This study was carried out to determine adequate planting date, to compare the growth characteristics between early and late maturing cultivars, and to provide the data for the cultivation techniques of soybean [Glycine max (L.) Merr.] in double cropping system with winter crops on paddy field in Korea. Cultivars were planted on 26 May, 16 June, and 7 July with a planting density of 70cm(row~;widtb)~;~times~;10cm (planting spacing). Seed yield of soybean planted on June 16 and July 7 was approximately 37~%~;and~;53~% , respectively, less than that of conventional planting date of May 26 in Pungsan-namulkong, and planted on June 16 and July 7 was about 30~%~;and~;37~% , respectively, less then that of conventional planting date of May 26 in Hanamkong. The number of pods and seeds per plant decreased as planting date delayed. Seed weight increased in Pungsan-namulkong but decreased in Hannamkong as planting date delayed. The flowering date was late in delayed planting plots, but it was shorted for days from emergence to flowering and from emergence to maturity. The plant height of Hannamkong was greater than Pungsan-namulkong from the emergence to flowering stages, but in contrast, it was greater in Pungsan-namulkong than Hannamkong after flowering stage (50d after emergence) when it planted on May 26. There were no significant differences between two soybean cultivars at planting dates of June 16 and July 7. Leaf number, leaf area, and dry matter were also reduced by late planting, and Both of them were shown in high reduction at the later planting. There was a high significant difference at the flowering (r~;=~;0.87**) and pod formation (r~;=~;0.91**) stages between leaf dry matter and seed yield. Crop growth rate (CGR) was greater at R2~~R3 growth stages compared to R3~~R4~;or~;R4~~R5 growth stages in two soybean cultivars and the greatest CGR was obtained at planting date of May 26 in two soybean cultivars except for R4-R5 growth stage in Pungsan-namulkong. There was a highly significant positive difference between the seed yield and the leaf area index (LAI) across R3 to R4 and R2 to R3 stages. The photosynthetic rate (PN) of the uppermost leaf position had no significant difference among planting dates and between two soybean cultivars. However, PN of the 7th leaf position increased as the planting date delayed.

This experiment was carried out at paddy field (commercial silty loam soil) in the southwestern Korea. Pungsannamulkong, a determinate growth habit, was a relatively high yielding and late maturing cultivar, and Han­namkong, a semi determinate growth habit, was a relatively low yielding and early maturing cultivar. Seeds were sowed at two plants and with a planting density of 70~times10cm on May 26, 2003. Fertilizer was applied prior to planting at a rate of 3.0-3.0-3.4g (N-P2O5-K2O)~;per~;m2 by all basal fertilizations. Experimental design was a randomized complete block with three replications. Seed yield was higher in Pungsannamulkong by 362g per m2 than in Hannamkong of 260g per m2 Also, the number of pod, number of seed, and number of seed per pod were greater in Pungsannamulkong than in Hannamkong. The number of leaves per m2 showed similar with two soybean cultivars up to August 24 but thereafter it decreased in Hannamkong. The leaf area up to August 4 increased in Hannamkong higher than in Pungsannamulkong, but after that time, Pungsannamulkong had greater leaf area than Hannamkong. The shoot and leaf dry matter of two soybean cultivars from June 23 to August 4 were similar but thereafter, Pungsannamulkong had a significantly greater than Hannamkong. Crop growth rate (CGR), relative growth rate (RGR) and net assimilate rate (NAR) for Punsannamulkong were relatively higher than Hannamkong but leaf area ratio (LAR) and specific leaf weight (SLW) showed higher in Hannamkong. Most of leaves distributed in the ranges of 80-90cm and 60-70cm from the soil surface in Punsannamulkong and Hannamkong, respectively. Pods of Punsannamulkong ranged 10-80cm from the soil surface and most of pods were distributed at 40-50cm. Photosynthetic rate at the flowering stage showed a significant difference between cultivars in the upper most leaf position. There was no significant difference of the photosynthetic rate at 7tn leaf at the flowering stage, and the uppermost and 7th leaf position at the seed development stage between two soybean cultivars.

Field studies were conducted in the southeastern Korea (36~circ N) on a commerce silt loam soil at paddy field. Seed were manually planted on 16 July 2003. Plants were planted with plant densities of 70~times 10 cm (row width x plant spacing), 50 x 10 cm, and 30 ~times 10 cm. Two seedlings per hill were taken prior to V3 stage. Fertilizer was applied prior to plant at a rate of 30-30-34 kg (N-~textrmP2~textrmO5 -~textrmK2~textrmO ) per ha. Experimental design was a randomized complete block in a split plot arrangement with three replications. Yield from different planting densities responded similarly in three soybean cultivars and increased when planting density increased. Somyeongkong showed the highest increasing rate of yield about 26% by 338 g ~textrmm-2 at 30 x l0 cm compared to yield of conventional planting density (70 x 10 cm). Also, the planting density significantly affected pod and seed number and seed weight, but not seed per pod. The tallest plant appeared at 30~times 10 cm. The change of leaf area according to days after emergence showed differently in soybean cultivars. The highest and lowest total dry matter production per square meter appeared at 30 x 10 cm and at 70 x 10 cm, respectively. Crop growth rate (CGR) showed greater at R3∼R4 stages compared with V7∼R2 or R2∼R3 growth stages and showed the greatest at 30 x 10 cm in three soybean cultivars. As late planted soybean, there was a significant relation between seed yield and CGR, and leaf area index (LAI) according to planting densities at before and after the flowering stage. Relationship between seed yield and CGR in three planting densities showed a highly significant positive relation (~textrmR2 =0.757) at R3 to R4 stages, and significant relations (~textrmR2 =0.505, 0.617) at V7 to R2 and V2 to V3. Also, there was a highly significant positive difference between seed yield and LAI during R3 to R4 and R2 to R3 stages.