Soil Salt Management and Impact of Tile Drainage (Site 5)

Site Location:
In June 2016, four sites were soil sampled in a field tiled drained and another field that was not tile drained. The fields are located in Brown County, SD. The soil
samples locations were at the North West area of the field (tile present). The no‐tile field was directly N of the tiled field across the road (Figure 1 & B).

Introduction:

Soil Test Data:
Soil salt issues are classified as either saline or sodic. Soils with high total salts are defined ‘saline’. Soil samples were analyzed for salinity by measuring soil electrical conductivity (EC, unit are mS/cm). For eastern SD soils, if the soil EC is > 4.0, the soil contains a high salt concentration. Predominate salts in eastern SD soils are calcium (Ca+2), magnesium (Mg+2), and sodium (Na+1). Soils with high salts have poor seed germination. Abundant presence of sodium salts provides an additional management issue.

Soils with high sodium concentration have poor seed germination and are prone to dispersion and drain issues. The term used to describe a soil with too much sodium is ‘sodic’. In a dispersed soil, water infiltration is slowed. If the soil texture contains high amounts of clay in addition to the sodium, water infiltration if further inhibited. Sodic affected soils erode easily due to poor soil structure and water infiltration. Soil testing labs use one of two indexes to measure sodium, sodium absorption ratio (SAR) or exchangeable sodium percent (ESP). Research at both South Dakota and North Dakota suggest that SAR or ESP values > 5.0 are soils with high sodium contents that are prone to dispersion.

Methodology:

Soil samples were collected in June 2016 from 4 points in the field where salt issues were apparent on surface soils. Soil samples were collected at points shown in Figure 1. Samples were collected from tile and non‐tiles areas. Twenty cores were collected in a 20 foot radius around the point. Samples were collected over 4 depths, 0‐3, 3‐6, 6‐12, and 12‐24 inches. The soil samples was analyzed for (1) EC, (2)
parts per million (PPM) sodium, and (3) sodium absorption ratio (SAR).

Soils were prepared for lab analysis at South Dakota State University. Soil analysis was completed at North Dakota State University. Cation concentrations analyzed at North Dakota State using inductively‐coupled plasma spectrometry (Optima 5300V, PerkinElmer, Waltham, MA) or an atomic absorption spectrometer (Model 200A, Buck Scientific, East Norwalk, CT). Soil test results for Tile North 1, 2, 3 and No Tile North Wheat are presented in Table 1.

Results:

Soil test results for Tile North 1, 2, 3 and No Tile North Wheat are presented in Table 1.

Soil test analysis of Tile North 1 top 3 inches is classified as a ‘saline’ since EC = 7.0 (EC > 4.0 = saline). The lower soil sampled depth of 3‐24 inches is classified as ‘normal’ soil. Sodium is not an issue at this site, SAR = 2.7. Tile North 2 site is a ‘saline / sodic soil’ (EC > 4.0 and SAR > 5.0). The PPM sodium is highest (1280 PPM) in the 6‐12 soil sampling depth at Tile North 2 site.

Tile North 3 site is a sodic site since SAR > 5.0 for all sampling depths. The site to the north of the field where no tile has been installed, No Tile North (Wheat) is considered a ‘borderline saline’ soil. The EC = 4 (0‐3 inch depth) and EC = 5 (12‐24 inch depth) suggests that salts are present at this site.

Source of Salts:

Surface salts are present in the SW part of this field on the Web Soil Survey image. In the ‘Supplemental Soil Information’ section of this report, the ‘GS873A’ Beotia‐Winship silt loam soil series is mapped at this site. These soils series do not have horizons salt accumulations (Figure 4A and B).

The question is, what is the salt source in these soils? The Pierre Shale is the uppermost (close to the ground surface) geological bedrock formation in Brown County. This shale was deposited from 65‐145 MYA when a shallow inland ocean occupied this area.

