The influence of date of planting on yield and selected parameters of growth and development of ten soybean cultivars

An investigation of the effect of cultivars and date of planting on the performance of soybeans (Glycine max (L.) Merr.) was carried out on a Sequatchie loam (Humic hapludult) soil at the Plant Sciences Field Laboratory, Knoxville, in 1978. Ten selected cultivars were planted on five planting dates, spaced two weeks apart. The number of pods, nodes, seeds, and branches, seed weight per plant, plant height, and seed yield generally decreased with later planting dates while seed size did not. The number of days from planting to flowering, pod formation, and maturity also decreased with later planting dates. Maximum lodging occurred in the third planting and minimum lodging in the fifth planting. Pods were concentrated in the upper one-third of the main stem at the early planting dates. However, the number of pods at the middle one-third of the plant increased gradually with delay in planting date. Seed yield was not significantly correlated with the selected parameters of growth and development within each planting date but the correlation was highly significant across all planting dates. Yield was not correlated with seed size. The length of the vegetative period was not significantly correlated with the reproductive period for the first three planting dates but was negatively correlated for the two later planting dates, and positively correlated across all planting dates. Soybean plants from each successive planting date made most of their growth under a shorter photoperiod than those planted at an earlier date. This resulted in a shorter period of vegetative growth before flowering and also a shorter period of reproductive development. The effect was clearly evident in a significant reduction of all plant characters contributing to yield, except size of seed. No single parameter was significantly associated with yielding ability at any given planting date, but when all planting dates were considered there was a strong positive correlation between yield and most characters contributing to yield.