Soil Amendments on

Northern Plains

• Many soils in Northern Plains have high pH

(>7.3) and high salinity (salts)

• Farmers know these issues may reduce yields

and are always looking for the “easy button” to

“fix” these issues.

• Some people tell farmers a couple hundred

pounds of soil amendments can “fix” these

issues

• Elemental sulfur and gypsum are often

mentioned in these claims.

Soil Amendments

to reduce Soil pH

• If you could lower a soil pH from 8.0 to about

7.0 and keep it there, the availability of

nutrients, like phosphorus, will increase.

• Reducing pH (along with carbonates) may

also reduce IDC in soybeans.

• Will a couple hundred pounds of elemental

sulfur or gypsum lower soil pH?

Soil pH – Availability of Nutrients

Lowering soil pH may increase nutrient availability. (Soils

with free calcium carbonate have pH around 7.5 - 8.2.)

AGVISE – Soil Amendment

Project 2005-2017

• 10,000 lb/a Elemental Sulfur

Can 10,000 lb Elemental S

Lower Soil pH?

2S + 3O2 + 2H2O

Sulfur + Oxygen + Water Sulfuric Acid

Elemental sulfur must be mixed with moist, warm aerated

soil with bacteria (Thiobacillus) for this reaction to occur. The

hydrogen (H+) from the sulfuric acid lowers pH. If soil

contains carbonates (pH higher than 7.3), it will require very

high rates of sulfur to change pH permanently.

2H2SO4

H+ H+

Does Elemental Sulfur Lower Soil pH?

8.0

7.57.6 7.6 7.6

7.77.8 7.8 7.8 7.8

7.77.8 7.8 7.8

6

6.5

7

7.5

8

8.5

9

4-05 9-05 9-06 10-07 9-08 09-09 08-10 11-11 10-12 10-13 10-14 10-15 10-16 10-17

So

il p

H

Soil (CCE) Carbonate level is 1.5%, loam soil texture

10,000 lb/a elemental Sulfur tilled into soil April-2005

YES, but rate must be high and change may not be permanent

pH range with highest available P

70%

81%75%

50%

40%

61%

71%

85%

89%

41%

57%43%

76% 86%

84%81%

64%72%

% Soil samples with carbonate greater than 1.0%

Fall 2017 samples

(0-6” samples)

MB

ND

SDMN

88%

63%20%

73%

98%

75%

58%

39%

34%

54%

For most soils in this region, it is impossible to lower pH because carbonate will

neutralize acid.

• Reduced by 0.5 pH unit in first year, then

increased to near original pH.

• Calcium carbonate in soil was not completely

neutralized by elemental sulfur, so pH change

was not permanent and went back up.

• Since 10,000 lb of elemental S was not

enough to lower pH in 12 years, maybe we

will increase rate to 100,000 lb elemental S

next time!

• Couple hundred pounds won’t do it!!!

Effect of 10,000 lb Elemental

Sulfur on Soil pH

Farmers would like to lower

Salinity too! Can Elemental Sulfur

do that? (Soybeans would benefit)

Soybean tolerance to salinity (EC 1:1 method)

(NDSU, 2016).

1.71.9

2.11.8

2 2.3 2.4 2.3 2.32.1

2.3 2.22.4 2.5

0

0.5

1

1.5

2

2.5

3

3.5

4

4-05 9-05 9-06 10-07 09-08 09-09 08-10 11-11 10-12 10-13 10-14 10-15 10-16 10-17

mm

ho

s/c

m (

rou

tin

e 1

:1 s

alt

test)

Sulfur 10000

Does 10,000 lb/a Elemental

Sulfur Reduce Soluble Salts?

No – Salinity has gone up!

Effect of 10,000 lb Elemental

Sulfur on Salinity

• Salinity increased over time.

• Elemental sulfur reacted with calcium

carbonate (CaCO3) in soil to form gypsum

(CaSO4), which caused the salinity to

increase to about 2.2 mmhos/cm (conductivity

of saturated gypsum solution).

