Factors Associated with Reduced Yields of Delayed Plantings of Soybean¹

Abstract

Field experiments were conducted for four years (1981 to 1984) at Lexington, KY, USA (38° N latitude) to determine the causes of reduced yields associated with delayed plantings of soybean (Glycine max [L.] Merrill). Five cultivars were planted in mid‐May and early July in row spacings ranging from 18 to 89 cm and the plots were irrigated to minimize moisture stress. Yields were significantly reduced by delayed planting because of reductions in the number of seed m−2 and mass seed−1. The yield reduction under irrigation indicates that moisture stress is not a major cause of reduced yields from delayed plantings. The reductions in seed number were associated with lower insolation interception during flowering and pod set and with smaller vegetative mass (g m−2) at growth stage R5 (beginning seed fill). The data suggest that a vegetative mass at R5 greater than that required to intercept 90 % or more of incident insolation is required to maximize seed number. The length of the seed filling period was not affected by planting date. Mass seed−1 was positively related to mean air temperature during seed filling, which suggests that the smaller seed from delayed plantings are a result of the lower temperatures associated with the later maturity.

Métodos para a estimativa do potencial de rendimento da soja durante a ontogenia

“…Além destas, Egli et al (1987) ressaltam a necessidade de se ter 500 g m -2 de matéria seca no estádio R5 (início do enchimento de grãos). Para a identificação de lavouras com maior potencial de rendimento, é necessário que se disponha de práti-cas eficientes de manejo capazes de intervir nas mesmas.…”

Untitled

“…1 (Egli et al, 1987). Research from Wisconsin demonstrated that consistent yields across a range of environmental factors were associated with TDM(R5) above 500 g m 2 (Pedersen and Lauer, 2004).…”

Genotypic Adaptation of Soybean to Late Sowing in Southwestern Japan

“…Matsumoto and Umezaki(1987) pointed out that the soybean cultivars with a large seed number but relatively small seed size are more adaptive to late sowing because they easily produce adequate number of seeds. The determination of seed number may play an important role in the response to late sowing (Egli et al, 1987;Steel and Grabau, 1997;Egli and Bruening, 2000). Therefore, genetic improvements for late-sowing soybean seed yields may depend on selection for seed or pod numbers with longer seed-filling periods.…”

“…This reduces the vegetative mass that would contribute to yield production (Egli et al, 1987) and eventually lowers seed yield (Boerma and Ashley, 1982). Earlier flowering is caused mainly by a shorter day length (Board and Settimi, 1986;Zhang, 2006) or by a combination of short day length and high temperature (Board and Hall, 1984) during the vegetative and early reproductive periods.…”