Soil Salt Management and Impact of Tile Drainage (Site 6)

Site Location:
In June 2016, three sites were soil sampled in a field; 2 were tiled drained and one was not tiled. The fields are located in Brown County, SD. The soil samples locations
were at the north central area of the field (tiled); along the west side field (tiled); and across the road to the south tile point 1 (no tile) (Figure 1A). The recently installed tile lines could be easily observed at this site (Figure 1B).

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, units 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 potentially drainage 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 3 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 South Tile Pt 1 is classified as a ‘normal soil’ because soil test EC < 4.0 in the top 0‐3 inches. However, the soil test values suggest that through depths 3‐24 inches, salts are becoming a management issue since the average EC = 4.3.

The Soil Tile Pt. 2 is a ‘saline / sodic soil’ (EC > 4.0 and SAR > 5.0). The PPM sodium averages 1350 from 0‐24 inches. The South No‐Tile Point is borderline saline; EC = 4.3. The 6‐12 sample depth SAR = 23 suggesting that sodium is high. However, this value will be verified in 2017 sampling season since the SAR of the other soil sample depths is only 1 or 2.

In the ‘Supplemental Soil Information’ section of this report, the ‘GS873A’ Beotia‐Winship silt loam soil series is mapped at South Tile Point 1 (Point along west side of field). These soils were summarized in Farm Report 1. These soils series do not have horizons with salt accumulations. ‘G725C’ Great Bend‐Zell‐Huffton silt loam, 6‐9% is the mapped soil at South Tile Pt 2. The Great Bend soil does not have horizons salt accumulations (Figure 4A). The Zell contains some gypsum (By; y =gypsum) (Figure 4B) and the Huffton soil series contain salts (‘z’ in the Bkz1 and Bkz2) in horizons 3 and 4 (Figure 4C).

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 estimated major soil series at these three 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 (Figure 3A).

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.

Great Bend Soil Series:
The Great Bend soil series comprises approximately 41% of the soils in this map unit (Figure 3A). The land capability class (LCC) is 2e (Figure 4A). 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 ‘e’ is assigned based on erosion problems most likely associated with soil texture.

The soil is a very deep, well drained or moderately well drained soils formed in silty glaciolacustrine (previous glacial lake) deposits on lake plains. This soil is classified as prime farmland. Horizons 3 and 4 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).

Zell Soil Series:
The second predominant soil series is Zell, mapped at 28% (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 4e. The lower case ‘e’ is assigned based on erosion problems most likely associated with soil texture. Soil horizon 4 is a ‘Bky’ indicating that both calcium and gypsum is accumulated in this horizon. Presence of gypsum may suggest that other salts are deeper in the profile than what is mapped to 60 inches.

Huffton Soil Series:
The third soil mapped is Huffton at 20% composition. This soil is mapped with salt horizons starting at 13 inches deep, extending for 17 inches to a depth of 30 inches. This soil is a potential source of surface salts through capillary rise if ground water table is elevated.

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 like to thank the producers who participated in this study.