Organic Matter

What is Organic Matter?

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Soil organic matter encompasses all non-mineral solids in soil, arising from biological tissues, byproducts, and wastes. Soil organic matter includes a range of chemical constituents, from simple sugars to complex molecules and partially decomposed particles. Organic matter imparts a variety of chemical and physical benefits on soil and it is the foundation of the soil food web. Soil organic matter is an important indicator of soil health.

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Regional Educator ResourcesOther Educator ResourcesTechnical Resources
Title Source Resource type and Date Short Summary / Preview
Soil Organic Matter Does Matter University of Minnesota and North Dakota State University Extension Webpage



Explanation of the nature and formation of soil organic matter and overview of soil management influences on soil organic matter pools.

Advanced Soil Organic Matter Management Michigan State University Extension Publication

Feb 2011

This bulletin describes the agronomic practices you can use to build soil organic matter and the science behind the practices.
Soil Organic Carbon Cycle Michigan State University Extension Fact Sheet

Aug 2018


Fact sheet about soil organic carbon and a handout.

Using Manure to Improve Soil Health Livestock and Poultry Environmental Learning Community Extension Webinar

Mar 2019


This webinar looks at current practical research in South Dakota and Michigan related to manure use as it relates to soil health.

Soil organic matter North Dakota State University Extension Webpage



Soil organic matter makes up between 1 and 5% of most soils. This small fraction in the soil alters many soil health parameters and benefits plant productivity.

Particulate Organic Matter – NRCS & others Webpage

Sep 2011


POM is biologically and chemically active and is part of the labile (easily decomposable) pool of soil organic matter (SOM).

Soil Quality Indicators: Biological Indicators and Soil Functions USDA NRCS Fact Sheet

Feb 2015


Soil biological indicators provide insight into the living component of the soil. Similar to physical and chemical indicators, biological indicators have a relationship to soil functions and can evaluate soil functions to assess
soil quality.

Soil Quality Indicators: Particulate Organic Matter USDA NRCS Fact Sheet

Apr 2011


Particulate organic matter (POM) fraction referred to in this document comprises all soil organic matter (SOM) particles less than 2 mm and greater than 0.053 mm in size.

Amount of Organic Matter in Soils SARE Fact Sheet



Anything that adds large amounts of organic residues to a soil may increase organic matter. On the other hand, anything that causes soil organic matter to decompose.

Organic Matter: What It Is and Why It’s So Important SARE Fact Sheet



The living part of soil organic matter includes a wide variety of microorganisms, such as bacteria, viruses, fungi, protozoa, and algae. It even includes plant roots and the insects, earthworms, and larger animals, such as moles, woodchucks, and rabbits that spend some of their time in the soil. The living portion represents about 15% of the total soil organic matter.

Photos on crop residue SARE Image

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Photos on crop residue from SARE Library.

Manure’s Impact on Yield, Nitrogen, and Carbon Soil Health NEXUS Research Summary

May 2018

Manure is often viewed by many as an environmental liability. However, if manure is applied at rates equal to or less than the nitrogen (N) requirement of a crop, can manure produce environmental benefits over commercial fertilizer?
Soil Health – Guides for Educators – Soil Organic Matter USDA NRCS Educator Guide

May 2014

Soil organic matter (SOM) is necessary for all soil functions, and it is the most important indicator of soil health.
Title Source Resource type and date Short Summary
What Does Organic Matter Do In Soil? Noble Research Institute Blog post from an independent research institute

Aug 2001


Soil organic matter is a small, but critical component of the soil. This article demonstrates the value of enhancing soil organic matter for increasing the functionality of soils.

Soil Quality Information Penn State Extension Publication

Aug 2012


Healthy soils yield healthy crops, But what is healthy soil and how do we achieve it?

Soil Organic Matter: The Living, the Dead, and the Very Dead University of Vermont Extension Publication

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Extension guide about Soil Organic Matter (SOM). SOM makes up only a few percent of most soils, but it has a great deal of influence on soil properties, and in turn, agricultural productivity.

Building Healthy Soils University of Tennessee Extension Publication

Sep 2012


Organic matter refers to the portion of soil comprised of living organisms, decaying plant residues, and humus.

