pH - Soil Health Nexus

What is pH?

Photo Credit: https://extension2.missouri.edu/g9102

Soil pH is an indicator of how acidic, neutral or alkaline (basic) a soil is, based on the hydrogen ion concentration – where pH is reported as a negative logarithm and ranges from 0-14. Common classes of soil pH include: extremely acid (3.5-4.4), extremely to slightly acid (4.5 to 6.5), neutral (6.6 to 7.3), and slightly to very alkaline (7.4 to 9.0). A pH range of 6.0 to 7.0 favors growth of most crops, although some crops have specific acid or alkaline soil requirements to be productive. Understanding soil pH will help to understand the influences of soil chemistry and biology and how nutrient availability and soil organic carbon are impacted. To guide you in selection of an article, the Soil Nexus team suggests that you choose an article based on soil types of interest, which are often typical of a geographical region.

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Regional Educator ResourcesOther Educator ResourcesTechnical Resources

Title	Source	Resource type and Date	Short Summary / Preview
Liming Missouri Soils	University of Missouri	Extension Webpage Feb 2000	Just about everything people and nature do to the soil tends to create acidity. Liming acid soils increases yields and provides a number of other soil health benefits.
Missouri Limestone Quality: What Is ENM?	University of Missouri	Extension Webpage Oct 1993	The effectiveness of limestone refers to its ability to neutralize soil acidity. To measure the ability to reduce acidity, a rating system was developed. This rating system is called effective neutralizing material (ENM).
The Meaning and Importance of Soil pH	Iowa State University	Extension Blog Post May 2002	Garden soils are often described as acidic (sour) or alkaline (sweet). The relative acidity or alkalinity of soil is indicated by its pH.
Soil pH	North Dakota State University	Extension Webpage Not Dated	The pH of a soil influences nutrient availability, toxicity, microbial populations, and activity of certain pesticides. Soils with a pH less than 7 referred to as acidic and pH levels greater than 7 are considered basic or alkaline.
Soil Acidity	SARE	Governmental / Extension Webpage Not Dated	Several problems may cause poor growth of acid-sensitive plants in low pH soils.
Soil pH	Soilquality.org – NRCS & others	Webpage 2011	Soil pH affects the soil’s physical, chemical, and biological properties and processes, as well as plant growth. The nutrition, growth, and yields of most crops decrease where pH is low and increase as pH rises to an optimum level.
Soil phosphorus availability and lime: more than just pH?	Soil Science Society of America	Researcher Blog Post Not Dated	One influence on phosphorus availability is the soil’s pH level. If soils are too acidic, phosphorus reacts with iron and aluminum. That makes it unavailable to plants. But if soils are too alkaline, phosphorus reacts with calcium and also becomes inaccessible.
Soil Quality Indicators: Chemical Indicators and Soil Functions	USDA	NRCS Fact Sheet Feb 2015	Fact Sheet. Different chemical indicators widely used are related to the respective basic functions they measure.
Soil Quality Indicators: Soil pH	USDA	NRCS Fact Sheet Apr 2011	Fact Sheet. Soil pH generally refers to the degree of soil acidity or alkalinity.
Soil pH	USDA – NRCS	NRCS Fact Sheet and Instructor Guide Not Dated	Soil pH is a measure of soil acidity or alkalinity. It is an important indicator of soil health. It affects crop yields, crop suitability, plant nutrient availability, and soil micro-organism activity which influence key soil processes. Soil pH can be managed by measures such as applying the proper amount of nitrogen fertilizer, liming, and cropping practices that improve soil organic matter and overall soil health.
Commercial Greenhouse Production: pH and Electrical Conductivity Measurements in Soilless Substrates	Purdue University	Extension Publication Jun 2009	Monitoring the pH and electrical conductivity (EC) of growing substrates is a way to correct issues before they become problems that damage crops. This publication recommends best practices for establishing a pH and EC testing program in soilless substrates, and outlines the procedures, advantages, and disadvantages of three accepted methods for testing media solutions.
Some basic concepts of liming	Kansas State University	Extension Blog Jul 2014	This short article provides an overview of when liming is needed and for which field crops this is especially important.
Soil pH and Liming	Kansas State University	Extension Training Manual Not Dated	This is a section from an extension handbook. This section is on pH and liming requirements for common row crops.
Lime and soil pH	Iowa State University	List of University Resources Not Dated	This is a list of extension publications and conference proceedings on lime and soil pH. The breadth of topics covered is from basic to very specific on this topic

