Effect of common cocklebur density on biological yield of maize at varying populations

Experiments were conducted in the Khyber Pakhtunkhwa Province, Peshawar, Pakistan during 2006 and 2007 to evaluate the impact of common cocklebur densities on leaf area, leaf area index, plant height and biological yield of maize using an open pollinated variety "Azam". Seven cocklebur densities (0, 2, 4, 6, 8, 10, and 12 plants m-2) in maize planted at four densities (5, 7.5, 10, and 12.5 plants m-2) were evaluated in a split plot experiment. Statistical analysis for both years indicated significant main effects and interactions for leaf area, LAI, plant height and biological yield of maize. The leaf area of maize was decreased with increase in maize density because of the intra-specific competition within the maize plants. Maize leaf area per plant at all the maize densities was decreased by the density of cocklebur; however, the magnitude of reduction in leaf area was dependent on maize density; the lower the maize density the higher was the magnitude of reduction in maize leaf area. Similarly, the maize LAI at alternating maize densities was linearly affected by steadily increasing the cocklebur density. Increasing cocklebur density and/or maize density increased maize plant height but at very high densities of either species the average maize plant height was decreased as a result of increased intra as well as inter-specific competition period. The statistical analysis also showed that maize biomass declined linearly as weed density increased from 0 to 12 plants m-2, with an increasing rate of decline for high maize densities and low maize densities. Results decide that the effect of common cocklebur interference on maize biomass and other parameters was associated with a change in distribution of resources, resulting in increased crop height at the expense of a reduction in LAI by the crop as weed density increased.