Iowa State University Research Shows Environmental, Yield Benefits of Early Soybean Planting

By Brooklyn Draisey

As Iowa and the U.S. begin to rely more heavily on renewable energy sources, the greenhouse gas emissions from industries like agriculture are starting to take on greater significance.

Michael Castellano, an agronomy professor at Iowa State University, and a team of researchers are hoping to lower emissions from a previously unexplored area of agriculture through research into soybean planting and production.

“We have great interest in making sure all of our crops have low greenhouse gas emissions footprints, and we felt like the first step to mitigating greenhouse gas emissions from soybean production was quantifying those emissions,” Castellano said.

Using peer reviewed data, Castellano and his team conducted a meta-analysis of nitrous oxide emissions in the northern Corn Belt to see the average emissions from continuous corn and soybean production and corn-soybean rotation. From there, they figured out what would cause the greatest drops in emissions, and how those practices could be implemented.

Greenhouse gas emissions from the agriculture sector are very different than those from other industries, Castellano said. They are a product of biological processes that are necessary to produce the country’s food, and they aren’t dominated by carbon dioxide.

Emissions from agriculture production make up 10% of all emissions in the U.S., split by halves between methane from livestock and nitrous oxide from crop production. Nitrous oxide is the most common emission from corn and soybeans.

Industries that encompass power, transportation and more emit carbon dioxide. Castellano said there are already decarbonization solutions developed to mitigate the greenhouse gas, from solar to wind and other alternatives.

“As those sectors begin to decarbonize, and they already have, agriculture will become a proportionately larger piece of our greenhouse gas emissions,” Castellano said.

This is true in Iowa as much as it is across the country. Castellano said 30% of Iowa’s emissions come from agriculture, a “piece of the pie” that has only gotten larger as the state has moved ahead of much of the nation in wind energy.

After bringing all the data together, Castellano said the team conducted “process-based ecosystem models,” which allowed them to place different variables and conditions into the data and see how they could impact nitrous oxide emissions.

Research: Lowering Nitrogen Fertilizer Rates Does Not Reduce Emissions

Castellano said they identified some steps in reducing greenhouse gas emissions from the Corn Belt generally, which included rotating corn and soybeans and ensuring that the nitrogen fertilizer used for corn is at the right levels.

When fertilizer rates are optimal, Castellano said around 60% of emissions in a two-year crop rotation come from corn and the rest from soybeans. Lowering the fertilizer rates below where they need to be for ideal yield doesn’t help lower emissions or change the proportion of where they’re coming from, so further solutions needed to be found.

Earlier Soybean Planting Reduces Emissions

The team identified two ways to reduce emissions in soybean production, the most important being planting soybeans earlier in the season. Castellano said when the soil is left unsown for too long, the nitrogen it produces can go into the atmosphere and waterways.

“By using that nitrogen, by planting longer varieties earlier in the growing season, we can get that nitrogen into the crop where it’s increasing yield and avoiding environmental losses,” Castellano said.

Fall Cover Crops Also Help, Researchers Say

Another solution is to plant cover crops in the fall, Castellano said.

With the data and solutions in hand, Castellano and his team turned to real-time crop production to see their interventions in action.

“We have experiments where we’re actually making these measurements, including Kentucky, Illinois, Iowa, and Minnesota,” Castellano said. “And initial results of that work are very promising in this crop year.”

Initial results from Iowa crop production where a cover crop was implemented and soybeans were planted earlier have shown that nitrous oxide emissions were reduced by around 15%, Castellano said, and they’re “optimistic” that the interventions they identified will yield similar results in other states.

In addition to lowering emissions, Castellano said the yield from soybean crops increased by around 10%, or six bushels per acre.

What Castellano hopes to see as a result of this research is a greater emphasis on early planting to both reduce environmental nitrogen losses and increase yield, with backing from the USDA. As the USDA sets the earliest crop-insurable planting dates, the organization has “significant power” to turn the tides and allow for earlier planting, despite the potential risk of cold weather impacting crops.

Farmers have been planting soybeans earlier and earlier over the past decade, he said, but in considering the environmental and production rewards of doing so, they should be moved even earlier. According to the Iowa Farm Bureau, the earliest planting date for soybeans in Iowa was April 10 for the most southern areas of the state and April 15 for the rest.

“We want to emphasize that planting soybeans earlier has these environmental benefits and these productivity benefits … it’s great when you can get both of those benefits at the same time,” Castellano said. “And also, as the climate continues to warm, we get warmer springs, which we certainly have been seeing in the northern Corn Belt, the importance of planting earlier is only going to increase.”

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