The partitioning coefficient is defined as the proportion of new dry matter partitioned among different plant parts. Partitioning coefficients can be used to model plant dry matter accumulation. In 1994 and 1995, field studies were conducted at two locations near Manhattan, KS, to determine the influence of density and relative time of emergence of redroot pigweed on dry matter partitioning to stem, leaves, and reproductive parts throughout the season. Redroot pigweed was grown with sorghum and in monoculture at densities of 2, 4, and 12 plants m⁻¹ of row each year at each location. Dry matter partitioning during vegetative growth was not influenced by plant density. However, partition coefficients during the reproductive growth stage changed as a linear function of the time of pigweed emergence relative to the sorghum leaf stage. The later the emergence time relative to sorghum leaf stage, the higher the partitioning coefficient values for leaf (PC_leaf) and stem (PC_stem) and the lower the partitioning coefficient values for reproductive parts (PC_rp). The observed differences in partitioning coefficients due to relative emergence time are valuable information to those interested in simulating growth of competing plant species, especially with reference to their seed production.

Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) ECHCG; common lambsquarters, Chenopodium album L. CHEAL; redroot pigweed, Amaranthus retroflexus L. AMARE; sorghum, Sorghum bicolor (L.) Moench.