Sowing date effect on grain soybean has been well documented, while less research was done on vegetable soybean. The impact of sowing date on the duration of critical phonological stages, and the responses of seed growth and marketable yield of four vegetable soybean cultivars with different maturity planted at about 2-weeks intervals over a 6–weeks span in North-eastern USA was investigated. The difference in fresh pod harvest (R6) from the first to the last sowing date ranged from 15 to 30 days. Sowing after June 5th did not shorten the growing period for early maturity cultivar. The later the sowing date, the longer the duration from R6 to mature seed harvest. Seed dry matter accumulation period was extended for one or two more weeks by late sowing. The marketable yield ranged from 4069 to 8660 kg/ha, and the response to sowing date differed among cultivars. Marketable yield decline, per day of sowing delay was 34.4 - 54.9 kgha-1day-1 for three cultivars, while an unexpected rank reversal occurred for brown seed cultivar. Yield decline associated with delayed sowing was primarily related to reduction in standard pod number, while increased fresh seed weight might compensate the yield loss at R6 stage. The insensitivity of yield response to sowing date from early maturity cultivar Dongdou 24, provides farmers flexibility to gain higher economic return.
Key words: Sowing date, growing period, fresh seed weight, standard pod number, vegetable soybean.
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