Aggregation and Aggregate Stability

What is Aggregation? Aggregate Stability?

This picture was taken after a slump demonstration conducted on two soils comparing aggregation between no-till and conventional tillage systems. Photo Credit: Joe Rorick, Purdue University

Soil aggregation is described as how well soil particles are bond together through fungi binding threads based on soil composition and texture. Aggregate Stability is the measured ability of a soil to hold together and maintain structure despite disruptive forces such as raindrops; water and/or wind erosion impacts; shrinking and swelling conditions or tillage.

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Regional Educator ResourcesOther Educator ResourcesTechnical Resources

Title	Source	Resource type and date	Short Summary
Rainfall simulator – soil health demonstration	Michigan State University	Video Demonstration Sep 2019	Paul Gross and Dean Baas, from Michigan State University Extension, give a rainfall simulator demonstration. The demonstration covers soil health topics such as runoff, water holding capacity, and aggregate stability.
What are soil aggregates?	Soil Science Society of America	Extension Webpage Jul 2019	Aggregate formation is a complex process. Soil aggregates are formed through physical, chemical and biological activity below ground. They are even influenced by human factors, like tilling, walking on the surface, or even how you fertilize your garden.
Soil Aggregate Stability – a soil health physical indicator	Ohio State University	Extension Webpage Feb 2018	Soil aggregate stability is an important physical indicator of soil health, which protects organic matter accumulation, improves soil porosity, drainage and water availability for plants, decreases soil compaction, supports biological activity, and nutrient cycling in the soil.
Soil Quality Indicators: Aggregate Stability	USDA	NRCS Factsheet Jun 2008	Soil aggregates are groups of soil particles that bind to each other more strongly than to adjacent particles. Aggregate stability refers to the ability of soil aggregates to resist disintegration when disruptive forces associated with tillage and water or wind erosion are applied.
Soil Health Spotlight: Soil structure and aggregation	Kansas State University	Web Article Feb 2020	A basic discussion of soil structure and aggregation.
Aggregate Stability	Soilquality.org – NRCS & others	Webpage Sep 2011	Changes in aggregate stability may serve as early indicators of recovery or degradation of soils. Aggregate stability is an indicator of organic matter content, biological activity, and nutrient cycling in soil.
Soil Quality Indicators: Slaking	USDA	NRCS Factsheet Jun 2008	Slaking is the breakdown of large, air-dry soil aggregates (>2-5 mm) into smaller sized microaggregates (<0.25 mm) when they are suddenly immersed in water. Slaking occurs when aggregates are not strong enough to withstand internal stresses caused by rapid water uptake.
Slaking	Soilquality.org – NRCS & others	Extension Webpage Sep 2011	Slaking indicates the stability of soil aggregates, resistance to erosion and suggests how well soil can maintain its structure to provide water and air for plants and soil biota when it is rapidly wetted.
Rangeland Soil Quality—Aggregate Stability	USDA	NRCS Factsheet May 2001	Soil aggregates are soil particles that are bound more closely to each other than to surrounding particles. The stability of these aggregates is critical to soil erosion, water availability, and root growth.
Soil Health 101	Soil Health NEXUS	Extension Webpage Jan 2017	The soil structure is made up of the soil profile, bulk density, and aggregates
Soil aggregation	North Dakota State University	Extension Webpage 2014	Soil aggregation is part of soil’s structure and function and a good indicator of soil health.
Soil Health Nexus Demonstration How-To: Slump Test	Soil Health NEXUS	How-to Video May 2019	Techniques to measure soil structure and aggregation. The more aggregate stability you have, the more stable your soil. Prevents erosion.
Soil Physical Properties Fact Sheet	North Dakota State University	Extension Factsheet Not Dated	Soil physical properties affect the behavior of soil and the functional processes required to meet environmental and human needs.
On-Farm Soil Monitoring for Water Resource Protection: Farm Assessment for Water Resource Protection	Purdue University	Extension Publication Dec 2003	These five on-farm soil monitoring methods are intended to replace analytical soil tests. These monitoring methods and indicators include: Water infiltration rate, earthworm count, soil aggregate stability, penetration compaction, and plant and crop residue cover.
Youth Soil Quality Lessons and Videos – Components and Physical Properties of Soil	University of Nebraska	Extension Webpage Not Dated	The quality of soil depends upon a variety of factors. NRCS has developed Soil Quality Kit Guides, fact sheets and materials for teachers to integrate into their soils curriculum. In addition, a curriculum has been developed to use in the classroom. These materials were created with funds provided by the Nebraska Environmental Trust. YouTube videos supplement these curricula as well.
Soil Stability	Purdue Soil Health Education Webpage	Video Sep 2017	Short basic educational video on soil stability using the slake test by Dr. John Graveel, Purdue University.
How to Understand and Interpret Soil Health Tests	Purdue University	Extension Publication Jun 2018	Purdue and CCSI did some research using some commercial soil health tests. This document describes some descriptions and guidelines that came out of doing that work.
Soil Water and Aggregation	SARE	Governmental / Extension Webpage Not Dated	Processes like erosion, soil settling, and compaction are affected by soil moisture conditions, and in turn affect soil hardness and the stability of aggregates.
Soil Quality Demonstrations and Procedures	USDA-ARS	Lesson Plans Jan 2011	Demonstrations and procedures including all of the following and more: Soil as a Precious Resource, Rainfall Simulator – Soil Erosion, Soil Macroaggregate Scale Model, Dry sieving to collect soil aggregates, Wet Sieving to measure water stable aggregation (WSA), Soil Aggregates – Edible Stability
The Biology of Soil Compaction	Ohio State University	Extension Factsheet Dec 2009	Soil compaction is a common and constant problem on most farms that till the soil. Soil compaction is reduced by the formation of macroaggregates in the soil. Microaggregate soil particles (clay, silt, particulate organic matter) are held together by humus or old organic matter residues and are resistant to decomposition.

