Weed shift in a maize ( Zea mays L.) — Sunflower ( Helianthus annuus L.) cropping system

A field experiment was conducted during the kharif (June–September) and rabi (October–January) seasons of 2005–2006 to study the effect of a maize — sunflower cropping system on the weed flora shift. The results revealed a change in weed species, i.e. the appearance of new species and the elimination of certain weed species due to the cropping system. The density of Dinebra retroflexa was high during the 1 st year maize cropping period, but Panicum repens became dominant when sunflower was grown after maize. Cyperus rotundus , originally the dominant sedge, was smothered by Cynodon dactylon due to zero tillage. Dactyloctenium aegyptium was the dominant weed species in maize, while Parthenium hysterophorus was the dominant weed species in sunflower. The proportions of Datura fastuosa, Parthenium hysterophorus, Trianthema portulacastrum, Amaranthus viridis, Amaranthus polygamus, Flaveria austerlagica, Gynandropsis pentaphylla and Portulaca quadrifida were higher during the 1 st year maize cropping season, while later their density was gradually reduced due to the inclusion of sunflower in the system.