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Cations in Ecuadorian tropical soils: different extraction methods and interpretation of the analysis

Dr. Bernd Ditschar

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Introduction

- Calcium, Magnesium and Potassium as cations are fixed on organic matter and clay particles

- This fraction is exchangeable and always in balance with nutrients in the soil solution

- Soil analysis should analyze these two fractions –concentration in the soil solution and buffer capacity

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Introduction

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- Weak extractants such as water or sodium bicarbonate reflect mainly the concentration in the soil solution, whereas strong extractants primarily indicate the capacity of the soil to supply nutrients to the soil solution (buffer capacity); Marschner and Rengel(2012)

- strong extractants measure additional cations from the soil => cations which are not interchangeable (e.g. in the case of Mg and Ca free carbonates)

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CEC = Adsorption and desorption of cations

Two groups:

Acid forming group Basic-forming group

H+ and Al3+ Mg2+, Ca2+, K+ and Na+

IntroductionK+S KALI GmbH

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- Information from soil testing is a guideline for fertilizer recommendations

- there are two methods:

a) SLAN – sufficient level of available nutrients (optimum level in the soil, it is plant specific)

b) BCSR – mineral balancing in soils (Albrecht papers)

Cation-Relation: Why it is important in Latin America?

Cation relation in soilCa 60Mg 30K 10

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Ancupa (2013) reports an optimal cation relation in soils specific for oil palm

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„Amarillamiento secamiento“ in oil palm

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60:30:10 80:15:5

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Source: ancupa 2013

„Yellowing“ and „Drying“ of leaves in oil palm

Ca:Mg:K

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Mg Ca K Totalmg/ kg 163 1614 322 2099

Medio M-A Alto

Soil analysis:

Example from Ecuador (Olsen „Modified“)

7,76% 76,9% 15,3%

Interpretation (according to ancupa, Ecuador):

Strong Mg-deficiency due to high Ca content!

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organic matter 9.1%, sand 48%, lime 43%, clay 9%

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Example from Ecuador

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Soil sampling andMg-deficiency

in Oil plamSource: own data

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Hypothesis

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It might be that there is a specific cation ratio which is favorable to plants, especially for oil palm.

If the extraction of cations from the exchange complex depends of the “strongness” of the extractant the total amount of Ca, Mg an K differs on the method used.

And

Are the extraction methods comparable?

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Methods for soil analyses in Latin America

102012-12, CS-Sp

In Ecuador the “Olsen modified” method is the standard method for Ca, Mg and K but it is originally a method for phosphorous

Different methods for soil testing in Latin America:Extractant Extraction

timeDissolution

Water 1 h 1:5NaCl 0.1M 1 h 1:10KCl 0.1M 1 h 1:10CaCl2 1 h 1:10Mehlich-3 15` 1:10Ammonium-Acetate 1M 1 h 1:20Sodium-Acetate 1M 1 h 1:20Olsen Modified (Olsen + EDTA 0.05M) 30` 1:20

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Ecuadorian Soils analyzed

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Soil Organic Matter (%)

Sand(%)

Lime(%)

Clay(%)

Franca arcillosa

6.9 28 32 40

Arcilla 5.7 23 30 47Franca arenosa

9.1 48 43 9

Franca 7.7 40 44 16Franca arenosa

10.8 45 46 9

Soil sampling: 13.8.2014 in Ecuador at different oil palm plantations

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Soil sample 3

12Date (YYMMDD), title, author/sign

0

500

1000

1500

2000

A B C D E F

Ca

(mg

kg-1

)

0

50

100

150

200

250

A B C D E FM

g (m

g kg

-1)

Soil Organic Matter (%)

Sand(%)

Lime(%)

Clay(%)

Franca arenosa 9.1 48 43 9

0

100

200

300

400

A B C D E F

K (m

g kg

-1)

A (NaCl); B (KCl/CaCl2), C (Mehlich-3), D (Ammonium-Acetate), E (Sodium-Acetate) and F (Olsen Modified)

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Soil sample 5

13Date (YYMMDD), title, author/sign

0

200

400

600

800

A B C D E F

Ca

(mg

kg-1

)

0

50

100

150

A B C D E FM

g (m

g kg

-1)

Soil Organic Matter (%)

Sand(%)

Lime(%)

Clay(%)

Franca arenosa 10.8 45 46 9

0

10

20

30

40

50

A B C D E F

K (m

g kg

-1)

A (NaCl); B (KCl/CaCl2), C (Mehlich-3), D (Ammonium-Acetate), E (Sodium-Acetate) and F (Olsen Modified)

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Conclusion of different methods used

14Date (YYMMDD), title, author/sign

- The total amount of interchangeable cations of Ca, Mg and K (mg kg-1) found by each method are highly different

- Ammonium-Acetate showed the highest Mg levels in both soils; similar trend was found by the other methods

- Important is the interpretation of the analysis to give soil nutrient levels

But

Are the different methods comparable?

