Tall Waterhemp Competition in Grain Sorghum

Abstract

Grain sorghum (Sorghum vulgare Pers.) was grown in combination with varying densities and durations of tall waterhemp (Acnida altissima Riddell) during 1964 and 1965 at Manhattan, Kansas. As waterhemp density and duration increased, sorghum fodder and grain yields were reduced. Yields of both species and competitive influence of waterhemp were highest during the year of high rainfall and supplemental N fertility. The net competitive influence of waterhemp on sorghum grain was accounted for principally by reduced seed size. Competition for soil moisture in 1965 was greatest when weeds remained full-season, and was most pronounced early in the season at soil depths below 20 inches.