Seed zinc of soybean as an indicator of zinc status of the mother plant

Evaluation of soybean (Glycine max L.) genotypes for iron (Fe) deficiency can be influenced by zinc (Zn) deficiency. Post-harvest analysis for seed-Zn concentration [Zn] is one way to assess the likelihood that Zn deficiency interfered with genotype assessment. A greenhouse study was conducted on a calcareous soil low in available Zn to determine the influence of ZnSO4 (0, 1, 2, 4, and 8 mg Zn kg(-1)) on growth and seed [Zn] of three soybean genotypes differing in seed size (BS-8920H-large; MK1009HP-intermediate; and EX9228N-small). Maximum seed yields were obtained with 2 mg ZnSO4-Zn kg(-1) for all three genotypes. Severity of Zn-deficiency symptoms in the absence of Zn fertilizer was less pronounced in BS-8920H than in MK1009HP and EX9228N. The relative response to Zn fertilizer was also least with BS-8920H, the large-seeded genotype. However, critical seed [Zn] values were similar for the three genotypes. Seed [Zn] of 31 to 33 mg Zn kg(-1) or greater indicated that seed yield was not affected by Zn deficiency. This adequacy range for seed [Zn] was markedly lower than a reportedly critical seed [Zn] value for soybean of 43 mg Zn kg(-1). Seed [Zn] was determined in 27 soybean genotypes from two yield trials conducted on calcareous soils with 0.60 and 0.45 mg DTPA-Zn kg(-1), respectively. Seed [Zn] data indicated that Zn deficiency had possibly affected seed yields of some genotypes at the lower soil-Zn site.