Effects of Different Sowing Dates on the Growth and Yield of Soybean
1 Tested varieties
(1) Early edamame type: Dalizhuang, Zaosheng Bainiao, Ningshu 60. (2) Summer soybean type: Yudou 16, Huaidou No. 4, Nannong 242, Nannong 86-4, Nannong 88-31, Nannong 96CT-1. (3) Specialty bean type: Danbo Black, Japan 118, Haimen Green, Haixi 13, Black Skin Green Kernel, Lubaozhu. (4) Sprouting bean type: 98-29, 98-30, S-03. Among the above 18 varieties (lines), Zaosheng Bainiao and Ningshu 60 were introduced from the Jiangsu Academy of Agricultural Sciences, the Nannong series were introduced from Nanjing Agricultural University, Dalizhuang, Yudou 16 and Huaidou No. 4 were purchased from the local seed market, and the others were introduced from the Jiangsu Provincial Institute of Agricultural Sciences of the Yanjiang Region.
2 Experimental methods
Each variety (line) was sown in three periods: June 16, July 1, and July 16 (hereinafter referred to as early, middle, and late sowing, respectively). Each plot had sowing rows 5 m long, arranged in 4 equal rows, with one replication. The sowing hill spacing was 25 cm; the row spacing for early edamame was 45 cm, and that for other varieties was 60 cm. 3-4 seeds were sown per hill, and after full emergence, 2 seedlings were retained per hill. After thinning, 10 plants of each variety were marked, and growth and development dynamics were regularly investigated. At maturity, the middle 2 rows were harvested to investigate plant traits and yield structure.
3 Experimental results
3.1 Effects of different sowing dates on the growth period of soybean. The growth periods of early edamame, summer soybean, specialty bean, and sprouting bean varieties were 86-109, 85-118, 100-141, and 95-125 d, respectively, and the green pod harvest periods appeared at 50-66, 60-88, 69-98, and 79-105 d after sowing, respectively. There was no obvious regular difference among early edamame varieties or among sowing dates, while the total growth period of the other soybean varieties shortened with delayed sowing dates.
3.2 Effects of different sowing dates on the growth characteristics of soybean. The plant heights of early edamame, summer soybean, specialty bean, and sprouting bean varieties were 34-46, 37-100, 47-97, and 70-134 cm, respectively, and the number of branches per plant was 2-4, 1.7-10, 2.7-7.5, and 2-9.6, respectively. The plant height and branch number of different varieties mostly decreased correspondingly with delayed sowing dates.
3.3 Effects of different sowing dates on the yield structure of soybean. The 100-seed weights of the tested early edamame, summer soybean, specialty bean, and sprouting bean varieties were about 23, 22, 30-55, and 10-13 g, respectively. The number of effective pods per plant was 12-20, 30-85, 19-54, and 50-182, respectively; the number of seeds per pod was 1.75, 1.70, 1.5-2, and 2-2.5, respectively; and the yield per plant was 5-7.8, 12-30, 20-30, and 10-28 g, respectively. Except for 100-seed weight, the other yield structure indicators of the same variety mostly decreased correspondingly with delayed sowing dates.
4 Discussion
The 100-seed weight of the same soybean variety showed no obvious change across different sowing dates, reflecting the stability of variety seed weight. Except for early edamame, the plant height, number of branches per plant, number of pods per plant, and yield per plant of the other soybean varieties mostly decreased with delayed sowing dates. Therefore, in order to obtain higher soybean yield, in the central Jiangsu region, the suitable sowing dates for early edamame, summer soybean, and sprouting bean varieties should be before the end of June, among which the sowing dates for the Nannong series varieties and specialty bean varieties should preferably be before June 20.