EFFECT OF CORN-INDUCED SHADING ON DRY-MATTER ACCUMULATION, DISTRIBUTION, AND ARCHITECTURE OF REDROOT PIGWEED (AMARANTHUS-RETROFLEXUS)

A fundamental component of modeling crop interference is the effect of understory photosynthetic photon flux density (PPFD) on weed architec ture and growth. The effect of decreased PPFD on spaced redroot pigwee d dry matter accumulation, distribution, and plant architecture was qu antified by increasing corn density and delaying weed planting date. A s canopy-transmitted PPFD declined, total dry matter accumulation decr eased and relative dry matter distribution was greater to mainstem com ponents than to branch components. Increased rectangularity in underst ory weed architecture was associated with a concomitant decrease in br anch number. The proportion of leaf area and dry matter in the upper s egment of the redroot pigweed increased as PPFD declined with increase d corn density. Results suggest that changes in plant architecture, as influenced by canopy-transmitted PPFD, may be as important as those o f total dry matter and leaf area when describing and predicting the ef fects of crop-weed interference.