Sunflowers Support Stronger Soils and Better Yields

By Scout Nelson

Sunflowers are showing promise as an important part of diverse crop rotations in South Dakota. Research indicates that they can support soil health, crop stability, and farm profitability.

Stan Wise of the South Dakota Soil Health Coalition highlighted the value of diverse crop rotations and soil health practices for producers looking at long-term farm success.

Researchers at the North Central Agricultural Research Laboratory near Brookings have studied crop rotations for many years. One promising system includes corn, soybeans, spring wheat, and sunflowers.

The 26-year rotation study was conducted under no-till conditions. Results show that adding sunflowers and small grains to a traditional corn-soybean rotation can improve several soil health measures.

ARS Soil Microbiologist Michael Lehman’s research showed there are soil health advantages to adding sunflowers and small grains to a traditional corn-soybean rotation.

He has observed increased enzymatic breakdown of residue by microbes in the soil following sunflowers. That’s an indicator of increased microbial activity, which promotes soil aggregation, the accretion of soil into stable clusters which allow for increased water infiltration rates, higher water storage capacities, and reduced erosion.

“How are we demonstrating that it’s improving aggregation? We’ve measured the erodible fraction,” Lehman said. “That decreases when you’re measuring it in the corn phase following sunflower compared to soybean. So that’s good. You want low erodible fraction and higher (microbial) activities. We’ve also looked at carbon mineralization activities. Same pattern with activities increasing in corn after sunflower.”

Sunflowers also support helpful fungi near corn roots. These fungi can help plants access nutrients and water while providing protection from some soil diseases.

“There’s more arbuscular mycorrhizal fungi in the corn following sunflower that are associated with corn roots and are able to mobilize nutrients and water and protect the roots against pathogens,” he said. “And there are less pathogens on the corn following sunflower than the other crops.”

The benefits can also extend to crop yields. ARS Research Agronomist Shannon Osborne said corn in a four-year rotation can maintain stable yields during normal rainfall and perform better during dry periods.

In years with limited rainfall, corn yields average about 35% higher in the four-year rotation than in a corn-soybean rotation.