Distribution Pattern of Yield Components in ‘Braxton’ Soybeans¹

Abstract

Nodal and other distribution patterns of seed yield and yield components are useful in modeling soybean [Glycine max(L.) Merr.] growth, in analyzing the factors responsible for yield differences between experimental treatments, and in predicting yield. The purpose of this study was to determine the influence of irrigation and intrarow spacing on the distribution of yield and yield components in a determinate soybean cultivar. ‘Braxton’ soybeans were grown in 0.91 m rows on a Cecil sandy loam soil (clayey, kaolinitic, thermic Typic Hapludults) at intrarow spacings of 43, 61, 102, and 305 mm between plants and under three irrigation treatments: full‐season irrigation (FSI), irrigation beginning at bloom (BI), and no irrigation (NI). At maturity, samples were collected to determine pod number, seeds per pod, seed number, yield, and single seed weight for the main stem positions at each node and for the branches originating at each node. Branches contributed more pods, seeds, and yield than did main stems in all treatments, while seeds per pod and single seed weight were similar on stems and branches. Increases in intrarow spacing increased seed number and yield on branches and decreased pod number, seed number, and yield on the stems. Irrigation had little influence on the branch/stem ratios of yield components. Full‐season irrigation and BI had greater numbers of pods, numbers of seeds, yield, and seeds per pod on stems and branches and greater single seed weight on stems than did NI. With the exception of stem seeds per pod which was greater for BI, there were no differences between the two irrigated treatments. Seed number, pod number, and yield were maximized in the lower half of the nodes whereas seeds per pod and single seed weight were greatest in the upper nodes. The upper six nodes contributed the least to yield in all treatments. Increases in intrarow spacing increased the contribution of the lower nodes to yield whereas irrigation decreased the relative contribution of the lowest nodal division. We concluded that the large contribution of lower nodes to yield was due to the large proportion of yield borne on branches produced from lower nodes. Increases in spacing resulted in greater contribution to yield of these large branches and thus to a greater concentration of yield at lower nodes. Irrigation influenced distribution of yield through influences on distribution of all yield components.

Drought‐Stress Effects on Branch and Mainstem Seed Yield and Yield Components of Determinate Soybean

“…1) would explain why the two levels of drought‐stress treatment differed in individual seed weight in 1998 but not in 1999. The main stem of determinate soybean generally contributes less to total yield than the branches (Board, 1987; Frederick et al, 1998; Ramseur et al, 1984b). However, our data show that the relative contribution of the mainstem to total seed yield probably depends upon soil water conditions during the growing season.…”

“…A majority of the seed yield of determinate soybean is produced on these branches originating from the main stem (Board, 1987). Unfavorable growing conditions, such as late planting, excessive soil water, and high plant populations, reduce soybean seed yield primarily by reducing branch growth and branch seed yield per plant (Board et al, 1990; Frederick et al, 1998; Linkemer et al, 1998; Ramseur et al, 1984b). Stresses that reduce crop growth rate between Growth Stages R1 and R5 result in the greatest seed‐yield decreases (Board and Harville, 1998; Board and Tan, 1995; Linkemer et al, 1998).…”

“…Less is known about the effects of drought stress on soybean branch growth and branch seed yield or how drought stress affects the distribution of seed yield between the main stem and branches. Ramseur et al (1984a)(b) reported that, for the determinate cultivar Braxton, most seed yield was located on branches originating from lower mainstem nodes and that increases in seed yield with irrigation were due to increases in the number of seeds per square meter and seed weight on both the mainstem and branch fractions. Full‐season irrigation and irrigation beginning at initial flowering had the same effect on seed yield in their study, suggesting that the major factors affecting seed‐yield increases with irrigation do not come into effect until near initial flowering.…”

Flower abscission in soybean as affected by assimilate supply and hormone levels

“…Irrigation during flowering increased pods formed per plant (Ramseur et al, 1984;Kadhem et al, 1985) whereas drought stress during the flowering period reduced pods per plant and yield (Snyder et al, 1982). Abscission of flowers was found to increase when daylength was lengthened (van Schaik and Probst, 1958b).…”

“…In determinate cultivars, the terminal raceme, the top of the main stem and most importantly the branches have contributed to the yield of the plant (Dominguez and Hume, 1978;Ramseur et al, 1984). The total percentage abscission is greater with increased depth into the canopy (Wiebold et.…”