Title	Source	Resource type and date	Short Summary
Improving Aggregate Stability	Cornell University	Extension Factsheet 2016	Soil texture, climate, and the health, quantity, and diversity of soil organisms affect aggregate stability. Field management, including tillage operations, addition of organic amendments, and planting and harvesting methods, can impact both aggregate size distribution and stability.
Soil Quality Information	Penn State	Extension Webpage Aug 2012	Healthy soils yield healthy crops, But what is healthy soil and how do we achieve it?
Assessing soil aggregate stability	Murray Catchment Management Authority	Video by Australian Government Organization May 2012	Video on how to measure. The aggregate stability of the soil is tested by observing whether slaking or dispersion occurs after the aggregate is added to water. Slaking vs. dispersion. Slaking is the breakdown of an aggregate of soil into much smaller aggregates on wetting, and is caused by the swelling of clay and the sudden release of trapped gases. Dispersion is the separation of soil particles from aggregates so the structure completely disintegrates into individual particles.
Soil aggregate stability	Department of Primary Industries & Regional Development, Australia	Governmental Webpage Jan 2018	Soil aggregate stability refers to the ability for a soil to regulate the movement and storage of air and water throughout the soil profile which is determined by the soil make up of sand, silt and clay particles. The more stable the soils aggregates the more productive the soil.

Title	Source	Resource type and date	Short Summary
Soil Aggregate Stability: A Review	Journal of Sustainable Agriculture	Peer-reviewed Publication Nov 1998	This paper reviews the different methods of measurement of soil aggregate stability used in the literature, paying attention to the conditions of sample collection in the field and sample preparation and treatments in the laboratory.
Evaluation of methods for determining soil aggregate stability	Soil and Tillage Research	Peer-reviewed Publication Apr 2017	Different methods for measuring aggregate stability are poorly correlated. Choice of methodology should mimic breakdown of field aggregates.

Title

Source

Resource type and date

Short Summary

Soil Aggregate Stability: A Review

Journal of Sustainable Agriculture

Peer-reviewed Publication

Nov 1998

This paper reviews the different methods of measurement of soil aggregate stability used in the literature, paying attention to the conditions of sample collection in the field and sample preparation and treatments in the laboratory.

Evaluation of methods for determining soil aggregate stability

Soil and Tillage Research

Peer-reviewed Publication

Apr 2017

Different methods for measuring aggregate stability are poorly correlated. Choice of methodology should mimic breakdown of field aggregates.

This page reviewed by Liz Schultheis, Rick Koelsch, Anna Cates, Joe Rorick, Walt Sell, and Chryseis Modderman.

Last reviewed 10/1/19