Plant Density Effect on Reduced Linolenic Acid Soybean Cultivars

Demand for soybean [Glycine max (L.) Merr.] with modified oil composition has led to the development of new soybean cultivars with reduced levels of linolenic acid. The objective of this study was to determine the effect of plant density on linolenic acid of soybean bred to have reduced linolenic acid concentration (30 g kg–1, low-linolenic) and of traditional soybean cultivars (70 g kg–1, high-linolenic). Low-linolenic and high-linolenic soybean cultivars were planted at four seeding rates of 185,300; 308,900; 432,400; and 556,000 seeds ha–1 at two Iowa locations in 2007 and 2008. Seeding rates did not influence linolenic acid concentration. No yield difference was observed between high-linolenic and low-linolenic cultivars. A 155 kg ha–1 yield loss was observed for both low-linolenic and high-linolenic cultivars at the 185,300 seeds ha–1 seeding rate. Across cultivars, seed mass of mainstem seed was greater than seed mass of branch seed at all seeding rates except the 185,300 seeds ha–1 rate. Regardless of cultivars, increasing plant density had the effect of increasing mainstem seed protein and decreasing mainstem seed oil. Linolenic acid concentration was greater for branch seeds compared with mainstem seeds and the effect was similar between cultivars and seeding rates. Greater linolenic acid concentration for branch seeds was not sufficient to modify the linolenic concentration of the entire seed pool because branch seeds contribute a smaller portion of the total seed mass. These data suggest that low-linolenic and high-linolenic cultivars respond similarly to changing seeding rates both in yield and linolenic acid concentration.