Episode 30: What Really Influences Soil Organic Matter?
Season 5
Episode 30
September 22, 2026
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Show Notes
Building soil organic matter has become a common goal for farmers looking to improve soil health, but increasing soil organic matter levels can be harder than we’d expect.
In this episode, host Amy Crozier is joined by Andrew McGuire, Irrigated Cropping Systems Extension Agronomist and Grant County Director with Washington State University, to explore what influences soil organic matter (SOM) and which management practices can actually help build or maintain it over time.
They discuss the balance between biomass inputs and losses, how harvest and erosion affect SOM, the value and limitations of different soil-building practices and debunk the claim that nitrogen fertilizer burns up SOM. Andrew also shares how growers can evaluate soil health products, set realistic expectations and focus on practices that address measurable problems in their fields.
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"If you under fertilize...you get lower yield, less biomass and less organic matter."
About the Guest
Andrew McGuire
Irrigated Cropping Systems Agronomist, Grant County Director, Washington State University Extension
Andrew McGuire serves as an Extension Agronomist and Grant County Director at Washington State University, working with the university’s extension program since 1999, focusing on sustainable solutions for irrigated farming in the Columbia Basin. His work includes developing high residue farming systems, cover cropping strategies and green manure rotations to improve soil health and manage pests. Andrew also writes extensively about agriculture and soil management and is active on social media.
