Interference between hemp sesbania (Sesbania exaltata) and soybean (Glycine max) in response to irrigation and nitrogen

Abstract

Soybean yield loss from weed interference depends upon weed density and competitiveness of crop and weed species in response to environment. Soil water availability and nitrogen fertility were evaluated for their effect on competitiveness of individual species in field experiments. Early-season temperatures in 1995, which were cool compared to 1994, slowed hemp sesbania growth without affecting soybean growth. This resulted in negligible competition with soybean by hemp sesbania at densities of 3 or 6 plants m−2. In 1994, hemp sesbania grew above the soybean canopy, decreasing soybean light interception 29 to 68%, and reducing soybean yield 30 to 48%. Fertilizer nitrogen increased soybean competitiveness, as indicated by biomass production, only in irrigated plots with hemp sesbania at 3 m−2, but did not affect soybean yield. Apparently, competition for light is a primary cause of soybean yield loss from hemp sesbania infestations. In growth chamber studies, simulating temperatures from the field, hemp sesbania growth was stimulated more by warm temperatures than was soybean. Hemp sesbania and soybean dry weights increased 4.4- and 2.7-fold, respectively, at 30/20 C day/night temperatures compared to 25/15 C.