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Comparison of different soil extraction methods

15Date (YYMMDD), title, author/sign

0100200300400500600700

0 200 400 600 800 1000

Mg-

Meh

lich-

3

Mg-KCl

0200400600800

10001200

0 200 400 600 800 1000

Mg-

Meh

lich-

3

Mg-Olsen

0

200

400

600

800

1000

0 200 400 600 800 1000

Mg-

Meh

lich-

3

Mg-Ammonium-Acetate

0200400600800

10001200

0 200 400 600 800 1000Mg-

Am

mon

ium

acet

ate

Mg-Olsen

r2 = 0,9979 r2 = 0,9975

r2 = 0,9964 r2 = 0,9992

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Mg2+

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Comparison of different soil extraction methods

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KCl NaCl Mehlich-3 Ammonium-Acetate

Sodium-Acetate

Olsen"Modified"

KCl x

NaCl 0.9917 x

Mehlich-3 0.9979 0.9839 x

Ammonium-Acetate 0.9910 0.9681 0.9964 x

Sodiumacetate 0.9944 0.9756 0.9989 0.9990 x

Olsen Modified 0.9935 0.9713 0.9975 0.9992 0.9988 x

Mg2+

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Comparison of different soil extraction methods

17Date (YYMMDD), title, author/sign

0

500

1000

1500

2000

2500

0 400 800 1200 1600

Ca-

Meh

lich-

3

Ca-KCl/CaCl

r2 = 0,9666

0

500

1000

1500

2000

2500

0 700 1400 2100 2800

Ca-

Meh

lich-

3

Ca-Olsen

r2 = 0,9525

0

800

1600

2400

0 800 1600 2400

Ca-

Meh

lich-

3

Ca-Ammoniumacetate

r2 = 0,9983

0

500

1000

1500

2000

2500

0 800 1600 2400 3200Ca-

Am

mon

ium

acet

ate

Ca-Olsen

r2 = 0,9390

Ca2+

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Comparison of different soil extraction methods

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KCl NaCl Mehlich-3 Ammonium-Acetate

Sodium-Acetate

Olsen „Modified“

KCl x

NaCl 0.9379 x

Mehlich-3 0.9666 0.9430 x

Ammonium-Acetate 0.9097 0.9407 0.9983 x

Sodiumacetate 0.8850 0.9106 0.9728 0.9691 x

Olsen Modified 0.8720 0.8838 0.9525 0.9390 0.9845 x

Ca2+

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0

100

200

300

400

0 50 100 150 200 250

K-M

ehlic

h

K-KCl/CaCl

r2 = 0,9963

0

100

200

300

400

0 100 200 300 400

K-M

ehlic

h

K-Olsen

r2 = 0,9359

0

100

200

300

400

0 100 200 300 400

K-M

ehlic

h

K-Ammonium-Acetate

r2 = 0,9995

0

100

200

300

400

0 100 200 300 400K-A

mm

oniu

mac

etat

e

K-Olsen

r2 = 0,9271

Comparison of different soil extraction methods

K+

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KCl NaCl Mehlich Ammonium-Acetate

Sodium-Acetate

Olsen „Modified“

KCl xNaCl 0.9951 xMehlich 0.9963 0.9965 xAmmoniumacetate 0.9961 0.9978 0.9995 xSodiumacetate 0.9965 0.9988 0.9991 0.9995 xOlsen Modified 0.9198 0.9196 0.9359 0.9271 0.9320 x

Comparison of different soil extraction methods

K+

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For Magnesium all methods show a high significance to each other (r2 = 0,98 – 0,99)

For Calcium only Ammonium-Acetate vs Mehlich-3 and Sodium-Acetate vs Olsen „Modified“ show a high significance (r2 = 0,98 – 0,99)

For Potassium only the method Olsen „Modified“ is not significant to all other methods

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Relation between cations in soil solution andinterchangeable part

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How is the nutrient availability with water in comparison with the interchangeable cationsof each extraction method?

Is there a relation between cations in the soil solution and the interchangeable part?

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Waterversus

Ca(r2)

Mg(r2)

K(r2)

NaCl 0,4444 0,4402 0,9724

KCl 0,4303 0,4992 0,9856

Mehlich 3 0,6182 0,5365 0,9692

Ammonium-Acetate 0,6436 0,5609 0,9679

Sodium-Acetate 0,7064 0,5564 0,9715

Olsen „Modified“ 0,6210 0,5024 0,8944

Relation between cations in soil solution andinterchangeable part

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Conclusiones

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- Water shows poor correlations of measured Mg and Ca contents to all extraction methods, only the measured K showed a good correlation

- The extracted amount of cations differ from the method used

- For Magnesium all methods showed a high significant correlation, in the case of Calcium the correlation was not as good as Mg and K

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ConclusionesK+S KALI GmbH

- In the case of Mg the Ammonium-Acetate method showed the highest interchangeable nutrient content

- the nutrient level found was „very high“ compared to „low“ (with KCl and Olsen „Modified“)

- Nevertheless the Ammonium-Acetate method showed highly significant correlations to the other methods

- For fertilizer recommendations based on soil tests the interpretation of the results is very important and should analyzed carefully => a comparison of the leaf nutrient-level is recommended

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The End

26Date (YYMMDD), title, author/sign

Acknowlegdement

Thanks to Diego Monteros from FERMAGRI S.A. for providing me the soil samples analysed in this investigation

Thank you very much !