Competition between cowpea and redroot pigweed in response to phosphorus and planting density under field conditions
2007
Biftu, K. N. | Qasem, J. R.
The competitive relationship, yield performance, and dynamics of canopy dominance of cowpea [Vigna sinensis (L.) Savi ex Hassk.] and redroot pigweed (Amaranthus retroflexus L.) grown at different levels of phosphorus (P), planting densities, and density proportions, were studied under field conditions in Summer 2001. Both species behaved differently in response to different planting densities, density proportions, and P treatments. Shoot dry weights (DW) of cowpea increased in line with its proportion in the mixture, and cowpea leaf area was greater than that of A. retroflexus, but the weed over-topped the cowpea plants and established a greater leaf area over the crop canopy. The CO₂ assimilation rate of A. retroflexus was greater than that of cowpea. In mixed stands, A. retroflexus produced relatively higher yields when present in an equal proportion with cowpea, with a relative aggressivity of 0.42. CO₂ assimilation rate was the parameter that contributed most to variations in the shoot DWs of both species. The effect of proportion of the mixed density on shoot DW was due mainly to its effect on the CO₂ exchange rate required for carbohydrate production and growth.
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