• Elemental S did not lower salinity in 12 years.

Salinity actually increased as we expected.

• Elemental S will not reduce salinity (salts).

AGVISE – Soil Amendment

Project 2005-2017

• 5,000 Gypsum

CaSO4

Does 5000 lb/a Gypsum (CaSO4)

Decrease Soil pH?

8.07.8 7.8 7.9 7.8 7.8 7.9 7.9 7.9 8.0 7.9 7.9 8.0

7.8

6

6.5

7

7.5

8

8.5

9

4-05 9-06 9-08 08-10 10-12 10-14 10-16

So

il p

H

5000 lb/a Gypsum tilled into top 6” of soil - April 2005

Loam Soil texture, Carbonate level (CCE) = 1.5%, poorly drained

No – pH has not changed!

Gypsum slowly dissolves

No chemical reaction to

change pH (No H+)

CaSO4•2H2O Ca2+ + SO42- + 2H2O

Gypsum calcium + sulfate + water

No H+ produced when gypsum slowly dissociates

into calcium and sulfate ions in the soil solution.

If no hydrogen (acid) is created, the soil pH

should not change!

Can Gypsum Lower Soluble Salts?

1.11.3

1.7

1.21.4

1.61.9

1.3 1.4

0.8

1.2 1.10.8

1.5

0

0.5

1

1.5

2

2.5

3

3.5

4

4-05 9-05 9-06 10-07 9-08 09-09 08-10 08-11 10-12 10-13 10-14 10-15 10-16 10-17

Sali

nit

y m

mh

os/c

m (

1:1

)

5000 lb/a Gypsum tilled into soil 4-26-2005

No! – Salinity has gone up and down with

normal variation based on precipitation

Effect of 5,000 lb Gypsum

on Salinity• Salinity varied over time corresponding to wet

and dry years, showing the role of water

movement on changing salinity level from

year to year.

• Gypsum is a slowly soluble salt that dissolves

in the soil solution. It dissociates into ions

which actually increase soil salinity.

• Gypsum did not lower the salinity in 12 years.

• Gypsum is not a useful amendment for

lowering soil salinity. Yet, it can be useful for

soils with high sodium.

• Apply more P fertilizer in bands

• Apply higher rates of P fertilizer

• Building P soil test levels is not easy in high

pH soils, but it is much less expensive than

trying to reduce the soil pH

• For IDC – (high pH soils with carbonates)

– IDC varieties, wide rows, Fe-EDDHA

What are viable alternatives?

Soil Amendments can’t

economically lower soil pH?

• Include more high water use crops in

rotation to lower the water table

– Corn, sunflower, alfalfa

• Keep something growing all season

– Cover crops, perennial grasses

• Improve surface drainage

• Tile drainage

What are viable alternatives?

Soil Amendments can’t

economically reduce salinity?

Tile drainage “can” lower salinity(along with crop rotations that use much water)

0

0.5

1

1.5

2

2.5

3

3.5

4

02 03 04 05 06 07 08 09 10 11 12 13 15 16 16 2017

Site 2 Site 5

Solu

ble

Sal

ts (

e.c.

mm

ho

s/cm

1:1

met

ho

d)

AGVISE Tile drainage Demo Project 2002-2017

Soil amendment “Myths” are here to stay!

Human nature is to look for the “easy button”

Lowering soil pH and salinity will

never be easy or inexpensive!

Beware promises of products saying this will be easy!

Demo project 2018

Liming very acid no-till fields

• Cooperators and sites needed

• Long-term no-till (10 plus years)

• Low pH topsoil (less than 6.0)

• Low pH subsoil (less than 6.5)

We will be applying lime and tracking effect of lime

through the topsoil over time. Incremental

sampling 0-2”, 2-4”, 4-6” testing pH and nutrients

Thank You

for your business

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