SURFACE WHEAT (TRITICUM-AESTIVUM) RESIDUES, GIANT FOXTAIL (SETARIA-FABERI), AND SOYBEAN (GLYCINE-MAX) YIELD

Experiments were conducted from 1992 through 1994 to determine the eff ect of 0 to 12 Mg ha(-1) of surface wheat residues (SWR) on giant foxt ail density and crown node length, and soybean yield, Giant foxtail de nsity decreased as SWR increased from 0 to 12 Mg ha(-1). SWR of 6 to 1 2 Mg ha(-1) reduced giant foxtail density by 2 to 50% compared to bare soil, The crown node of giant foxtail was 2 cm above the soil surface with 12 Mg ha(-1) of SWR, Frost in 1992 injured soybean more than wee ds in plots with SWR while soybean in soil with no SWR was not injured , In absence of frost in 1993 and 1994, yield of weedy soybean increas ed 20 to 29%, respectively, with the increase of SWR from 0 to 6 Mg ha (-1). In weed-free plots, soybean yield was similar across all SWR lev els, These results confirm the hypothesis that high levels of SWR incr eased soybean yield in weedy plots because of decreased giant foxtail infestation.