Interaction of rapeseed (Brassica naphus L.) residue management and smother crops for weed control in corn (Zea mays L.) and soybean (Glycine max (L.) Merr.);

A series of field experiments on soybean and corn was conducted at the Agronomy and Agricultural Engineering Research Center near Boone, Iowa during 1996 and 1997. Growth chamber experiments on rapeseed germination and establishment were also conducted in 1998. Objectives of the field experiments were to: (a) determine the feasibility of establishing rapeseed early in the spring; (b) determine the effect of rapeseed residue management on weed population dynamics; and (c) evaluate sava medic and berseem clover as smother crops and compare their use with other weed control practices such as herbicides and cultivation. The effect of temperature, fungicide seed coating, and fertilizer on rapeseed emergence and growth was studied in growth chamber experiments.; Field experiments indicated that rapeseed reduced the density and growth of weeds, smother crops, soybean, and corn, particularly when the residues remained on the soil surface. Rapeseed residues and weed control practices affected soybean and corn productivity directly by the weed control provided and indirectly by the interference caused to the crops. Rapeseed establishment early in the spring, smother crops, herbicides and cultivation may be alternatives for weed control in soybean and corn.; Cold temperatures delayed emergence of rapeseed in growth chamber experiments. Rapeseed emergence and growth rates were greater at 10 C than at 5 C. Phosphate fertilization and seed coating with fungicides enhanced rapeseed emergence and growth.; Cover crops established early in the spring are potentially a tool for weed control when combined with cultivation or herbicides. Further work should be done to improve cover crop establishment by selecting a wider number of candidate species, improving the adaptability of those locally promising species through a breeding program and by agronomic practices such as planting date, residue management, tillage systems, soil amendments, and other practices.