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Soybean

Iron Acquisition of Three Soybean Varieties Grown at Five Seeding Densities and Five Rates of Fe–EDDHA

University of Minnesota, Northwest Research and Outreach Center, Crookston, MN 56716

^* Corresponding author (wiers003{at}umn.edu)

Received for publication September 25, 2006. Iron deficiency is a major, yield-limiting factor for large areas of soybean [Glycine max (L.) Merr.] production in the North Central USA. Our objective was to evaluate the effectiveness of increasing both seeding density and rate of Fe–EDDHA in reducing early season (V2–V3) visual chlorosis scores (VCSs) and increasing seed number and grain yield. These measures were judged to reflect differences in Fe acquisition, manifest at maturity as seed Fe concentration (seed [Fe]). Three varieties (Vs), five seeding densities (SDs), and five seed-applied Fe–EDDHA rates (IRs) were evaluated during 2000, 2001, and 2002. With mild to moderate Fe deficiency, applying Fe–EDDHA at planting markedly reduced early season VCSs, slightly increased seed number and grain yield, and had a similarly small influence on seed Fe concentration (seed [Fe]). In contrast, increasing SD had little influence on early season VCSs, but increased seed [Fe] as well as seed number and grain yield. Resistant and susceptible varieties differed in their response to increasing SDs and indicated that the more susceptible varieties (‘Daksoy’ and ‘Jim’) responded to increasing SD to a greater extent than the more resistant variety, ‘Corona’. Nonetheless, Corona's seed [Fe] usually exceeded that of Daksoy and Jim, whether in the near absence of Fe deficiency or in the presence of mild to moderate Fe deficiency. Fe acquisition, measured as seed [Fe], appeared to be regulated primarily by genotype, yet Fe acquisition of less Fe-efficient varieties could be increased by increasing SD or reducing the severity of Fe deficiency.

Abbreviations: IDC, iron deficiency chlorosis • IR, iron rate • SD, seeding density • Seed [Fe], seed iron concentration • V, variety • VCS, visual chlorosis score