The Pierre carries the salt signatures of this old ocean bed and is high in salt. As the glaciers moved over the landscape, parts of this shale was pulverized from the weight of the glacier and incorporated into the glacial till. The glacier acted as slow, massive, field cultivator that passed over the old ocean deposits at different depths; the mixing was not homogeneous or all the same. As the ice melted, areas where salty shale minerals were mixed with till were deposited at a random pattern over the current landscape. Hence the reason for sporadic nature of soils with salts found in landscapes in this area. Concern arises over managing water in these non‐salt affected soils. Is salt laden ground water flowing into adjacent non‐salt soils and slowly expanding the problem over time?

Objective:

The objective of this study is to monitor these sites on annual basis. The functionality of the tile to remove salts will be evaluated through annual soil sampling over the course of 3 years. The non‐tile adjacent sites will serve as a comparison to monitor how well tile works to remove salts from the upper
horizons of these soil profiles.

The 2016 soil data is year one of a 3‐year study. Subsequent years will be compared to the 2016 baseline data to create a database regarding if agriculture drain tile removes salts accumulated in upper soil horizons. Further information regarding soil characteristics at this site is provided under the section ‘Supplement Soil Information.’

Supplement Soil Information:
Imagery from this section was collected from ‘Soil Web’ https://casoilresource.lawr.ucdavis.edu/gmap/
and ‘Web Soil Survey’, https://websoilsurvey.sc.egov.usda.gov/App/WebSoilSurvey.aspx.

Soil surveys are intended to describe the type of soils found in a general area. Soil series boundary lines between different soils are not always so obvious that the lines can be plotted with high precision on a map. Often part of one soil series or soil complex is commonly included in the delineation of an adjacent different mapping units. Many soil surveys were completed over 50 years ago. It is also reasonable to assume that soil series boundaries have changed over time with land management
changes.

Soil Map Information:

Soils mapped by NRCS Soil Survey are summarized in Figure 2A and B. The soil series mapped at all four sampling sites is Beotia‐Winship silt loams, 0 to 2 percent slopes.

The estimated major soil series at these four points is a Beota‐Winship (Figure 3A). In this soil series map unit, Beotia comprises approximately 64% and Winship, 23%. It should be noted none of the six soils mapped at this location contain salts.

Soil Series Descriptions:
Soil series descriptions represent an ‘average’ soil of that series. Horizon depths and thicknesses will vary some. However if the soil is mapped to have a ‘Btn’ horizon, this horizon should be present and easily identified in the soil series.

Beotia Soil Series:
The Beotia soil series comprises approximately 64% of the soils in this map unit (Figure 3A). The land capability class (LCC) is 2c. The LCC classifications range from 1 to 8. Soils with no limitations for use are classified as a 1. Typically farmland is classified as 1‐4 based on characteristics like slope, top soil depth (horizon A), drainage, texture, salt content, etc. The lower case ‘c’ is assigned based on climate
limitations most likely associated with a shorter growing season in the upper Northern Great Plains.

The soil is a very deep, well drained or moderately well drained soils formed in silty glaciolacustrine deposits on lake plains. This soil is classified as prime farmland. Horizons 5 and 6 are ‘Bk’ horizons (Figure 4A). These soils have lime accumulations as indicated by the ‘k’. Calcium carbonate has a low soil water solubility and is typically not a salt of concern in a saline area (Table 2).

Winship Soil Series:
The second predominant soil series is Winship (Figure 4B). This soil series consists of very deep, well drained or moderately well drained soils formed in silty glaciolacustrine deposits on lake plains. The LCC for this soil is a 2w. The ‘w’ indicates that water limits its use as farmland. Soil horizons 4 and 5 are ‘Bt’ indicating that clay is accumulated in this horizon. Water infiltration of a soil horizon with the ‘Bt’ designation may be slowed from fine texture from clay. This soil is classified as prime farmland. Note that the mapped soil series at this location does not suggest salts should be problematic in this area.

Acknowledgements:

Prepared by Cheryl Reese, SDSU Plant Science Department

Funding for this project is provided by SDSU Extension and the South Dakota Soybean Research & Promotion Council. On-farm research involves teaching, research and extension in partnership with funding agencies and local producers.