THERE IS A trend in modern soybean production to plant soybeans deeper than the traditional 1.5 inches. This trend may be associated with an increased use of planters compared to seed drills. The idea may also be carried over from the well-known fact that shallow planted corn does not establish a proper root structure. The same idea is then transferred to soybeans by some farmers. Placing the seed deeper also results in less temperature variability since soil temperature at two inches is less influenced by cold air than soil closer to the surface. Ontario trials were established to re-examine the best soybean planting depth with modern varieties. The initial results are very clear (see table below). Planting at two inches or deeper reduced plant stands.
A target depth of 1.5 inch strikes a good balance between placing the seed into moisture and not planting it so deep that it runs out of energy before it can emerge. It must be noted that planting half an inch into moisture is always recommended so planting deeper than 1.5 inches in total may be necessary as soils dry out in late spring or early summer. But plant stands will be reduced more from deeper planting especially in soils prone to crusting. (See picture to left).
If sufficient moisture is present and soils are cold, there is also nothing wrong with seeding at one-inch depth, especially in early spring. At present, there is no evidence that a deeper planting depth is necessary for proper root development in soybeans. Many modern varieties have small seed so deeper planting can be problematic. Yield results from this study will be available this fall at www.fieldcropnews.com. •