Mg and Ca decreased. In the topsoil and subsoil, however, concentrations of total carbonates, total phenolics, and Ca increased with cultivation, while organic carbon, phosphate, and K decreased. High phenolic content of the cultivated fields could be explained due to leaching of water-soluble compounds from the plant parts either through natural leaching or through various agricultural practices such as ploughing and irrigation. We concluded that water-soluble phenolics, leached from the weed into the soil, increased with cultivation.