Secondary Nutrients - Soil Health Nexus

What are secondary nutrients?

Photo Credit: https://www.agronomy.k-state.edu/documents/nutrient-management/nmrg-ppt-secondary-nutrients.pdf

Secondary nutrients are nutrients that slightly limit crop growth and are moderately required by plants. These nutrients are calcium (Ca), magnesium (Mg), and sulfur (S). Secondary nutrients are as significant as primary nutrients in plants, but they are needed in smaller quantities.

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Title	Source	Resource type and Date	Short Summary / Preview
Sulfur, Calcium and Magnesium	Kansas State University	Extension Training Manual Not Dated	This is a section from an extension handbook. This section is on sulfur, calcium, and magnesium requirements for common row crops.
Secondary Nutrients	Kansas State University	Presentation Not Dated	This is a Powerpoint slide set developed and used for extension training purposes. It contains information on sulfur, calcium, and magnesium with respect to the amounts needed for producing row crops.
Other Nutrients	SARE	Book Excerpt 2007	Although farmers understandably focus on nitrogen and phosphorus—because of the large quantities used and the potential for environmental problems—additional nutrient and soil chemical issues remain important.
Essential Elements for Plant Growth – Primary and Secondary Nutrients	University of Wisconsin	University Webpage Oct 1995	The ability of soils to supply secondary nutrients to plants indefinitely is is subject to the law of conservation of matter and is therefore dependent upon nutrient cycling. Continued crop removal of Ca, Mg, and S requires replentishment just as surely as primary nutrients, but most likely less frequently.

Sulfur

Title	Source	Resource type and Date	Short Summary / Preview
Sulfur for Minnesota Soils	University of Minnesota	Extension Webpage 2020	This is an in-depth publication of sulfur for Minnesota soils, which goes into detail about its availability to growing crops from different soil types and from non-harvested crop residues. This resource describes several sources of sulfur, describes removal of sulfur from the soil system, such as crop uptake, removal and leaching, and describes deficiency symptoms in crops, such as alfalfa and corn. Sufficiency levels of sulfur in the tissue of several crops are listed, soil test interpretation of sandy soils and response to sulfur from other soil types with different organic matter levels are given. Recommendations, methods of application and sources of sulfur fertilizer are provided.
Sulfur Deficiency	Purdue University	Extension Publication Jul 2017	This publication from Indiana first explains some of the reasons why we are seeing sulfur deficiency symptoms in crops in recent years. It describes how more sulfur is being removed in crops and how soil properties and crop management affect sulfur availability. It describes the relationship of soil testing and sulfate-sulfur trends over time, how to diagnose sulfur deficiency, and using tissue sampling with soil testing to determine sulfur deficiencies. Methods and fertilizer materials are listed and best management practices are discussed. Impact of sulfur containing fertilizers on soil pH is described.

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Source

Resource type and Date

Short Summary / Preview

Sulfur for Minnesota Soils

University of Minnesota

Extension Webpage

2020

This is an in-depth publication of sulfur for Minnesota soils, which goes into detail about its availability to growing crops from different soil types and from non-harvested crop residues. This resource describes several sources of sulfur, describes removal of sulfur from the soil system, such as crop uptake, removal and leaching, and describes deficiency symptoms in crops, such as alfalfa and corn. Sufficiency levels of sulfur in the tissue of several crops are listed, soil test interpretation of sandy soils and response to sulfur from other soil types with different organic matter levels are given. Recommendations, methods of application and sources of sulfur fertilizer are provided.

Sulfur Deficiency

Purdue University

Extension Publication

Jul 2017

This publication from Indiana first explains some of the reasons why we are seeing sulfur deficiency symptoms in crops in recent years. It describes how more sulfur is being removed in crops and how soil properties and crop management affect sulfur availability. It describes the relationship of soil testing and sulfate-sulfur trends over time, how to diagnose sulfur deficiency, and using tissue sampling with soil testing to determine sulfur deficiencies. Methods and fertilizer materials are listed and best management practices are discussed. Impact of sulfur containing fertilizers on soil pH is described.

Calcium and Magnesium Ratios

Title	Source	Resource type and Date	Short Summary / Preview
Calcium and magnesium: the secondary cousins	University of Minnesota	Lesson Not Dated	This lesson focuses on the importance of Ca and Mg in Minnesota soils and their role in plant nutrition. Frequently, Ca and Mg are grouped with potassium (K) and referred to as the basic cations.
Soil calcium to magnesium ratios— Should you be concerned?	University of Wisconsin	Extension Fact Sheet Nov 1993	While some sales people and scientists have claimed that there is an “ideal” soil calcium to magnesium ratio (Ca:Mg), and that Wisconsin soils contain too much magnesium for the amount of calcium present, research in Wisconsin shows this is not true.
Soil calcium:magnesium ratios	Iowa State University	Extension Webpage Apr 2003	All soils contain calcium ions (Ca²⁺) and magnesium (Mg²⁺) cations (positively charged ions) attracted to the negative exchange sites on clays and organic matter (cation exchange complex of the soil). The amount and relative proportion usually reflect the soil’s parent materials.
Soil calcium-to-magnesium ratios should not concern most farmers	Michigan State University	Extension Blog Post Nov 2016	If soil calcium and magnesium levels are adequate and soil pH is acceptable, variations in the calcium-to-magnesium ratio between 2 and 8 have been shown to have no influence on crop yield.

Magnesium

Title	Source	Resource type and Date	Short Summary / Preview
Magnesium for crop production	University of Minnesota	Extension Webpage 2016	Although magnesium (Mg) is an essential element for plant growth, its use in a fertilizer program receives only minor emphasis in Minnesota.

