Growth traits and sink capacity in late sown soybean cultivars with different stem lengths

Soybeans (Glycine max L. Merr.) late planted are sown as a double cropping, which causes a short growing period. Because of the short season, growers employ high plant density (PD) of cultivars developed primarily for a full-season's growth to compensate a potential loss of seed yield. The objective of this study was to examine the effects of two plant densities and soybean cultivars having various stem lengths as growth characteristics and to determine some casual relationships of the growth characteristics and seed yield for the development of breeding strategies. All cultivars in high PD significantly (P<0.05) reduced in leaf area (48.0-70.7%), dry weights of leaves (1.8-44.2%) and stems (14.0-54.0%). Short stem cultivars (Camp and HS 287) significantly (P< 0.05) increased in the number of pods at the upper nodes (3.1-15.6%) and in number of pods carried on the main stem (70.0-86.4%) as PD increased. Larger decline in sink capacity (seed g plant^-1) was observed in long stem (38.9-75.8%) than in short stem (30.0-38.2%) cultivars, but dry biomass apparently increased in all cultivars, ranging from 8.2 to 53.1%. Biomass of short stem cultivar Camp significantly increased from 7,240 to 11,082 kg ha ^-1 (53.1% increased) in high PD. Harvest index (HI) increased in most short stem cultivars in high PD. Seed yield (kg ha^-1) of all cultivars increased (3.9-14.8%) in high PD, particularly short stem cultivars, Camp and HS 287. The major components for increased seed yield in high PD were an increase in the number of pods per unit area and the number of pods of the main stem in late planted soybeans.