Yangbo He Soil Science Department

Sodic soil characterization and management on subsurface drainage

Yangbo “Kathy” He and Tom DeSutter Soil Science Department

WRRI Fellowship Research Presentations

7 February 2013

Sodic soils definition and distribution Table 1. Global distribution of salt affected soils (Szabolcs, 1989). Continent Areas in millions of ha

Saline† Sodic (Alkali)‡ Total

North America 6.2 9.6 15.8 Central America 2.0 — 2.0 South America 69.4 59.6 129.0 Africa 53.5 27.0 80.5 South Asia 83.3 1.8 85.1 North & Central Asia 91.6 120.1 211.7 Southeast Asia 20.0 — 20.0 Australasia 17.4 340.0 357.4 Europe 7.8 22.9 30.7 Total 351.5 581.0 932.2

Type ECe ESP SARe pH

Saline >4 <15 <12 <8.5

Sodic <4 >15 >12 >8.5

Salt affected soils (NRCS)

Biscuit top Btn

A E

Btn

Btnz

Btknz

Bkz Bk

C

Exline, Fine, smectitic, frigid Leptic Natrudolls

E

Btn1

Btn2

Bg1

Bg2

Cg

Ryan, Fine, smectitic, frigid Typic Natraquerts

Photo by M. Ulmer Photo by Y. He

Sodic soils • 4.7 million acres of sodic soil in ND • Many sodic soils are under CRP or

rangeland • Increase in commodity prices has allowed

for the conversion of CRP to crop production

Productivity index of sodic soils (depends on the county where the soil is located)

Highly sodic soils PI Medium PI Productive soils PI

Exline 30 Bearden-saline 54 Fargo 86

Stirium 22 Antler-saline 52 Glyndon 93

Ryan 42 Gardena 94

Ojata 24

“normal” soil flocculation Ca2+

Mg2+ NH4

+ K+

Ca2+

Mg2+ NH4

+ K+

Na+

Na+ Na+

Na+

How Na+ cause soil structure problems?

But with excess Na+ and low EC, there is dispersion

Na+ cause adverse effects on soil structure

Flocculation occurs when the monovalent cations (i.e. Na+) is replaced by divalent cations (Ca2+) and “clumping” of soil particles occurs. Dispersion: soil is separated into individual particles (opposite of flocculation)

http://www.agric.wa.gov.au/objtwr/imported_images/fn_386_figure2.jpg

Mechanism of Na+ adverse effects

• Guoy-Chapman theory

(Essington, 2004)

( )IZ

k10

1 10042.3 −− =

If the double layer is small, no dispersion

At low EC, thickness of double layer is large, Double layers of adjacent particles will overlap, causing electrostatic repulsion

Effect of ionic strength (I)

Effect of ion charge (Z)

Ca Na

From Essington, 2004

Water Management

• Tile drainage is an effective water management tool

• Drainage performance may decrease – Soil chemistry change – Being placed in or below a zone of sodic subsoils

• Cost is expensive ($400-800/acre; average charge of $576/acre (Aakre)

Data collected and summarized by David Franzen, NDSU, February 2013

Potential impact from drainage

A

E

Btn

H2 O

Flow

GW

A

E

Btn

Drainage tile

H2 O

Flow

After 6 h

Start

Management

A

E

Btn

Drainage tile

EC decrease H2 O

Flow

Drainage tile

Gypsum application

NG G

A

E

Btn

Ca

Ca2+ & EC

Na+

What to do?

• Currently no management guidelines for draining or remediating sodic or saline/sodic soils.

• Most sodic soil work is done dryland or irrigated soils, not tile-drained soils.

• Principle theories are the same but the management may be different.

Soil Management • Complicated…

– gypsum, spent lime, reactive area, application rate, soil chemical properties, location of sodic zone, subsurface vs surface drainage, gravitational water vs capillary water…

– Cost of gypsum is about $200/ton; sugarbeet spent lime is “free”

– Potential agricultural use of flue gas desulfurization gypsum in ND

– The application rate is now based on local experience and financial consideration

– No proper rates have been determined for ND soils

• Objectives Determine effects of gypsum or spent

lime on sodic soil reclamation or soil “maintenance”

Investigate gypsum or spent lime dissolution/precipitation, Ca and exchangeable Na on exchange phase

Develop proper rates for application based on different soil series and characteristics

Field sampling and soil characterization

• Soil series Sodium-affected soils:

Ryan, Stirum, Exline, Ojata Potentially sodium-affected subsoils:

Antler-saline, Bearden-saline, Colvin Very productive soils:

Fargo, Glyndon, Gardena

3 reps/series (the same delineation) 0-6’’, 6-12’’, 12-24’’,and 24-36’’.

• Sampling

Laboratory sodic soil characterization

• Measurement – Ksat, pore volumes of water – Dispersion (Panayiotopoulos et al., 2004),

– Swelling (Curtin et al., 1994) – Exchange reactions – Mineralogy of clays

Materials and Methods

Current Gypsum Recommendations

• Detailed chemical characterization are

necessary before gypsum or spent lime (Ca2+), and drainage management

• Regional specific Ca-amendment application

requirements will be developed for both sodic and non sodic soils.

Summary

Acknowledgements: Partial funding provided by NDWRRI and by NRCS CIG