Efficiency is the name of the game in agriculture. Knowing how to get more out of the land is one thing, but understanding what the impacts are to soil, water and inputs is another.
A group of nine researchers is exploring how interseeding may net better yields, environmental outcomes and nutrient uptake when put to work in long-term manure-applied plots in Idaho. Outcomes will inform farmers of ways to be more efficient with corn and alfalfa – but the research team also wants to know the impacts of various growing practices on water, emissions and more.
Pramod Acharya is an assistant professor and extension specialist in forage agronomy with the University of Idaho. He is part of the Emissions and Forage Quality team for the study.
“This is a comprehensive project,” he says. “I am interested in understanding the different mechanisms underlying various production systems; particularly, the differences between interseeding and single seeding. As a forage specialist, I am eager to evaluate how these approaches influence forage productivity, nutritional composition and overall performance. I’m also looking forward to this collaborative effort.” The project is funded for three years beginning in 2026.
“At the end of this project we will have produced findings that answer the research questions from multiple dimensions,” says Acharya.
Gilbert Miito, assistant professor and extension specialist in air quality in dairy sustainability with the University of Idaho is another member of the Emissions and Forage Quality team. He explains that in the late fall of 2025, he and Acharya came together with five others from the University of Idaho, USDA Agriculture Research Service (ARS) and Utah State University (USU) to work on soil and water research. These original team members were joined by the two-member Modelling and Simulation team.
Miito says anticipated study outcomes include, “Addressing concerns in the dairy industry around nitrogen use efficiency, water use efficiency [and] how to promote better use of manure in the industry without impacting the environment.”
The interseeding approach
Acharya’s involvement will be on the cropping side of the study. He explains that the overall goal is to determine whether interseeding alfalfa into corn yields the forage performance and other benefits the team anticipates.
For this study, interseeding is the planting of a corn variety common to the south-central Idaho region planted in standard rows. Once the corn starts to sprout, alfalfa (also a variety common to the region) is planted in the rows between the corn rows.
“Typically, the dairy farmers know how to grow corn. They know how to grow alfalfa. What we would like them to take up is the corn alfalfa interseeding,” says Miito.
The interest in this approach is multi-faceted. With two crops growing at the same time, there is the potential of greater forage yields from the same plot of land. There may also be a more efficient use of soil nutrients, with two crops growing and drawing from the land. For those who have an abundance of manure, or potentially over-applied plots, the crops could help reduce the risks of leaching.
Additionally, because alfalfa can be a slow crop, starting with corn ensures forage production as the alfalfa gets going.
“Alfalfa is challenging,” says Miito. “In the first year, the yields are lower. It’s called the establishment year. You get better yields in the second year.”
In the first year of interseeding, the alfalfa is harvested with the corn, ensuring the benefit of a corn harvest while the alfalfa takes hold. In the second year, the field would be an alfalfa-only harvest.
“You’re getting more yield,” he says.
Years in the making
There are 64 plots at the USDA ARS Kimberly, Idaho site that had been under various manure treatments from 2012 to 2020. The applications were zero, 18, 36 and 52 tons per acre with crop rotations typical for the area. From 2021 to 2025, manure applications ended and the process of a tracked drawdown of nutrients began.
“What happens if you stop applying manure and you just keep the rotation going to see how fast you can use it up?” Miito explains of how the drawdown works.
Following the drawdown, the soil was seen as “nutrient sufficient” and typical for land that had been regularly amended with manure over a number of years.
“After the drawdown, that’s when we came in and decided to start a new rotation,” he says of the corn and alfalfa interseeding trial. “This is more of a dairy-specific rotation. It’s a new rotation that could be a better option for dairy-centric agronomy.”
The 60’ x 40’ replicated plots in the 400’ x 500’ study area are divided into a north field and a south field. The various manure application rates of the 2012 to 2020 study will potentially cause variability in the interseeding study, which led to the need for a significant number of trial plots for comparison purposes.
If, at soil testing stages, nutrients are not sufficient, manure will be applied.
This year will see corn planted in the north field and alfalfa in the south field. Corn and alfalfa will be interseeded in the north field in 2027 and corn only will be planted in the south field (with alfalfa removed). For 2028, alfalfa only will be planted in the north field and corn will be interseeded with alfalfa in the south field. These various approaches will ensure a range of information about crop volumes, nutrient uptake and environmental impacts.
“This year, we are starting off with corn and alfalfa,” says Miito. “Those are going to be our baselines.”
Acharya says the study aligns with work he had done previously. “While previous studies have often examined these components separately, this research integrates multiple disciplines within a single framework.”
The hypothesis
He says other, similar interseeding studies show promising results.
“That’s why we want to test here in the western United States,” he says. “What we are assuming, alfalfa, since it will be in its establishment phase in the first year, it will probably use some nutrients, specifically, phosphorus and potassium. It might impact a little on the corn yield.”
But, he adds that as a legume, alfalfa has many benefits including its deep-reaching roots and ability to build nitrogen in the soil over time. “My interest would be to look at the forage productivity [and] nutrient composition,” he says. “Besides that, we are still looking at nitrogen and water use efficiencies for different cropping systems and management.”
Miito expects nutrient uptake will be higher with two crops, thus less opportunity for leaching, and better water use. “You use the water better, you use the nutrients better and you get more yield,” he says. “You have better root structure because the alfalfa is holding the soil together. You don’t have run-off. We’re just building the problem and the hypothetical solution. Now we have to prove that’s what’s going to happen.”
The expectation is an up to 25 percent reduction of nitrous oxide, improved forage yield and quality and improved water use.
Measurement matters
Plots will be monitored for water balance and nutrient movement with neutron probes and surface TDR sensors. Crop productivity will be assessed through dry matter yield and forage nutritional composition. “We are going to measure all the nutrients, the pre-plant and the post-plant and everything about the soil,” says Miito. “We’re also going to monitor how much water we’re going to apply. And we’re also going to measure emissions – mostly nitrous oxide emissions.”
While the fields are irrigated, there is a theory that less water may be needed for the interseeded plots than the single crop plots. Plus, the impacts irrigation has on emissions will be monitored. He notes that USU is uniquely positioned to evaluate irrigation rate impacts on productivity because the school is doing similar work to this study in Idaho, but with a significant focus on deficit irrigation and overall water use optimization.
“We’re tying it all together,” he says. “In the plots we have the ability to adjust how much water we apply to see how that changes things around. We’re going to have an over-watered application and then a water deficient, just to see what happens.”
The Ruminant Farm Systems model will simulate farm-scale results of the practices trialled. Additional modelling will be conducted using that data along with long-term experimental datasets. These models will provide 20- to 30-year environmental and productivity views.
Through measurement and modelling a robust picture will develop showing how interseeding compares to single crops.
“If you interseed, this is how it compares to corn alone, this is how it compares to alfalfa alone, this is how much nutrients it’s using, this is how much water it’s using and this is the environmental impact,” says Miito of how he sees this study providing farmers with an interseeding how-to guide once results are available.
Field days, to share the information with farmers, are built into the study. Plus, in year three, the modelling will ramp up to show how the results from the trial site can be applied to an operational dairy. •
