Heat, drought slow progress on inoculation effectiveness study

Kansas State University Distinguished Professor Chuck Rice included a word you don’t always see in research titles when he presented his study to the Kansas Soybean Expo in Topeka on Jan. 9.

“Soybean Inoculant Trials and Tribulations,” was the title of Rice’s presentation.

“When you look at the weather of 2011 and 2012 when these studies were conducted, it’s not hard to see where the tribulations came in,” Rice explained. “Our yield results were very challenged by the growing conditions.”

The research the Soybean Commission asked Rice and his graduate assistants to do would ordinarily have produced conclusive agronomic and yield results. The project was testing whether or not seed inoculants would improve nitrogen-fixing nodulation in soybean fields.

“Soybean acreage in Kansas is expanding,” Rice said. “That means that a lot of soybean acreage is land that has not seen previous production. And since soybeans are not a native plant, it means the rhizobia that are a necessary part of the process are often not present in the soil, or are present in numbers too low to be effective.”

That is why the Kansas Soybean Commission wanted to study the effectiveness of seed inoculants in promoting better nodulation.

Key Points

• Soybean Commission’s inoculant study hampered by growing-season challenges.

• Heat and drought reduce nodulation of soybeans.

• Inoculants are less important than growing conditions and soybean rotation.

Nodulation, the formation of nitrogen-fixing nodules on soybean roots, provides the nitrogen necessary to successful production of grain in the soybean plant. Without nodulation, the plant becomes nitrogen-deficient.

A number of factors can affect nodulation, Rice told the expo attendees. Among the greatest factors are soil that is too hot and too dry — factors that were definitely present in 2011 and 2012 and that skewed the results of how much inoculation might help in more typical growing years.

Effectiveness of inoculation can also be hampered by selecting the wrong strain of rhizobia, poor storage conditions for the inoculants prior to application, poor handling of inoculants, insufficient coverage and existing quantities of inorganic nitrogen in the soil.

“The presence of inorganic nitrogen is especially a factor,” Rice said. “If you have residual fertilizer, it can actually inhibit the formation of nitrogen-fixing nodules on the soybean root.”

Handling and storage counts, he said, because the rhizobia are living organisms.

Eleven field locations were chosen for the inoculation experiments; three of them had soybeans in recent rotations, the remaining eight had not.

The results of the studies clearly showed that there was an added benefit to nodule formation by using inoculation in fields that had not been in regular soybean rotation. There was little to no benefit from inoculation in fields where soybeans were regularly grown.

Rice said a variety of inoculants were tested, including those from Becker Underwood, Novozymes, ABM and TerraMax. All of the inoculants showed positive results on ground where soybeans had not been grown, but the best results were with Becker Underwood and Novozymes products, he said.

“I think the real question for producers is not which product to use, but whether or not to inoculate,” he said. “You can trust your seed provider to know which inoculant will work in your area of the state. The product doesn’t matter as much as whether or not soybeans have been grown recently.”

Trials also showed that in years when heat and drought are prevalent, nodulation is going to suffer, regardless of what product you use, he said.

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EXPLAINING RESEARCH: Kansas State University Distinguished Professor Chuck Rice explains how weather conditions complicated the results of a research project on the impact of inoculation on nodulation in soybeans.

This article published in the February, 2013 edition of KANSAS FARMER.

All rights reserved. Copyright Farm Progress Cos. 2013.