Soil 

Quality 

Institute 

Soil Quality Technical Note No. 5 

Managing Soil Organic Matter 

The Key to Air and Water Quality

Technical Note No. 5 

October 2003 

Series written by: 

Soil Quality Institute 

411 S. Donahue Dr. 

Auburn, AL 36832 

334-844-4741 x177

soils.usda.gov/sqi 

Erosion control is not enough 

Soil conservation policy in the United States stems from the 

devastating erosion events of the 1920s and ’30s. Out of 

concern for preserving agricultural productivity came the 

concept of tolerable soil loss and the creation of the T factor – 

the maximum annual soil loss that can occur on a particular 

soil while sustaining long-term agricultural productivity. 

Conservationists focused on reducing soil loss to T by 

applying practices, such as terraces, contour strips, grassed 

waterways, and residue management. 

By the end of the century, concerns about air and water 

quality became as important as concerns about agricultural 

productivity. To address these environmental goals and 

maintain the land’s productive potential, we must now go 

beyond erosion control and manage for soil quality. How soil 

functions on every inch of a farm – not just in buffers or 

waterways – affects erosion rates, agricultural productivity, 

air quality, and water Soil organic matter, Soil quality. The 

most practical way to enhance soil quality today is to promote 

better management of soil organic matter or carbon. In short, 

we should go beyond T and manage for C (carbon). 

Why focus on soil organic matter? 

Many soil properties impact soil quality, but organic matter 

deserves special attention. It affects several critical soil 

functions, can be manipulated by land management practices, 

and is important in most agricultural settings across the 

country. Because organic matter enhances water and nutrient 

holding capacity and improves soil structure, managing for 

soil carbon can enhance productivity and environmental 

quality, and can reduce the severity and costs of natural 

phenomena, such as drought,flood, and disease. In addition, 

increasing soil organic matter levels can reduce atmospheric 

CO2 levels that contribute to climate change. 

Management

Reduced tillage, Cover 

crops, Rotational grazing, 

High biomass rotations 

Soil quality

Soil organic matter, Soil 

structure, Soil Organisms, 

Water holding capacity, 

Infiltration 

Air quality, 

Water quality, 

Productivity

Fewer pollutants, Less 

dust, Less sediment, 

Drought and disease 

resistance 
Go beyond T– Manage for C 

The goal of reducing soil erosion to T (tolerable soil loss rates) generated 

remarkable improvements in the nation’s natural resources (figure 2). We can 

achieve a new level of soil conservation by focusing on building soil organic 

matter or soil carbon (C). 

• By emphasizing organic matter management technology, soil loss can be 

reduced on those lands that still suffer excessive erosion. 

 

• Even moderate erosion rates can harm air quality, water quality, and wildlife 

habitat. Improving soil organic matter levels can further stabilize soil within 

fields and protect environmental quality (figure 3). 

• Keeping soil in place is only the beginning of soil conservation. Soil also has to 

function well. It must hold nitrogen, phosphorus, and pesticides in place and 

keep them out of surface water. Soil must deliver nutrients and water to plants 

as they need them. Soil should minimize the effects of floods and droughts. 

Organic matter helps soil perform all these functions. 

What does this mean for conservation? 

Managing for C means using well-known technology in a new way. By addressing 

conservation issues from the perspective of soil organic matter instead of erosion, 

we will focus on enhancing the soil as opposed to manag-ing for tolerable 

degradation. We will exploit the full potential of cover crops, crop rotations, and 

reduced tillage to address conservation concerns. Moreover, managing for C 

provides additional on-site benefits and incentives for the landowner, creating 

greater motivation for the person making the ultimate decisions about managing the 

Nation’s natural resources. 

Keeping soil in 

place is only the 

beginning of soil 

conservation. 

Soil also has to 

function well. 

*What is SCI? The Soil Conditioning Index (SCI) predicts the effect of cropping systems on soil 

organic matter levels. A positive SCI indicates a cropping system that, if continued, is likely to 

result in increasing levels of soil organic matter. More information about the SCI is at 

http://soils.usda.gov/sqi.
How does organic matter work? 

Once a land manager begins working towards enhancing soil organic matter, 

a series of soil changes and environmental benefits follow (figure 4). The 

rate and degree of these changes and the best suite of practices needed to 

achieve results vary with soil and climate. Initially, managing for greater 

soil organic matter may require higher pesticide, herbicide, or nutrient 

applications. In time, productivity and environmental quality will be 

enhanced. 

period Time Start of improved 

soil management 

Figure 4: Clean air and water start with 

soil organic matter

Apply practices that enhance soil organic matter 

• Diverse, high biomass crop rotations

• Cover crops

• Reduced tillage

• Rotational grazing

Organic matter dynamics change 

• Increased surface residue forms a physical barrier to wind 

and water erosion.

• Higher residue rotations and cover crops contribute more 

organic matter and nutrients to the soil.

• Less soil disturbance means lower organic matter losses.

Soil properties change 

• Surface structure becomes more stable and less prone to 

crusting and erosion.

• Water infiltration increases and runoff decreases when soil 

structure improves.

• Soil organic matter holds 10 to 1,000 times more water and 

nutrients than the same amount of soil minerals.

• Beneficial soil organisms become more numerous and active 

with diverse crop rotations and higher organic matter levels.

Air quality, water quality, and agricultural productivity improve 

• Dust, allergens, and pathogens in the air immediately decline. 

• Sediment and nutrient loads decline in surface water as soon as 

soil aggregation increases and runoff decreases. 

• Ground and surface water quality improve because better 

structure, infiltration, and biological activity make soil a 

more effective filter.

• Crops are better able to withstand drought when infiltration 

and water holding capacity increase.

• Organic matter may bind pesticides, making them less active. 

Soils managed for organic matter may suppress disease 

organisms, which could reduce pesticide needs.

• Crop health and vigor increase when soil biological activity 

and diversity increase.

• Wildlife habitat improves when residue management improves. 
What can you do? 

Go beyond T – Manage for C. Focus on management practices that 

build soil carbon and enhance soil function across the landscape. 

Practice standards important to organic matter management include: 

• Conservation Crop Rotation (328)

• Cover Crop (340)

• Residue Management–Mulch Till, No Till, Strip Till, Ridge Till 

(329A-C)

• Prescribed Grazing (528) when used to improve the health and vigor 

of pasture plant communities and to improve soil condition. 

In addition, appropriate irrigation technology may be important to 

increas-ing plant vigor and biomass production. 

Expect a transition period and learning curve associated with 

management changes. Soil biological and physical properties will 

improve before increased soil organic matter is noticeable. 

Avoid single-bullet solutions. No single practice works alone to 

enhance soil function, and no single set of practices works everywhere. 

Aim to improve soil organic matter and soil function, rather than to 

imple-ment a particular set of practices. 

Well-managed, continuous no till may be the most cost effective practice 

in many places, but even no till may not stand alone. No till should be 

com-bined with compaction prevention; a diverse, high-biomass 

rotation; and other locally relevant practices. In some areas, such as on 

wet and clayey soils, strip tillage or other variations are preferable. 

Protect the investment. In many parts of the country, every tillage 

event can reduce soil organic matter. Occasional tillage can destroy all 

of the organic matter gained during several years of no till. 

For more information about soil quality and soil organic matter, visit 

the NRCS Soil Quality Web site at http://soils.usda.gov/sqi. 

Produced by the USDA Natural Resources Conservation Service http://www.nrcs.usda.gov. 

The Natural Resources Conservation Service provides leadership in a partnership effort to help people conserve, maintain, 

and improve our natural resources and environment. 

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August 2003