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Yield and Seed Growth at Various Canopy Locations in a Determinate Soybean Cultivar¹

The purpose of this study was to investigate yield and seed growth in various parts of the canopy of a determinate soybean [Glycine max (L.) Merr.] cultivar. ‘Braxton’ soybeans were grown in a Cecil sandy loam soil (clayey, kaolinitic, thermic Typic Hapludults) with irrigation (I) applied when soil moisture tension exceeded 0.02 MPa and no irrigation (NI). Row width was 0.96 m, with intrarow spacings of 51, 102, and 152 mm in 1982 and 51 mm in 1983. Pods sampled during reproductive growth were separated into nine groups on the basis of pod location in one of three strata (based on canopy height) with a further separation into main stem pods or pods on lower, middle, or upper branches. Plot yields averaged 3068 and 1400 kg ha^–1 for the I and NI treatments, respectively. Intrarow spacing did not significantly influence yield. Yield in the upper canopy stratum increased from 33% of total crop yield in the NI treatment to 42% in the I treatment. With an increase in intrarow spacing from 51 to 152 mm, the relative yield contribution of main stems decreased from 31% of total yield to 15% while that of lower branches increased from 48 to 66%. Most pod groups did not differ in single seed weight, seeds per pod, or seed growth rate. These averaged 151 mg seed^–1, 2.02, and 3.97 mg seed^–1 day^–1, respectively. It was concluded that both irrigation and intrarow spacing influenced distribution of yield on branches and that yield increases in I soybeans were associated with increases in pod number and in percentage of total crop yield in the upper canopy.

Key Words: Glycine max (L.) Merr. • Irrigation • Plant population density • Reproductive growth • Yield component analysis

² Associate professor, Dep. of Agronomy and Soils, Clemson Univ., Clemson, SC 29631.

Received for publication October 9, 1984.