In order to determine the optimum plant density in soybean at different planting dates, Hobbit cultivar was planted with four different densities (30, 40, 50 and 60 plants! m2) at three dates (May 22, June 5 and 25) during 1994 in Isfahan University of Technology Research Station. A completely Randomized block design was used with a split-plot arrangement. Main plots represented plant densities while sub-plots planting dates. The treatments were replicated four times. The traits studied were seed yield, yield components,biological yield,harvest index, plant height and height to first node. Experimental results showed that delayed planting caused a decrease in plant height, as well as height to the first nod. An increase in plant density caused increase in the above parameters. Grain yield decreased with delay in planting date but increased with increasing plant density up to 50 plants! m2 on dates May 22 and June 5. Further increase in plant density caused a decrease in grain yield.The overall results suggest that, under Isfahan climatic conditions planting dates between mid May to early June at a plant density of 50 plants!m2 can result in highest grain yield, but by delay in planting date till late June the highest grain yield would be achieved through a plant density of, at least, 60 plants!m2. It appears that planting soybean as a second crop in a rotational cycle may result in a favorable yield as well as cost- benefit efficiency.
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