In the Spotlight: Meet researcher April Leytem with USDA in Idaho

DSWR is tapping into the talents of the best and brightest researchers in the U.S. They’re doing work through eight institutions in major dairy-producing regions, from Vermont to California. One of these all-important project partners is April Leytem, a research soil chemist with the USDA Agricultural Research Service (ARS) in Kimberly, Idaho.

Tell us a little bit about you.

I grew up in dairy country in upstate New York, although I worked on a farm raising other large grazing animals, not dairy cows. I have a B.A. in economics from Brandeis University, a master’s degree in international development focusing on natural resource management and a Ph.D. in soil science with a minor in chemistry from North Carolina State University.

I performed my postdoctoral research with Dr. Tom Sims at the University of Delaware, helping to develop a Phosphorus Site Index for the states of Delaware and Maryland. I joined the USDA-ARS in Kimberly, Idaho, in 2001.

My research goal has always been to improve the sustainability of integrated livestock-cropping systems, with a focus on evaluating the whole system from animal nutrition to manure management to crop production. In my career, my work has focused on nutrient cycling and management, emissions of ammonia and greenhouse gases and soil health.

What is your role in Dairy Soil & Water Regeneration?

I lead the research team at Kimberly, Idaho. I am also involved in the day-to-day operations of the research study including soil and plant sampling, application of manures, harvest, gas sampling and anything else that needs to be done on any given day. I also mentor the post doctorates who have worked on the project along with a graduate student and many interns.

What is the focus of your team’s DSWR research?

Manure treatment technologies, such as anaerobic digestion, flocculated solids, evaporative solids, solid-liquid separation and advanced treatment systems can all produce nutrient-rich manure-based fertilizers that are more stable and less expensive to transport than fresh manure. These products could enable dairy producers to expand the land on which manure nutrients are applied and improve the sustainability of the dairy industry in the region.

To effectively utilize these manure byproducts, information related to nutrient content and availability as well as potential environmental risks needs to be assessed. In this project, we are investigating the effects of two novel manure-based fertilizer products on nutrient cycling in soils and plants, soil health, crop yield, forage quality and greenhouse gas emissions in semi-arid forage systems with minimum tillage. The two products being evaluated are manure solids from a flocculated solids treatment system and manure solids from an evaporation system. As much of the cropland in the region has a history of manure application, we also tested the performance of these two products on plots that had received a previous manure application versus plots that had not.

In addition, we are evaluating the fertilizer value of these products to help valorize novel manure-based fertilizer products which could provide additional income streams for producers. The goal is to provide producers with information and guidelines for use of these products in regional cropping systems.

What have you learned so far?

Yields of silage corn and triticale were similar among treatments within each year. Over time, yields did decline in control plots that had received no nutrient application since 2020. Yields of silage corn in 2024 appear to be lower than the three previous years which was partly due to planting into the heavy residue left on the plots as they have not been tilled since 2020.

Yield response to nitrogen fertilizer application was greater for the flocculated and evaporation solids than just fertilizer addition alone, indicating that these products have other positive benefits on crop growth in addition to being a source of nitrogen. There were few effects of manure byproduct application on any soil properties.

The greatest nitrous oxide fluxes occurred in May, June and July with plots having previous manure application having greater average cumulative fluxes than plots without previous manure application, while average cumulative fluxes in evaporation solids plots were greater than flocculated solids and control plots. Evaporation solids consistently had a greater emission factor (net percent of nitrogen applied lost as nitrous oxide nitrogen), with losses exceeding the Intergovernmental Panel on Climate Change (IPCC) emission factor of 1% following two years of application.

In regions with nutrient imbalances where advanced manure treatment is necessary to export nutrients, nutrient extraction technologies can produce novel manure-based fertilizer products that are beneficial for plant growth but may have different susceptibilities to nitrogen losses, which need to be considered when managing these products.

What excites you about your work on this project?

Technologies that enable dairy producers to better manage their manure nutrients will help them to improve their overall farm sustainability and circularity, safeguard or improve their soil health and protect air and water resources. These technologies may also enable them to produce valuable products that could provide additional income to improve other areas of on-farm management. A better understanding of the characteristics of these products and their value as a fertilizer will enable us to provide recommendations to sustainably use them in cropping systems. I see these technologies as a win-win for producers and consumers.