Defoliation and Stand Reduction Effect On Low-Linolenic Soybean.

Recently, soybean [Glycine max L. (Merr.)] soybean cultivars have been developed with reduced levels of linolenic fatty acid. No information exists for these cultivars regarding seed composition changes due to defoliation and stand reduction during the season. Therefore, the objective of this study was to determine the effect of defoliation and stand reduction on grain composition in low-linolenic soybeans compared to conventional soybeans. Research was conducted in Iowa and Minnesota in 2008. Experimental design was a randomized complete block with four replications using two cultivars (a low-linolenic cultivar AG2222V and a conventional cultivar AG2108) and thirteen treatment from combinations of stand reduction and defoliation (0, 33, 66, 100% defoliation and 33% defoliation + 50% stand reduction) at growth stages V3, V6, and R3. Plots were 3 by 7.6 m, seeded at 371,000 seeds ha^-1, and thinned to 240,000 plants ha^-1. Our preliminary results indicate that low-linolenic cultivars respond to treatments similar to conventional cultivars. Yield decreased as defoliation increased and the yield reduction from defoliation was greater at R3>V6>V3. Linolenic acid content was influenced by defoliation and timing the effect was not different for lo-linolenic cultivars. Our results suggest that low-linolenic cultivars do not respond differently to defoliation and stand reduction than conventional soybean cultivars. This study will be conducted in 2009 and data from both years will be presented.