Soil Calcium and Magnesium Levels

decrease font size  Resize text   increase font size       Printer-friendly version of this article Printer-friendly version of this article

Source: Dorivar Ruiz-Diaz, Nutrient Management Specialist, Kansas State University

Is it important to have the proper ratio of calcium (Ca) and magnesium (Mg) in the soil? Producers may ask this question as they have their soil tested for nutrient levels in the summer before wheat planting begins. This question may also arise at the moment of lime purchase, which can be an important source of Ca and Mg.

Calcium and Mg are plant-essential nutrients. All soils contain Ca and Mg in the form of cations (positively charged ions, Ca++ and Mg++) that attach to the soil clay and organic matter; these are also the forms taken up by crops. The relative proportion of these elements, as well as the total amount in the soil, depends mainly on the soil parent material. In Kansas soils, the levels of Ca and Mg are typically high and crop deficiencies are rare.

Soils typically have higher Ca levels than Mg. Table 1 gives the amount and ratios of Ca and Mg for some soils in Kansas. Both nutrients are present in large quantities. Unusual cases of Ca or Mg deficiencies may be found in areas of very sandy soils. 

Table 1. Calcium, magnesium, and Ca:Mg ratio for several Kansas soils.

Soil

Ca

Mg

Ca:Mg ratio

 

- - cmol kg-1 - - -

 

Canadian-Waldeck

42

11

3.7

Carwile

22

4

5.2

Chase

198

30

6.7

Crete

111

29

3.8

Harney

202

15

13.2

Harney-Uly

200

12

16.1

Keith

127

38

3.3

Las

176

37

4.8

McCook

35

8

4.5

Onawa

163

28

5.8

Ortello

19

6

3.3

Parsons

80

23

3.5

Tully

158

38

4.2

Why would the ratio of Ca to Mg be important? The concept of an optimum Ca:Mg ratio started in the 1940s under the "basic cation saturation ratio" theory. The theory is that an "ideal soil" will have a balanced ratio of Ca, Mg and potassium (K). According to this theory, fertilization should be based on the soil's needs rather than crop’s needs — focusing on the ratio of crop nutrients present in the soil. This concept of an ideal Ca:Mg ratio has been debated by agronomists over the years. The suggested ideal ratio according to the theory is between 3.5 and 6.0, but this has never proven to be of significance.

There is very little research evidence to support any effect, either positive or negative, of the soil Ca:Mg ratio on crop production and yield. What research studies have been conducted in the laboratory and in the field show no effect of Ca:Mg ratio on crop yield. Despite this, the promotion of the ratio concept persists today. Furthermore, the initial work that derived this concept did not differentiate between crop response (alfalfa) due to the change in Ca:Mg ratio and the improvement in soil pH from lime application. It is reasonable to conclude that crop response can be expected from changes in soil pH rather than any change in the ratio of Ca:Mg.

One example of research conducted on this topic over the years is shown in Table 2. In that experiment, McLean and coworkers demonstrated the lack of relationship between Ca:Mg ratio and crop yield for several crops. The range of Ca:Mg ratios observed for the highest yields were not different from those observed for the lowest yields. The conclusion from that study was that to achieve maximum crop yield, attention should center on providing sufficient levels of these nutrients rather than attempting to find an adequate ratio. Therefore when these nutrients are present in optimum levels for plant growth, the relative ratio in the soil seems irrelevant.

Table 2. Ratio of Ca:Mg for five crop-years comparing the highest and lower yields obtained

 

Corn

Corn

Soybean

Wheat

Alfalfa

Alfalfa

Yield level

   - - - - - - - - - - - - - - - - - - - - - - Ca:Mg ratio - - - - - - - - - - - - - - - - - - - - - -

Highest five

5.7 - 26.8

5.7 - 14.2

5.7 - 14.9

5.7 - 14.0

5.7 - 26.8

6.8 - 26.8

Lowest five

5.8 - 21.5

5.0 - 16.1

2.3 - 16.1

6.8 - 21.5

8.2 - 21.5

5.7 - 21.5

Adapted from: McLean, E.O., R.C. Hartwig, D.J. Eckert, and G.B. Triplett. 1983. Basic cation saturation ratios as a basis for fertilizing and liming agronomic crops. II. Field studies. Agronomy Journal 75: 635-639.

 
In conclusion, trying to manage the ratio of Ca:Mg should not be used for a nutrient application or liming program. The center of attention should be to ensure that levels of Ca and Mg in the soil will not limit optimum plant growth. The relative concentration of Ca and Mg in commercial ag lime can be highly variable, and application should be based on the effective calcium carbonate (ECC) to achieve a target soil pH.


Buyers Guide

Doyle Equipment Manufacturing Co.
Doyle Equipment Manufacturing prides themselves as being “The King of the Rotary’s” with their Direct Drive Rotary Blend Systems. With numerous setup possibilities and sizes, ranging from a  more...
A.J. Sackett Sons & Company
Sackett Blend Towers feature the H.I.M, High Intensity Mixer, the next generation of blending and coating technology which supports Precision Fertilizer Blending®. Its unique design allows  more...
R&R Manufacturing Inc.
The R&R Minuteman Blend System is the original proven performer. Fast, precise blending with a compact foot print. Significantly lower horsepower requirement. Low inload height with large  more...
Junge Control Inc.
Junge Control Inc. creates state-of-the-art product blending and measuring solutions that allow you to totally maximize operating efficiency with amazing accuracy and repeatability, superior  more...
Yargus Manufacturing
The flagship blending system for the Layco product line is the fully automated Layco DW System™. The advanced technology of the Layco DW (Declining Weight) system results in a blending  more...
Yargus Manufacturing
The LAYCOTE™ Automated Coating System provides a new level of coating accuracy for a stand-alone coating system or for coating (impregnating) in an automated blending system. The unique  more...
John Deere
The DN345 Drawn Dry Spreader can carry more than 12 tons of fertilizer and 17.5 tons of lime. Designed to operate at field speeds up to 20 MPH with full loads and the G4 spreader uniformly  more...
Force Unlimited
The Pro-Force is a multi-purpose spreader with a wider apron and steeper sides. Our Pro-Force has the most aggressive 30” spinner on the market, and is capable of spreading higher rates of  more...
BBI Spreaders
MagnaSpread 2 & MagnaSpread 3 — With BBI’s patented multi-bin technology, these spreaders operate multiple hoppers guided by independent, variable-rate technology. These models are built on  more...

Related Articles



Comments (0) Leave a comment 

Name
e-Mail (required)
Location

Comment:

characters left


Fertilizer Conveying Systems

Waconia Manufacturing routinely designs receiving systems for volume requirements from 60 to 1,500 TPH. All receiving systems are fabricated with ... Read More

View all Products in this segment

View All Buyers Guides

Feedback Form
Feedback Form