Fellow: Yangbo He
Advisor: Thomas DeSutter, Ph.D., associate professor, Department of Soil Science, North Dakota State University.
Degree Progress: Ph.D. in Soil Science expected graduation in Fall 2014.

Many soils in ND are being drained through the use of subsurface tiles. The purpose of subsurface drainage is to 1) decrease excess soil water, specifically at times of planting and harvesting and 2) remove soluble salts from the root zone (Chatterjee and DeSutter, 2012; Franzen, 2007). However, as noted by Cihacek et al. (2012), many of the soils may be negatively impacted because sodium is part of the exchange complex. Sodium is known a dispersant and this dispersion or swelling is accelerated when the concentration of soluble salts is reduced, which will likely occur in tile-drained soils (Cihacek et al., 2012; Curtin et al., 1994a). Dispersion and or soil swelling can lead to decreased Ksat, water percolation, and increased runoff, and finally a decrease in drainage performance. Currently there are no management strategies that have been developed for tile-drained soils in to help combat the effects of high sodium and low electrical conductivity or to prevent these phenomena from occurring. Detailed interpretation of chemical factors involved in sodic soils during tile drainage is incomplete.

Project Objectives:

The main objective of this study is the characterization and management of sodic soils for tile drainage. The specific objectives include:

• Determine physical and chemical properties (Ksat, dispersion, swelling, and pore volumes of water) of sodic soils
• Develop management guidelines and treatment options for sodic soils that will be or have been subsurface drained

Progress:

Investigation of how pure clay minerals react under different sodicity and salinity levels was completed and paper with title of “Dispersion of pure clay minerals as influenced by Ca to Mg ratios, SAR, and EC” was published by Soil Science Society of America Journal (77:2014-2019). For the project for which I am seeking funding, the effect of solution electrical conductivity and sodicity levels on sodic soil water holding capacity has been completed. The manuscript is being prepared and plans to be submitted to the Journal of Soil and Water Conservation for review. The characterization of the spatial distribution of sodium as related to topography will be started in May 2014.

Significance:

The disruptive effect of sodicity on the soil structural stability is a function of swelling and dispersion. Both of these processes may lead to a reduction of water infiltration and movement. Swelling commonly occurs in 2:1 dominant type of clays (like the clays we have in North Dakota) when water enters into their interlayer region. In sodic soils, high Na+ exists compared to divalent cations (Ca2+ and Mg2+). The size of Na+ has little disruption on the water within the clay’s interlayer close to clay surface and thus as the soil is wetted, water moves from the solution phase to these interlayers, causing swelling. When Na+ is present the interlayer water is “rigid” and does not easily flow. Swelling is maximized when the concentration of Na+, expressed as SAR (sodium adsorption ratio), is high and the EC is low, conditions that are typical of the Btn horizon in most sodic soils. This condition may also occur as salts are moved through the soil profile via gravimetric water in tile-drained systems. Therefore, improving our understanding of how subsurface drainage impacts soil chemical and physical properties is required for improved management of both sodium-affected soils and subsequent soil water.

Related Publications:

     He, Y., T.M. DeSutter, and D. E. Clay. 2013. Dispersion of Pure Clay Minerals as Influenced by Calcium/Magnesium Ratios, Sodium Adsorption Ratio, and Electrical Conductivity. Soil Science Society of America Journal 77:2014-2019.

Conference/Presentation:

     He, Y., and T.M. DeSutter. “Advances in our Knowledge of Dispersion and Swelling with Soil Sodium and the Interaction of Sodium Chemistry with Soluble Salts”. Presented at North Dakota Agricultural Association, Annual meeting. January, 2014. Fargodome. (Presentation).