Soybean planting depth matters

Planting soybean seed at the proper depth will produce more uniform stands and higher yields.

Soybean seed is very sensitive to planting depth, so producers need to be careful and get their crop off to a good start. Planting depth surveys revealed that only 20 percent of the fields planted with drills were planted at or near the intended depth. An even bigger concern is that in 68 percent of the fields, the seed was planted too deep, a condition known to delay emergence.

Under most conditions, soybeans should be planted between 1 and 1.5 inches deep. As a general rule, plant at the shallower end of the range under the following conditions:

Planting at the deeper end of the range is recommended under the following conditions:

Soybean seed can be planted up to 2 inches deep in sandy soils.

Adequate soil moisture is the most important factor affecting soybean germination. The seed must imbibe (take-in) 50 percent of its weight in moisture in order for the germination process to begin and should not fall below 20 percent after the seed swells and the seed coat splits. This is why agronomists recommend planting soybeans into at least 0.5 inches of moist soil.

Planters typically provide better depth control than drills or air seeders. However, depth control on drills and air seeders equipped with gauge wheels mounted on single disk openers can be greatly improved. The easiest way to accomplish this is by switching to narrow profile gauge wheels. A cheaper and more effective, but also more ambitious option is to reconfigure the planting units on drills or air seeders set up on 7.5inch rows so that none of the gauge wheels run over the old corn row. This procedure is discussed in more detail in the Michigan State University Extension article “Reconfiguring planting units on no-till drills to improve soybean planting performance.”

Taking time to check planting depth is important because planters can also place the seed at the wrong depth. We witnessed this last year (2012) in a field near Imlay City, Mich., where a producer noticed a very uniform and obvious alternating pattern as the soybeans emerged. The soybeans that were planted by the units mounted on the center of the planter emerged two weeks earlier than the soybeans planted by the outer units. The early emerging soybeans were planted 1.5 inches deep and were placed into moisture. The later emerging soybeans were planted at 1 inch deep into dry or marginal moisture conditions.

The producer was convinced that had the field not received a timely rain, the shallow planted soybeans would not have emerged on a timely basis. The local MSU educator, Phil Kaatz, gathered yield data from the two planting depths. The seed that was placed at 1.5 inches deep yielded 1.6 bushels per acre more than the seed that was planted at 1 inch deep.

Adjust your soybean planting equipment as soil and crop residue conditions change and dig up seed frequently to verify that it is placed at the intended depth and into at least 0.5 inches of moist soil.

This article was produced by the SMaRT project (Soybean Management and Research Technology). The SMaRT project was developed to help Michigan producers increase soybean yields and farm profitability. SMaRT is a partnership between MSU Extension and the Michigan Soybean Checkoff program.