Chemistry of Sodium-Affected Soils

Chemistry of Sodium-Affected Soils Dr. Tom DeSutter and Yangbo Kathy He Associate Professor of Soil Science Program Leader for Soil Science North Dakota State University 2 nd Annual Reclamation Conference 25 February 2014

DeSutter et al, 2014 unpublished data

0.800 0.700 DeSutter et al, 2014 unpublished data flux (cm/h) 0.600 0.500 0.400 0.300 Flux (cm/h) Start Brine Stop Brine 0.200 0.100 0.000 8/21/12 12:00 AM 8/22/12 12:00 AM 8/23/12 12:00 AM 8/24/12 12:00 AM 8/25/12 12:00 AM

Why does this happen? Na inflicts two different possibilities: Dispersion Internal swelling Both of these are a function of the concentration of Na and the EC of the soil solution

Photo by Tom DeSutter

Theory of dispersion Effect of ionic strength (I) (Essington, 2004) Guoy-Chapman theory k 1 3.042 10 = Z 10 ( ) I Effect of ion charge (Z) Ca Na At low EC and monovalent cations, thickness of double layer is large, Double layers of adjacent particles will overlap, causing electrostatic repulsion.

Na + SAR e = Ca 2+ + Mg 2+ 2 ESP= Na* 100 CEC

Lab data of dispersion Montmorillonite SAR =24 EC= 0.5, 2, 4, 6, 8, 12, and 16 ds/m

Relative %of dispersed clay (%) 80 60 40 20 0 80 60 40 20 0 Montmorillonite SAR=24 SAR=5 80 60 40 20 0 80 60 Clay dispersion decreases with a decrease in SAR and 40 an increase in EC 20 0 SAR=12 SAR=1 0 2 4 6 8 10 12 14 16 0 2 4 6 8 10 12 14 16 EC (ds m -1 ) He, Y., T. DeSutter, and D. Clay. 2013. Dispersion of pure clay minerals as influenced by Ca to Mg ratios, SAR and EC. Soil Sci. Soc. Am. J. 77:2014-2019.

Lab data of dispersion Dispersed clay concentration (g/l) 20 15 10 5 0 SAR= 24 Montmorillonite 0 2 4 6 8 10 12 14 16 18 20 15 10 5 SAR=24 Illite 0 0 2 4 6 8 10 12 14 16 18 EC (ds/m) 20 15 10 5 0 SAR=24 Kaolinite 0 2 4 6 8 10 12 14 16 18 He, Y., T. DeSutter, and D. Clay. 2013. Dispersion of pure clay minerals as influenced by Ca to Mg ratios, SAR and EC. Soil Sci. Soc. Am. J. 77:2014-2019.

Lab data of dispersion Dispersion is as a function of both amount of Na and EC Dispersion increase with SAR and decrease with increase of EC for 2:1 type clays (Mont. & Illite) 6 5 4 Dispersion SAR 3 2 1 0 0 1 2 3 4 5 6 EC Adverse effects of dispersion can be alleviated by increasing the solution EC (but plants may suffer)

Swelling theory Na + has little interruption on water net in interlayer, the water is retained and fluidity is reduced Ca 2+ disrupts water net allowing water to more mobile, reduces overall swelling Na + Na + Na + Ca 2+ Interlayer space H 2 O enter in and cations hydrated Na + Na + H 2 O Ca 2+ H 2 O H 2 O H 2 O H 2 O H 2 O Repulsion > attraction force, interlayer space increase, clay swell (Grim, 1968)

32 Wyndmere CIG Field Soil SAR = 14 30 % Water (1/3 bar) 28 26 24 22 20 18 Reference He et al, 2014 unpublished data 16 0 2 4 6 8 10 12 14 16 EC (ds/m; mmhos/cm)

Adverse effects on water movement Na and EC Control swelling and dispersion Reduced soil pores and clogged soil pores by clay particles Slow down water movement (Ksat)

Adverse effects on water movement Ksat (Saturated hydraulic conductivity) with water Hydraulic conductivity (cm/h) 0.025 0.020 0.015 0.010 0.005 0.000 Exline soil series 7 14 24 28 SAR He et al, 2014 unpublished data

Now what? Steps to remediate/mitigate a Na-affected soil Need Ca amendment (other cations may work too) Need water for leaching Need drainage to get Na out of the system

When Ca and EC are provided, water movement improves Hydraulic conductivity (cm/h) 0.30 0.25 0.20 0.15 0.10 0.05 0.00 Ksat Gypsum solution Ksat FGDG (10 tons/acre) 7 14 24 28 SAR He et al, 2014 unpublished data No treatment High Ca and EC

Summary Swelling and dispersion are the major mechanisms controlling soil structure and H 2 O movement Closely related with soil Na and solution EC SAR between 0-8 should be acceptable for H 2 O movement If SAR >8, EC will be need to be 2 This may only hold true for SAR values less than 15 The higher the SAR the higher the solution EC values need to be

Acknowledgements ND Water Resources Research Institute USDA-NRCS Conservation Innovation Grant Reducing sodification in high risk northern Great Plains soils

Chemistry of Sodium-Affected Soils Dr. Tom DeSutter Associate Professor of Soil Science Program Leader for Soil Science North Dakota State University 2 nd Annual Reclamation Conference 25 February 2014

Summary Summary Gypsum (tons/acre-foot) required for SAR to be reduced to 8 CEC\SAR SAR 13 18 30 CEC Quantity of gypsum Quantity of gypsum Quantity of gypsum 10 0.9 1.7 3.5 20 1.7 3.4 6.9 30 2.5 5.1 10.2