Wednesday, November 15, 2006

Soybean Yield Response to Leaf Defoliation.

Burton L. Johnson, North Dakota State Univ, 1301 12th Ave. N., Fargo, ND 58105, Paula J. Petersen, North Dakota State Univ., 1301 12th Ave. N., Fargo, ND 58105, and Mark E. Zarnstorff, National Crop Insurance Serv., 7201 West 129th St., Suite 200, Overland Park, KS 66210-1567.

Recent expansion of soybean [Glycine max (L.) Merr.] production in North Dakota prompts in-state evaluation of crop response to physical damage for aiding crop insurance yield loss assessment.  The study objective was to determine the influence of growth stage and plant defoliation on soybean yield.  Field evaluations were conducted at a dryland site near Prosper, ND, during 2002, 2003, and 2004 with the glyphosate-resistant soybean cultivar RG200-RR.  The experiment was a RCBD in a factorial arrangement (2 x 4) with four replicates.  Factors included growth stage (R1 and R4) of treatment and leaf defoliation at levels 0, 33, 66, and 100%.  The stage by defoliation interaction for yield indicated defoliation effects only at the R4 stage where yield was reduced 13 and 56%, at 66 and 100% defoliation levels, respectively.  The yield component most affected by defoliation was pods/plant, followed by seed weight, and seeds/pod.  Defoliation reduced aboveground plant biomass but not harvest index.