Stability of Soybean Harvest Index¹

Abstract

Previous work had indicated that the harvest index within cultivars of soybeans [Glycine max(L.) Merr.] might be fairly stable. Such stability of harvest index would greatly simplify the conceptualization of the influence of seed growth processes on yield. In the studies reported here harvest index of field‐grown soybean plants was measured in response to four types of environmental influence: interplant competition, extended photoperiod, timing of drought stress, and degrees of drought stress (line source irrigation). The experiments included both indeterminate and determinate cultivars, and included both a northern (Ithaca, N.Y.) and southern location (Gainesville, Fla). These experimental conditions resulted in considerable variability in plant sizes within a cultivar but the harvest index (ratio of seed mass to mass of mature plant without fallen leaves and petioles) was stable. Total masses of individual mature ‘Chippewa 64’ and ‘Bragg’ plants varied substantially in response to interplant competition, but harvest index was essentially constant (0.54 and 0.50 for Chippewa 64 and Bragg, respectively) across most of the range of plant sizes. Harvest index of smaller plants was less than for larger plants, but these smaller plants have little influence on total crop yield and harvest index. Extending the photoperiod to 14.5 h throughout the life cycle of six cultivars increasingly delayed ontogenic events as the distance from the photoperiod lamps decreased. However, no influence on harvest index was observed except at the position nearest the lamps where the standard errors of the harvest indices were increased. Harvest index did not respond to differences in the timing of severe drought stress. When rain was withheld from ‘Wilkin’ plants during vegetative growth, flowering, or seed setting, harvest index of individual plants was essentially 0.60. Only those plants stressed late in pod filling had lower harvest index and increased variability in harvest index. Seed yields (Chippewa 64, Wilkin, and ‘Evans’ for three planting dates) decreased substantially as degree of drought stress, induced by increasing distance from a line source irrigation system, increased yet, harvest index changed negligibly with distance from the line source. Thus, we conclude that harvest index is a conservative characteristic within each soybean cultivar.

The Relationship between Dry Matter Increase of Seed and Shoot during the Seed-Filling Period in Three Kinds of Soybeans with Different Growth Habits Subjected to Shading and Thinning

“…Therefore, HI may be stable except when the assimilate during the seed-fi lling period is strongly suppressed by low solar radiation in all cultivars used. Our results were supported by a result that HI is a conservative characteristic among soybean cultivar including determinate and indeterminate types (Spaeth et al, 1984). There was no difference in the response of HI to different light intercept conditions during the seedfi lling period among soybeans with different growth habits, unless dry matter production during the seedfi lling period is strongly suppressed.…”

“…HI in soybean has been considered to be invariable irrespective of growth habit (Spaeth et al, 1984). However, when plants suffer from water (Schapaugh and Wilcox, 1980) or shading (Kakiuchi and Kobata, 2004) stress during the seed-fi lling period, the percentage of the dry weight before the fl owering stage to that of the fi nal plant dry weight becomes higher reducing HI.…”

“…Furthermore, Board and Tan (1995) showed that defoliation treatment during reproductive stages decrease HI. Spaeth et al (1984) showed that HI in the indeterminate soybean was more stable than in the determinate soybean, although Schapaugh and Wilcox (1980) suggested that HI was variable. Therefore, it is unclear whether the stability and response in HI to growth conditions during the seed-fi lling period in determinate and indeterminate soybean cultivars differ.…”

Incorporation of crop phenology in Simple Biosphere Model (SiBcrop) to improve land-atmosphere carbon exchanges from croplands

“…This Harvest Index range fell within the range (i.e. 0.37-0.45) reported by Rao et al (2002) and that reported by Spaeth et al (1984; Harvest Index range 0.25-0.6)). The estimated average root:shoot ratio soybean at harvest was 0.18.…”

Relationship between Phosphorus Accumulation and Dry Matter Production in Soybeans

“…4 and 8). Although harvest index in soybeans is unstable when shoot dry matter at maturity is markedly low, it is stable in many cases, including interplant competition, photoperiod, the timing of drought stress, irrigation rate, and planting density or shading conditions (Spaeth et al, 1984;Kakiuchi and Kobata, 2004). Our results under various P conditions are in agreement with these reports.…”