Managing Saline Soils in North Dakota (continued)
Click here for an Adobe Acrobat pdf version suitable for printing. (256 Kb)
Saline Soil Management
Tile drainage
In parts of the world which have natural, well-developed drainage systems of rivers and streams, the simplest way to solve a saline soil problem is to install tile drainage in the problem fields, leaching low-salt water through the soil profile, and thereby allowing the salts to be carried away from the field through tile lines and into drainage canals or natural waterways. Until recently, there has been little interest in tile drainage in North Dakota. However, some tile has been installed in the Red River Valley, and salinity has been reduced as a result in some fields. When investigating the feasibility of installing tile drainage, it is important to consider the outlet. The water must flow to some natural drainage, such as a river or stream. It should not be dumped into the neighbor's field. Working with USDA-NRCS (Natural Resource Conservation Service) and the North Dakota Water Commission should be a part of the planning and implementation process. Mitigation of affected wetland areas may need to be considered.
If drainage is physically possible, tile construction within fields is expensive. A tile system in a loam soil may require parallel tile lines about 200 feet apart, with a cost of approximately $500 per acre or more. Tile systems in silty clay loam, clay loams and clay textured soils are even more expensive due to the need for closer tile spacing. For some, the cost of tile drains will appear justified, given the increase in salinity during wet years, and crop losses due to excessive soil wetness and increased salinity levels. Investing in tile drainage, however, is a gamble, because a significant portion of years during a farming career will be dry in this region.
Some consideration for drainage should be made in irrigated lands, particularly if soils are rated conditional due to drainage and salinity hazard. In western irrigated states, leaching soils periodically with large volumes of additional irrigation water following harvest drains away the buildup of salts in conditional soils and prepares the land for seeding the following year. Irrigation development on western lands is often conducted with as much consideration to tile drainage as for the irrigation system itself. Salinity and sodicity management are both controlled and managed with an irrigation/drainage system.
Tillage and seedbed preparation
Stand establishment is a critical crop yield factor for all crops, especially
in saline soils. Salts affect germination and emergence in a manner similar
to seedbed drying. Stand loss from poor emergence is directly proportional to
soil salt concentrations above a relatively low threshold level. Many crops
are much more sensitive to salt levels as a germinating seed and seedling than
as established plants (Table 1). Once a plant is established, it is normally
more tolerant of higher salt levels.
Table 1. Relative sensitivity to salts of
germinating and established crop plants.
-----------------------------------------
Salt Salt
tolerance of tolerance of
germinating established
Crop plants plants
-----------------------------------------
Alfalfa low low-medium
Barley high high
Corn medium low-medium
Dry bean very low very low
Sugarbeet low high
Wheat medium medium-high
-----------------------------------------
Salt levels in a seedbed can often be managed to acceptable limits. Seeding of spring-seeded crops on saline soils should be conducted to take advantage of the leaching potential of spring rains. One inch of rainfall can reduce salt concentrations by 50 percent in the one- to two-inch depth seedbed required for most crops grown in North Dakota. Lowering salt concentration in the seed planting zone can provide a dramatic increase in germination and seedling survival.
No-till or reduced/minimum tillage systems which use shallow tillage are recommended for seedbed preparation in saline soils. Salts leached away by winter snow melt and spring rains can be returned to the surface by deep spring tillage. Fall tillage should also be evaluated on the basis of spring seedbed preparation needs and relative salt levels in the tillage depth. Most deep tillage operations on saline land unnecessarily increase surface salt concentrations.
Soil testing for salinity
Soil areas that are severely affected by salts often have a bright white, crusty appearance when dry. The severity of the saline area usually extends well beyond the obvious area. In areas lacking a surface crust or obvious vegetation loss, salts are dissolved in soil water and cannot be seen. Therefore, the extent of the problem can only be identified with a soil test.
Soil testing laboratories use the electrical conductivity (ECe) of a soil extract to measure salt concentrations. Laboratories use strict procedures and check samples to ensure precision and accuracy of the test results. Personal handheld conductivity sensors are available through farm supply catalogues which may be less accurate than a lab, but with calibration would provide some indicator of the presence and severity of soil salinity to individual farmers and crop consultants.
There are also larger tools for spatial mapping available (Figure 6), such
as the EM-38 (Geonics, Ltd, Missis-sauga, Ont.) and pull behind soil-contact
sensors such as the Veris EC sensor (Veris, Inc., Salina, Kan.). These can be
used to make field measurements quickly and help define saline area boundaries.
These sensors will give relative levels of salinity, but the readings cannot
be translated into laboratory EC values. Directed measurements are important,
because when a composite soil sample is taken to represent a field, areas of
high and low salinity are mixed and results may paint an unrepresentative picture
of salinity status.
Figure 6. Veris conductivity sensor (left), EM-38 in use. (Norm Procnow and Hal Weiser, USDA-NRCS, Jamestown, N.D.)
Measurements should be taken within the suspected saline area, some just outside the most affected land, and another at some distance surrounding the area in order to properly map the field. Field ECe levels can be extremely variable within short distances. Knowing what the salinity patterns are in the field can improve a salinity management strategy.
Electrical conductivity is a low-cost analysis. The results are either reported as decisiemens/meter (dS/m) or as millimhos/cm (mmhos/cm). One dS/m equals one mmoh/cm, so the terms are equivalent. Data, charts and papers can be found which use both terms.
