Above ground, life is apparent. Green plants, colorful flowers, animals and even insects show activity in our daily lives—so much so that people probably don’t give thought to life below the earth’s surface. Life in the soil helps make the living items we see above the surface possible.
“Soils are Living” is the July theme for the 2015 International Year of Soils. Larger animals may rely on soil for shelter. Insects and plants rely on it for nutrients. Microbes—tiny organisms such as bacteria, viruses or fungi that require a microscope to see—even call soil their home.
Tim Todd, an instructor in the Kansas State University Department of Plant Pathology, said the food web in soil is much more intricate than any web above ground. He studies another organism found in soil—nematodes.
“Nematodes are round worms,” Todd said. “Most of them are microscopic. Some are large enough to see with a naked eye. Most live in the soil, but some are parasites to animals and plants.”
Todd studies nematodes as pests of agricultural crops. His research helps develop pest-resistant varieties of crops such as soybeans, to increase farmers’ yields and make agricultural production more efficient and profitable.
The soybean cyst nematode, he said, is the No. 1 pest of soybeans in the United States and has become an increasing problem to Kansas’ soybean farmers.
“It lives in the soil, but it infects seedling soybean roots,” Todd said. “When it does that, it forms a feeding site and disrupts root function. The result of that is smaller, stunted plants, maybe some yellow plants, and certainly reduced yields.”
As this nematode matures, he said, it increases in size to the point you can see it with the naked eye. To test for variety resistance, different varieties are grown in soils infested with the soybean cyst nematode.
When the roots are pulled up and examined, Todd determines if the particular nematode is present. It appears as tiny, bright yellow spots on the soybean roots. Those varieties with little to no evidence of the nematode would be considered a resistant variety and one that farmers would prefer to grow.
Resistant varieties also limit production of the problematic nematode, which helps control its population in the soil, Todd said. Farmers typically see a 10-30 percent soybean yield increase by using a soybean variety that is resistant to nematodes in heavily infested Kansas soils.
“Every crop you can think of has a lot of different pests, including nematodes,” Todd said. “We also work with corn and wheat. Corn and wheat have one particular type of nematode called a root-lesion nematode, which is more common than the soybean cyst nematode. It occurs in nearly every field in the state.”
Unfortunately, there is no resistance for that nematode, Todd said, so scientists have to rely on other methods to help farmers.
“On corn right now, we’re looking at seed treatments,” he said. “Several companies have nematicidal seed treatments out, and we’ve been testing those to see how well they work.”
While Todd studies nematodes mostly as soil-dwelling crop pests, he said not all nematodes are bad. In fact, most are helpful by feeding on microorganisms involved in decomposition and nutrient cycling.
“Bacteria and fungi, for instance, will help decompose dying roots, and all the nutrients contained in that will be recycled back into an available form that the living plant can then use,” Todd said. “Nematodes are an integral part of that process.”
To watch a video interview about “Soils are Living” that features Todd, log on to the K-State Research and Extension YouTube page (https://www.youtube.com/watch?v=KstUbXFFo8I&feature=youtu.be). The Soil Science Society of America has numerous resources for the public, teachers and children about soil and each monthly theme for the International Year of Soils. Log on to www.soils.org.