Soil pH and Organic Matter Montana State University Extension Publication


After reading this module, the reader should: (1) Know what soil pH is and how it relates to soil acidity, (2) Understand how soil pH affects nutrient availability in the soil, (3) Learn techniques for managing soil pH, (4) Know the soil organic matter cycle, and (5) Understand the role of soil organic matter in nutrient and soil organic carbon management.
Managing Soil Health: Concepts and Practices Penn State Extension Publication

Jul 2017

Information for farmers and gardeners who want to understand the physical, chemical, and biological components of healthy soil and how to manage them.
Managing Soils Penn State Extension Publication

Aug 2012

The goal of good soil management is to meet essential plant needs for water, nutrients, oxygen, and a medium to hold their roots with as little management as possible.
Soil Health University of California University Webpage

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Soil health is the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals, and humans. Oftentimes, the features of healthy soil are related to the organic matter content.
Title Source Resource type and Date Short Summary
Measuring Dissolved and Particulate Organic Carbon (DOC and POC) Science Education Resource Center at Carlton College Blog Post

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Dissolved organic carbon (DOC) is defined as the organic matter that is able to pass through a filter (filters generally range in size between 0.7 and 0.22 um). Conversely, particulate organic carbon (POC) is that carbon that is too large and is filtered out of a sample.

Glossary of Soil Science Terms Soil Science Society of America Definitions

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Soil Organic Matter: The organic fraction of the soil exclusive of undecayed plant and animal residues. See also humus.
Humus: The well decomposed, more or less stable part of the organic matter in mineral soils. Humus is an organic soil material which is also one of the USDA textures of muck (sapric soil material), mucky peat (hemic soil material), or peat (fibric soil material.) Most likely it is muck.

Soil biology and soil organic matter; What do recent discoveries mean for soil management? Washington State University Extension Blog Post

Jun 2019


This blog post describes various recent advances in our understanding of soil organic matter cycling and storage, and management principles to incorporate these advances are suggested.

The importance of soil organic matter Food and Agriculture Organization of the United Nations (FAO) Bulletin



This soils bulletin concentrates on the organic matter dynamics of cropping soils. In brief, it discusses circumstances that deplete organic matter and the negative outcomes of this. The bulletin then moves on to more proactive solutions. It reviews a “basket” of practices in order to show how they can increase organic matter content and discusses the land and cropping benefits that then accrue.

Soil Community Structure, Function, and Spatial Variation in an Organic Agroecosystem SARE Guide Sheet



Farmers are becoming increasingly interested in their soil’s biological status. Nitrogen mineralization, aggregate formation, and pathogen control, along with other soil biological processes, affect farm productivity, and profitability.

Global meta-analysis of the relationship between soil organic matter and crop yields Soil Peer-Reviewed Publication

Jan 2019


Developed a quantitative model exploring how SOM relates to crop yield potential of maize and wheat in light of co-varying factors of management, soil type, and climate. We found that yields of these two crops are on average greater with higher concentrations of SOC (soil organic carbon). However, yield increases level off at ∼2 % SOC.

The Sanborn Field Experiment: Implications for Long-Term Soil Organic Carbon Levels American Society of Agronomy Peer-Reviewed Publication

Jan 2011


It appears that an equilibrium level of SOC for some cropping systems takes about 30 to 40 yr to develop. Initial active carbon (AC) content assessment as a proxy for soil quality shows greater AC with manure and higher input management systems. The AC had a wide seasonal flux within a growing season as a function of temperature and moisture fluxes on microbial activity.

Texture, Climate, and Cultivation Effects on Soil Organic Matter Content in U.S. Grassland Soils American Society of Agronomy Peer-Reviewed Publication

May 1989


The purpose of this study was to evaluate the major controls over soil organic carbon content and to predict regional patterns of carbon in range and cultivated soils. Organic C increased with precipitation and clay content and decreased with temperature.

Developments in Agricultural Soil Quality and Health: Reflections by the Research Committee on Soil Organic Matter Management North Central Education and Research Activity Committee (NCERA-59) Peer-Reviewed Publication

Jul 2019


Article comments on the science supporting soil quality and associated soil health assessment for agricultural lands with the goal of hastening progress in this important field.

Soil Organic Carbon and Nitrogen Feedbacks on Crop Yields under Climate Change Agricultural & Environmental Letters Peer-Reviewed Publication

Aug 2018


A critical omission from climate change impact studies on crop yield is the interaction between soil organic carbon (SOC), nitrogen (N) availability, and carbon dioxide (CO2). We used a multimodel ensemble to predict the effects of SOC and N under different scenarios of temperatures and CO2 concentrations.

Evaluating the impact of soil conservation measures on soil organic carbon at the farm scale Computers and Electronics in Agriculture Peer-Reviewed Publication

Apr 2017


The study compares the CO2 emission and sequestration patterns of agricultural soils.

This page reviewed by Liz Schultheis, Joe Rorick, Caley Gasch, and Anna Cates.

Last reviewed February 29, 2020