Title	Source	Resource type and date	Short Summary
Soil pH and Organic Matter	Montana State University	Extension Fact Sheet Mar 2017	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.
Soil pH: What it Means	State University of New York	Webpage Not Dated	From the SUNY College of Environmental Science and Forestry: Soil pH or soil reaction is an indication of the acidity or alkalinity of soil and is measured in pH units. Soil pH is defined as the negative logarithm of the hydrogen ion concentration. The pH scale goes from 0 to 14 with pH 7 as the neutral point.
Soil pH – The Master Variable	University of Connecticut	Extension Blog Post Dec 2018	Monitoring your soil pH is essential to ensure that it is falling within the range best suited for the vegetation you are growing. The Standard Nutrient Analysis performed at our lab gives you a pH value, a buffer pH value, a lime/sulfur recommendation, available micro & macro nutrient levels, and a fertilizer recommendation.
Soil Acidity, pH, and Liming	UMass Amherst	University Webpage Not Dated	One of the most important aspects of nutrient management is maintaining proper soil pH, a measure of soil acidity.
Soil Acidity: It’s not just pH	Washington State University	Presentation Not Dated	General information on soil acidity.
Changing the pH of your soil	Clemson University	Extension Webpage Oct 2012	To raise the pH of soil, the common practice is to apply a material that contains some form of lime. Two materials commonly used for lowering the soil pH are aluminum sulfate and sulfur.
Soil Acidity and pH	Cornell University	Presentation Not Dated	General information on soil acidity.
Water and Soil Characterization – pH and Electrical Conductivity	Montana State University	University Webpage Not Dated	pH is a measure of the acidity of the water or soil based on its hydrogen ion concentration and is mathematically defined as the negative logarithm of the hydrogen ion concentration.
Soil Acidity and Liming: Basic Information for Farmers and Gardeners	NC State Extension	Extension Webpage Dec 2018	Nearly all North Carolina soils are naturally acidic and need lime, which neutralizes the acidity, for optimum growth of crops, forages, turf, trees, and many ornamentals. Even though most of these soils have been limed in the past, periodic additions of lime based on soil tests are still needed.
Soil Acidity and Liming for Agricultural Soils	NC State Extension	Extension Webpage Mar 2017	Nearly all North Carolina soils are naturally acidic and need lime, which neutralizes the acidity, for optimum growth of crops, forages, turf, trees, and many ornamentals.
Soil Acidity and Aglime	Penn State	Extension Webpage Nov 2014	Soil acidity is among the important environmental factors which can influence plant growth, and can seriously limit crop production. The soil pH is a general indicator of whether aglime is needed to reduce the acidity.
Soil pH: What it Means	State University of New York	University Webpage Not Dated	As the amount of hydrogen ions in the soil increases the soil pH decreases thus becoming more acidic.

Title	Source	Resource type and Date	Short Summary
Agronomic Services — Mehlich Buffer Acidity	North Carolina Department of Agriculture and Human Services	Governmental Webpage Apr 2013	The Mehlich buffer method for determining exchangeable acidity (Ac) was developed under the premise that an increase or decrease in exchangeable acidity can be quantified by measuring the corresponding increase or decrease in the pH of a buffered reagent.
Soil pH	Michigan State University, LTER	Extension/Research Protocol Not Dated	Protocol to measure soil pH. Soil pH is a measure of the hydrogen ion activity in soil solution; high hydrogen activity (low pH) is an index of soil acidity which can affect nutrient availability and plant growth.
Exchangeable Ions, pH, and Cation Exchange Capacity (Chapter 6 of Standard Soil Methods for Long-term Ecological Research)	Oxford University Press	Book chapter 1999	This book chapter provides the definition of Exchangeable Ions, pH and Cation Exchange Capacity. It also lists materials needed and describes the procedure, calculations and special considerations in determining these soil properties.

Title

Source

Resource type and Date

Short Summary

Agronomic Services — Mehlich Buffer Acidity

North Carolina Department of Agriculture and Human Services

Governmental Webpage

Apr 2013

The Mehlich buffer method for determining exchangeable acidity (Ac) was developed under the premise that an increase or decrease in exchangeable acidity can be quantified by measuring the corresponding increase or decrease in the pH of a buffered reagent.

Soil pH

Michigan State University, LTER

Extension/Research Protocol

Not Dated

Protocol to measure soil pH. Soil pH is a measure of the hydrogen ion activity in soil solution; high hydrogen activity (low pH) is an index of soil acidity which can affect nutrient availability and plant growth.

Exchangeable Ions, pH, and Cation Exchange Capacity (Chapter 6 of Standard Soil Methods for Long-term Ecological Research)

Oxford University Press

Book chapter

1999

This book chapter provides the definition of Exchangeable Ions, pH and Cation Exchange Capacity. It also lists materials needed and describes the procedure, calculations and special considerations in determining these soil properties.

This page reviewed by Liz Schultheis, DeAnn Presley, Mike Kucera, Gary Lesoing, Paul Gross, Anna Cates, Kenny Eck, Walt Sell, Christina Curell, and Vicki Morrone.

Technical review: March 18, 2020