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Short Summary / Preview

Magnesium for crop production

University of Minnesota

Extension Webpage

2016

Although magnesium (Mg) is an essential element for plant growth, its use in a fertilizer program receives only minor emphasis in Minnesota.

Calcium

Title	Source	Resource type and Date	Short Summary / Preview
Calculating Cation Exchange Capacity, Base Saturation, and Calcium Saturation	The Ohio State University	Extension Webpage Aug 2019	The purpose of this fact sheet is to define soil cation exchange capacity, base saturation and calcium saturation, and demonstrate how these values are calculated in soil test reports.
Properties of Gypsum That Provide Benefits for Agricultural Uses	The Ohio State University	Chapter 2 of Extension Publication 2011	This publication discusses how sulfur deficiencies are more common today and gypsum can be a good source of sulfur, especially for alfalfa, increasing yields. It explains how gypsum is a good source of calcium and this can improve quality of horticultural crops and enhance peanut production. It explains that gypsum as a soil amendment can improve soil physical properties, like overcoming the dispersion effects of sodium and magnesium and improving water infiltration.
Gypsum for Agricultural Use in Ohio—Sources and Quality of Available Products	The Ohio State University	Extension Publication Aug 2005	This article summarizes gypsum’s role as a soil amendment and lists different sources and mineral compositions for gypsum. The physical properties, price, plant nutrient content and trace mineral content of different gypsum materials are also listed.

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Source

Resource type and Date

Short Summary / Preview

Calculating Cation Exchange Capacity, Base Saturation, and Calcium Saturation

The Ohio State University

Extension Webpage

Aug 2019

The purpose of this fact sheet is to define soil cation exchange capacity, base saturation and calcium saturation, and demonstrate how these values are calculated in soil test reports.

Properties of Gypsum That Provide Benefits for Agricultural Uses

The Ohio State University

Chapter 2 of Extension Publication

2011

This publication discusses how sulfur deficiencies are more common today and gypsum can be a good source of sulfur, especially for alfalfa, increasing yields. It explains how gypsum is a good source of calcium and this can improve quality of horticultural crops and enhance peanut production. It explains that gypsum as a soil amendment can improve soil physical properties, like overcoming the dispersion effects of sodium and magnesium and improving water infiltration.

Gypsum for Agricultural Use in Ohio—Sources and Quality of Available Products

The Ohio State University

Extension Publication

Aug 2005

This article summarizes gypsum’s role as a soil amendment and lists different sources and mineral compositions for gypsum. The physical properties, price, plant nutrient content and trace mineral content of different gypsum materials are also listed.

Title	Source	Resource type and date	Short Summary
Primary and secondary minerals	University of California, Davis	University Webpage Not Dated	For sedimentary and metamorphic rocks, the elemental and mineralogical composition is determined by the chemical and mineralogical composition of the sediments and rocks from which they form.
Macro and secondary nutrients – soil diagnostics	Ontario Ministry of Agriculture	Governmental Webpage Mar 2009	From the Ontario Ministry of Agriculture, Food and Rural Affairs this article summarizes the three types of macronutrients and three secondary nutrients (including sulfur) which crops need including how to identify sulfur deficiency and potential sources of sulfur.
Secondary Macronutrients: Cycling, Testing and Fertilizer Recommendations	Montana State University	Lesson Jul 2002	This module is the sixth in a series of Extension materials designed to provide Extension agents, Certified Crop Advisers (CCAs), consultants, and producers with pertinent information on nutrient management issues.
Secondary Plant Nutrients: Calcium (Ca), Magnesium (Mg), and Sulfur (S)	University of California	Extension Fact Sheet not dated	This article (Part 3) discusses the use of soil tests to evaluate levels of the secondary nutrients calcium (Ca), Magnesium (Mg), and sulfur (S) in orchard soils.
Secondary Plant Nutrients: Calcium, Magnesium, and Sulfur	Mississippi State University	Extension Publication Jul 2019	A summary of the three principal secondary plant nutrients, how and where to look for secondary nutrient deficiencies and where to find reliable sources of sulfur should soil require it.
Soil Nutrient Management For Forages: Phosphorus, Potassium, Sulphur, and Micronutrients	Montana State University	Extension Publication 2018	Improvements in forage production have the potential to increase income and significantly reduce livestock production costs. Soil fertility is important for forage production, stand health/longevity, and forage quality.
Calcium and Magnesium For Mississippi Crops	University of Mississippi	Extension Webpage Feb 2011	Calcium (Ca) and (Mg) magnesium are positively charged secondary nutrients. They are generally adequate in most Mississippi soils with favorable pH and organic matter levels.

Title	Source	Resource type and Date	Short Summary / Preview
Patterns of Soil Calcium and Aluminum Across the Conterminous United States (Chapter 9 of Forest Health Monitoring: 2008 National Technical Report)	U.S. Department of Agriculture Forest Service	Book Chapter Jun 2012	Calcium (Ca) is a cation—positive ion—used by plants to build cell walls. It is also involved in root and leaf development and the activation of plant enzymes

Title

Source

Resource type and Date

Short Summary / Preview

Patterns of Soil Calcium and Aluminum Across the Conterminous United States (Chapter 9 of Forest Health Monitoring: 2008 National Technical Report)

U.S. Department of Agriculture Forest Service

Book Chapter

Jun 2012

Calcium (Ca) is a cation—positive ion—used by plants to build cell walls. It is also involved in root and leaf development and the activation of plant enzymes

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