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ARS Home » Southeast Area » Raleigh, North Carolina » Soybean and Nitrogen Fixation Research » Research » Publications at this Location » Publication #258169
Title: Screening Tactics For Identifying Competitive Soybean Genotypes

Author
item PLACE, G - NORTH CAROLINA STATE UNIVERSITY
item REBERG-HORTON, S - NORTH CAROLINA STATE UNIVERSITY
item CARTER JR, THOMAS
item BRINTON, S - NORTH CAROLINA STATE UNIVERSITY
item SMITH, A - NORTH CAROLINA STATE UNIVERSITY

Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/19/2010
Publication Date: 10/25/2011
Citation: Place, G.T., Reberg-Horton, S.C., Carter Jr, T.E., Brinton, S.R., Smith, A.N. 2011. Screening Tactics For Identifying Competitive Soybean Genotypes. Communications in Soil Science and Plant Analysis. Vol. 42, Issue 21.

Interpretive Summary: Weed control is the biggest obstacle for farmers involved in organic soybean production. One answer to this problem is development of new varieties that compete better with weeds. The most likely approach to more competitive varieties is selection for those that cover the ground sooner after emergence and shade out weeds better. However, to do this, soybean breeders need good screening protocols to identify the most competitive genotypes. This purpose study was to compare two screening methods, determine which was best, and also to determine the optimum time after emergence for screening. The two methods were measurement of a) percent light interception by a soybean canopy using light sensors under the canopy, and b) percent ground cover using overhead photography. Overhead photography turned out to be a more reliable and stable predictor of canopy growth than did light sensors. Photographs taken at 3 weeks after emergence were the best predictors of weed suppression and are recommended as a best protocol for identifying competitive soybean types.

Technical Abstract: Weed control is the biggest obstacle for farmers involved in organic soybean production. One answer to this problem is development of new varieties that compete better with weeds. The most likely approach to more competitive varieties is selection for those that cover the ground sooner after emergence and shade out weeds better. However, to do this, soybean breeders need good screening protocols to identify the most competitive genotypes. This purpose study was to compare two screening methods, determine which was best, and also to determine the optimum time after emergence for screening. The two methods were measurement of a) percent light interception by a soybean canopy using light sensors under the canopy, and b) percent ground cover using overhead photography. In 2007 and 2008 we tested two screening tactics to non-destructively estimate canopy coverage during the first 7 weeks after emergence, the critical period for weed competition. Overhead photography at three and five weeks after emergence and light interception measurements at four and six weeks after emergence were compared in ability to predict soybean and weed biomass at the end of the critical period for weed competition. Photograph digital image processing techniques were compared. Overhead photography at five weeks after emergence was most effective at predicting weed free soybean biomass but overhead photography at three weeks after emergence was best able to predict weed biomass associated with soybean genotypes at the end of the critical period for weed competition.