Effects of Tillage and Plant Distribution On Soybean Light Interception and Yield.

The effect of plant distribution and tillage treatment has not been documented on soybean growth and development in Iowa. The objective was to determine light interception and soybean seed yield using two tillage treatments, two row spacing, and four plant populations. This research was conducted in 2008 near Nevada and Hudson, Iowa. The experimental design was a randomized complete block in a split-split plot arrangement with four replications. Main plots were conventional tillage and no-tillage treatment, sub plots were two row spacing (38- and 76-cm) and the sub-sub plots were four plant populations (185,200; 308,600; 432,100; and 555,600 seeds ha^-1) using cultivar AG2802. Biomass was collected biweekly and light interception was measured using a 1-m light quantum sensor (Licor LI-191). The data from Nevada was lost in 2008 because of excessive flooding. At Hudson, no interactions were observed between any variables. Tillage treatment and seeding rate did not influence yield. Row spacing influenced yield with 38-cm row spacing yielding 444 kg ha^-1 more than 76-cm row spacing. At R1, light interception was 9% higher in 38-cm rows than in 76-cm rows and continued to be significantly greater until R4. Crop growth rate (R1-R5) was 12 % higher in 38-cm rows than in 76-cm row spacing. In general, canopy biomass per area was greater from R1 through R5 for 38-cm rows compared to 76-cm rows. Research will continue in 2009 and data from both years will be presented.