Inhibitory Effects of Redroot Pigweed and Crabgrass on Germination and Growth----From Lab To Field

Abstract Interactions between weeds and crops often occur by resource competition or allelopathy. However, it is still unknown how local weed species influence artificially introduced switchgrass. In this study, four experiments were conducted to evaluate the inhibitory effects of redroot pigweed (Amaranthus retroflexus) and crabgrass (Digitaria sanguinalis) on germination and growth of switchgrass, the lowland tetraploid cultivar ‘Alamo’ (Panicum virgatum cv. Alamo). Switchgrass germination was inhibited significantly in Petri dishes, with 48.1% and 33.9% inhibition on germination rate by redroot pigweed and crabgrass root aqueous extracts at 0.1 g·mL− 1 concentration, respectively. Significant inhibitory effects on switchgrass seedling biomass were observed at 5:5 proportion with redroot pigweed and crabgrass in glass jars, with 61.6% and 53.4% inhibition on plant biomass, respectively. Under the same root segregation, redroot pigweed had a stronger inhibitory effect on switchgrass seedling growth than crabgrass. Growth of transplanted switchgrass seedlings was inhibited significantly by local weeds in the field, with 46.2% and 11.7% inhibition on shoot biomass during the first and second growing seasons, respectively. However, no significant growth reduction in switchgrass was detected in the third growing season.