Michigan’s Thumb area study finds no difference in soybean yield regardless of inoculant treatment

Although three years of study data found no increase in soybean yield with the addition of a Rhizobium inoculant, farmers are still encouraged to inoculate soybeans.

MSU Extension educators in Michigan’s Thumb and Saginaw Valley have studied the use of a soybean inoculant and two dual inoculant/growth promoters/enhancers. In 2008, 2010 and 2011, “Hi Stick” Rhizobium inoculant and “Optimize” Rhizobium inoculant and natural growth enhancer were studied. In 2010 and 2011, “Primo” Rhizobium inoculant and growth promoter was included in the study.

In 2008, Optimize was compared to Hi Stick by itself and mixed with High Stick. Both treatments were compared to a non-treated check. This study was repeated at three sites in the Thumb and was replicated three times at each site in a Randomized Complete Block Design. The trial sites had soybeans planted within the past three years, so the sites would be expected to be populated with Rhizobium bacteria at the time of planting. See Table 1 for results.

Table 1. 2008 Soybean inoculant study.

Treatment

Yield (bu./A)

Control (Untreated)

61.6

Hi Stick

61.7

Optimize

61.7

Both Hi Stick and Optimize Mixed Together

62.2

C.V. 2.9%

LSD @ 0.05 2.2

There was no statistical difference between any of the treatments in 2008.

Again, in 2010 and 2011, Primo was included in the study and there was no treatment where the products were mixed together. In 2010 and 2011, the studies were planted at two sites. Both years the studies were replicated four times at each site in a Randomized Complete Block Design. As in 2008, at each site both years soybeans had been grown in the recent past. See Table 2 for results.

Table 2. 2010 and 2011 inoculant study.

Treatment

2010 Yield (bu./A)

2011 Yield (bu./A)

Two Year Ave. (bu./A)

Control (Untreated)

48.4

52.5

50.5

Hi Stick

47.8

50.3

49.1

Optimize

46.7

51.3

49.0

Primo

48.5

52.2

50.4

C.V.

5.8%

5.1%

LSD @ 0.05

2.9

2.8

Results from each of the three years indicate that neither Hi Stick nor either of the growth promoters/enhancers increased yields. However, it is still a good idea to use an inoculant when planting soybeans, even if soybeans have been planted in a field within the past three years. The risk of poor nodule development is too great given the relatively low expense using an inoculant represents.

Funding from the Michigan Soybean Promotion Committee helped make this study possible.

Related Events

Related Articles

Related Resources