Have you thought about soybean roots?
Palle Pedersen, Soybean Extension Agronomist
Originally published in the Iowa Soybean Review, October 2005

Many of us have just been looking at roots for proper nodulation and cysts from soybean cyst nematode (SCN). However, we have to start focusing even more on root health in the future if we want to get high soybean yields.

I do not think it is an overstatement when I say that many of us have not thought too much about soybean roots. Soybean roots serve as major vegetative organs supplying water, minerals, and substances essential for plant growth and development. Despite these vital contributions, roots are often taken for granted because they are not visible. But, why?

Is it because you do not make much money on soybean, anyway, so you do not want to deal with it? Or is it because you do not want to get out of your truck, away from the AC and get dirty? Or…., yeah I think that I have heard all the excuses. However, I know that many farmers dig up corn roots every year to look at root worm feeding. So why ignore soybean?

I therefore initiated a large research project last year, partly funded by the Iowa Soybean Association, where one of my graduate students is looking at soybean root health in Iowa in relation to management practices, soil type and genetics. We initiated this project, first of all because we have a tremendous lack of knowledge on soybean roots compared to above ground plant parts.

In addition, I feel that we are often losing a lot of "easy" bushels in the way we raise soybean. Often, it is associated with root health. This is a long story, and I may have to go into more detail in a future article. Let's just look at one example that may give you a hint, though.

It was estimated by a checkoff funded project through the United Soybean Board that we lost 126 million bushels to pathogens in the state of Iowa in 2004. That is close to $800 million in farmers' income loss. Of the 126 million bushels, soybean cyst nematodes counted for 38 percent and sudden death syndrome accounted for 14 percent.

On top of that, we can then add Phytophthora root rot and other seedling diseases. More than 50 percent of our yield loss therefore comes from below ground. In states like Illinois it was more than 80 percent.

These are pathogens that we can very easily manage. However, it is important that we understand the interactions below-ground in more detail so our management recommendations can be more straightforward.

The lack of research on soybean root health has been avoided, because this kind of research is very labor intensive. Root tissues are hard to recover from the soil, and a large number of samples are required to account for the variability that is associated with soil research. The physical environment where roots grow is more heterogeneous than the environment where the aboveground part of the plant develops.

The latter introduces many variables that complicate interpretation of results and narrows the inference of field experiments designed to study roots. Although differences in root growth among varieties have been documented, another source of variability comes from cultural practices and soil type. However, we have technologies today that can help us to minimize this variability.

Try to dig up roots where you see soybeans are struggling. If you are doing on-farm research, then investigate the roots in your trials. I know that I have been extremely excited with some of the new soybean cyst nematode resistant varieties and their root development. They have a larger and deeper root development, and greater nodulation because of the larger root surface. I thought it was a flop when I saw it last year - but it is even more clear this year. Go dig please!