Growth and Yield Response of Solid-Seeded Soybean to Early Season Stand Reduction
1987
Torri, K. | Vasilas, B. L. | Carmen, S. G. | Smyth, C. A.
Soybean [Glycine max (L.) Merr.] stands can be reduced by hail storms, soil crusting, poor seed vigor, and other factors. Little information is available on the response of solid-seeded (drilled) soybean to stand reduction. Four experiments were conducted at the University of Illinois on a Drummer silty clay loam (Typic Haplaquoll) in 1984 and on a Flanagan silt loam (Aquic Argiudoll) in 1985 to evaluate the growth, yield, and yield component response of solidseeded soybean to early season stand reduction. Four levels of stand reduction (0, 25, 50, 75%) were imposed at two growth stages (V3, V6) on ‘Hobbit’ (determinate, semidwarf, Maturity Group III) and ‘Pella’ (indeterminate, normal height, Maturity Group III) soybean, planted on 16 May 1984 and 13 May 1985 in 0.175-m-wide rows with a seeding rate of 560 000 seed ha⁻¹. With a few exceptions, the growth stage at which stand reduction treatments were imposed did not affect the parameters measured. Seed yields of Pella in 1985 were constant over a population range of 130 000 to 468 000 plants ha⁻¹. Averaged across the two growth stages, 75% stand reduction, which reduced the population to an average of 118000 remaining plants ha⁻¹, reduced yields of Hobbit in 1984 and 1985, and Pella in 1984 by 11, 14, and 15%, respectively. Across experiments, a population of 308600 plants ha⁻¹ was found to be adequate for maximum yields. Yield reductions in Hobbit were associated with decreased seed number; yield reductions in Pella were associated with decreased seed size. Seventy-five percent stand reduction delayed canopy closure and increased branch number per plant in all cases, and increased internode number per plant in Pella.
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