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Effect of Row Spacing and Genotypic Frequency on the Yield of Soybean Blends¹

The effects of row spacing and genotypic frequency on the yield of soybean (Glycine max (L.) Merr.) blends were evaluated for use in establishing testing procedures for new blends. In 1969 and 1970, ‘Chippewa 64,’ ‘Hark,’ ‘Corsoy,’ ‘Provar,’ and ‘Amsoy’ were evaluated in all possible two-component blends at the frequencies 3:1, 1:1, and 1:3, and in all possible three-component blends in a 1:1:1 frequency. The blends and pure stands were tested for yield in 70- and 100-cm rows.

The average yield response of blends to narrow rows was similar to that of pure cultivars. The average yield increase in 70-cm rows over 100-cm rows was 9.6% for the two-component blends, 10.2% for the three-component blends, and 10.0% for the cultivars in pure stand.

Average compensatory responses (deviations of actual blend yields from the weighted means of their component cultivars in pure stand) were similar for both spacings. The average compensatory response was 69 kg/ha or 2.5% for 100-cm rows and 72 kg/ha or 2.4% for 70-cm rows.

Although row spacing generally did not influence compensatory responses, there were blends that had significant deviations from the expected yield in one spacing but not in the other. Furthermore, the percentage yield differences in two row spacings for a blend could not be consistently estimated from the percentage row-spacing response of its component cultivars. It seems that whenever possible, the compensatory response of a blend and its yield response to different row spacings should be evaluated by testing the blend per se in the row spacings of interest.

In 1971 and 1972, genotypic frequencies in four two-component blends were varied in 10% increments from 100:0 to 0:100. Compensatory responses of the blends were found to be dependent on genotypic frequency. Maximum yields of the blends generally occurred over a limited range of genotypic frequencies. All blends had their highest yields when the highest yielding cultivar made up at least 70% of the blend.

Key Words: Glycine max (L.) Merrill • Heterogeneity • Multiline • Genetic diversity • Intergenotypic competition

² Professor of Agronomy and Collaborator, PSRD, ARS, USDA, and former Graduate Research Assistant (Present address: Est. Exp. Dr. M. A. Cassinoni, Fac. de Agronomia, Paysandu, Uruguay), Iowa State University, Ames, IA 50010.

Received for publication August 16, 1973.