Impact of Auxin (IAA) Spraying and Row Spacing on Soybean Growth and Yield

Abstract A field experiment was applied throughout the summer of 2024 at the Field Crops Research Station, Agriculture College, Tikrit University, to investigate the effect of spraying Indoleacetic acid (IAA), 0, 150, 300, and 450 ppm, and the distance between rows, 30-30, 30-60, 60-60, and 75-75 cm, in the growth and yield of soybean traits. The Randomized Complete Block Design (RCBD) was used to arrange the experiment. Soybean plants sprayed with IAA impacted significantly. The concentration 300 ppm of IAA showed mostly higher chlorophyll (SPAD) (33.49), leaf area (1973.30 cm 2 ), plant height (81.08 cm), pod number (156.80 pods plant −1 ), plant yield (gm plant −1 ), and oil persentage (22.04 %). Similarly, plant distances affect growth and yield traits. Seventy-five centimeters between rows showed mostly higher impact to soybean chlorophyll (SPAD) (33.05), leaf area (2055.30 cm 2 ), plant height (83.33 cm), pod number (171.32 pods plant −1 ), plant yield (50.09 gm plant −1 ), and oil persentage (22.37 %) compared with the other rows distances. The interactions between the two factors (IAA and row spacing) impacted all the study traits. Mostly 300 ppm of IAA and 75 cm between rows was the heighest of all the traits. Although the distance between rows of 75-75 cm recorded the highest values for most of the studied traits, the differences between them and the distance of 60-60 cm were not statistically significant. The results of this study indicate that it can be used to improve soybean cultivation practices in the Tikrit region.