Soil Salt Management and Impact of Tile Drainage (Site 3)

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:

In June 2016, four sites were soil sampled in a field tiled drained. The field is located in Kingsbury County, SD. The soil samples locations were at the NE corner of the field and along the east central location. At both sites, soils samples were collected in the salt affected areas and non‐salt adjacent areas.

Soil samples were collected in June 2016 from 2 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 Points 1 and 2, tiled and non‐tile areas are presented in Table 1.

Results: 

Soil test analysis of these two field points would suggest that these soils are classified as a ‘saline‐sodic’. The soils have high salt concentrations over the 0‐24 inch sampling depth as indicated by EC > 4.0 μS/cm. The average soil EC over all depths and sites is 9.2. The soil sodium content is high for all sampling depths; the average across all four sites and depths is SAR = 9.6. SAR > 5.0 suggests that problems associated with too much sodium may start to become apparent.

The PPM sodium is high in the 12‐24 inch depth Point 1, Tile. In the ‘Supplemental Soil Information’ section of this report, ‘Stickney’ soil series is mapped at this site. The Stickney soil has elevated sodium concentrations starting at about 12 – 13 inch depth and extending 16 inches down approximately to 29 inch depth. The elevated sodium in the test sample may be indicative of this sodic horizon. Point 2, No Tile also has high sodium at the surface. The surface soils is dispersed at this site in 2016.

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’ and ‘Web Soil Survey‘;

https://casoilresource.lawr.ucdavis.edu/gmap/ 

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 both Point 1 and Point 2 is a Houdek‐Stickney‐Tetonka complex, 0 to 2 percent slopes. The estimated major soil series at Point 1 is 45% Houdek, 25% Stickney, and 20% Tonka (Figure 3A and
B). The estimated predominant soil series present at Point 2 is 50% Houdek and 40% Stickney.

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.

Houdek Soil Series: Houdek soil series is the predominate soil in this location at 45% and is the South Dakota state soil Figure 4A). 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 Houdek is classified as prime farmland if drained. A ‘Bt1 and Bt2’ comprise the 2nd and 3rd horizons (Figure 4A). The ‘t’ subscript in the ‘Bt’ horizon indicates that an accumulation of silicate clay that has formed and subsequently translocated within the horizon; this horizon had higher % clay than horizons above or below without the ‘t’ suffix letter. The 4th and 5th horizons are Bk1 and Bk2. The ‘k’ indicates that calcium carbonate (CaCO3) or lime is accumulated or present in the horizon. Calcium carbonate has a low soil water solubility and is typically not a salt of concern in a saline area (Table 2). The Houdek soil series does not have saline or sodium management issues.

Stickney Soil Series: The second predominant soil series is Stickney (Figure 4B). The LCC for this soil is a 3s. The ‘s’ indicatesthat soil characteristics limit its use as farmland. This soil provides the salt source that impacts plant growth and soil physical characteristics. This soil has a horizons (4‐7, Figure 4B) labeled ‘Btn1’, ‘Btn2’,‘Btn3’, and ‘Btnz’ starting approximately 13 inches from the surface and extending 16 inches to a maximum depth of 29 inches.

The lowercase letter ‘n’ in horizons 4‐7 indicates sodium salt accumulations. The term used by soil scientists to describe this horizon is a ‘natric’ horizon (‘Bn’). These horizons also have accumulated clay (Bt). Water infiltration of a soil horizon with the ‘Btn’ designation may be slowed from (1) dispersion due to sodium and (2) fine texture from clay. Horizons 7‐9 are labeled with ‘z’ descriptor. A ‘Bz’ horizon had accumulation of salts more soluble than gypsum (CaSO4).

A ‘y’ descriptor indicates an accumulation of gypsum, ‘By’. Presence of gypsum in the soil horizons is not mapped at this site. However, due to the accuracy of the soil survey maps and the age, presence or absence of gypsum could be identified with soil tests and physical examination of the soil horizons. The Stickney soil may potentially have management issues associated with sodium.

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. The author would also like to thank the producers who participated in this study.