Laboratories measure ECe on different soil to water extracts because of their convenience to the laboratory. The most common commercial laboratory measurements are made on extracts from either a saturated paste or a 1:1 by weight soil-to-water slurry. The saturated paste extraction is a more precise method used by the scientific community, but it is time-consuming and expensive. The 1:1 soil:water slurry method is a simple, rapid, low-cost and excellent procedure for screening problem soil sites and is the procedure used by the NDSU Soil Testing Laboratory.
Results can roughly be converted back and forth from a 1:1 slurry to a saturated
paste, using the following formulas in Table 2. These formulas are not well
calibrated and are only included as a rough guide for interpreting data from
the literature to data seen on most commercial soil tests.
Table 2. General conversion from 1:1 soil:water slurry
used by many commercial labs and the saturated paste
extract method used in research applications.
x = Ece of saturated paste extract
y = Ece of 1:1 soil:water slurry
----------------------------------------------------------
Soil Texture
----------------------------------------------------------
Coarse Medium Fine
----------------------------------------------------------
x = 3.01y - 0.06 x = 3.01y - 0.77 x = 2.96y - 0.95
y = 0.33x + 0.06 y = 0.33x + 0.77 y = 0.375x + 0.97
----------------------------------------------------------
Crop tolerance
Crops have different tolerance levels for salt concentrations. All crops have a maximum salt level they can tolerate without a yield loss. Salt levels above a crop's maximum tolerance level sharply reduce yields.
The generally accepted soil salinity ratings for field crops, pasture and hay grasses and vegetables are shown in Tables 3 through 5, respectively. The tables show tolerance levels developed using the saturated paste extract, and also include estimates of thresholds using the 1:1 soil:water slurry method. The estimated effects of common crop yields on soils of increasing EC are shown in Table 6. When reading the tables, it is important to realize that the values do not come from an average of hundreds of cultivars of each crop or plant. The values are related to the limited scope of one to several experiments under one to several environments. Our experience in North Dakota shows that there is a wide range of intolerance to tolerance to salinity in most crops.
The tables show that certain crops such as dry bean need to be grown in fields with lower salinity, and that profitability in fields with higher EC would increase with more highly tolerant crops. When fields of intermediate to higher salinity (greater than EC 1.0 mmoh/cm, generally) are encountered, discussing the higher salt conditions with a knowledgeable seeds person and obtaining a higher yielding, more salt tolerant variety would be wise.
The tables do not account for the presence of other stresses. In soybean, for
example, the tables represent the tolerance of that crop to salts in the absence
of iron chlorosis. However, Red River Valley studies (Franzen and Richardson,
2000) show that when chlorosis is present, the threshold salinity is close to
EC 1.0 . The table values, therefore are not predictors of what will happen
in the field. They should be considered as representative of differences between
crops, but actual responses in the field will be modified for better or worse
by environmental and management related stresses or improvements from "normal"
conditions.
Table 3. Crop salt tolerance ratings, row crops and grains, annual forages.
-------------------------------------------------------------------------------------------------------
% Yield Ece at
Threshold Salinity decrease 70% yield
------------------- -------- ---------
1:1 Saturated % per Relative tolerance*
soil:water paste dS/m saturated ------------------
slurry, method, saturated paste
Crop dS/m** dS/m paste dS/m S MS MT T Source
-------------------------------------------------------------------------------------------------------
Alfalfa 1.4 2.0 7.3 6.1 X Bernstein & Francois, 1973
Barley 3.4 8.0 5.0 14.0 X Hassan et al., 1970a
Beans, dry 1.1 1.0 19.0 2.6 X Osawa, 1965
Canola (rapa) 4.0 9.7 14.0 11.8 X Francois, 1994
Canola (napus) 4.4 11.0 13.0 13.3 X Francois, 1994
-------------------------------------------------------------------------------------------------------
Chickpea - - - - X Manchanda & Sharma, 1989
Corn 1.3 1.7 12.0 4.2 X Hassan et al., 1970b
Crambe 1.4 2.0 6.5 6.6 X Francois & Kleiman, 1990
Flax 1.3 1.7 12.0 4.2 X Hayward & Spurr, 1944
Millet - - - - X Maas & Grattan, 1999
-------------------------------------------------------------------------------------------------------
Oat - - - - X US Salinity Lab, 1954
Potato 1.3 1.5 14.0 3.7 X Bernstein et al., 1951
Rye 4.5 11.4 10.8 14.2 X Francois, 1989
Safflower - - - - X Francois & Bernstein, 1964
Sorghum 3.0 6.8 16.0 8.7 X Francois et al., 1984
-------------------------------------------------------------------------------------------------------
Soybean 2.4 5.0 20.0 6.5 X Bernstein & Ogata, 1966
Sudangrass 1.7 2.8 4.3 9.8 X Bower et al., 1970
Sugarbeet 3.1 7.0 5.9 12.0 X Bower et al., 1954
Sunflower 2.4 4.8 5.0 10.8 X Francois, 1996
Wheat 2.8 6.0 7.1 10.2 X Asana & Kal, 1965
Wheat, semidwarf 3.6 8.6 3.0 18.6 X Francois et al., 1986
Wheat, durum 2.7 5.9 3.8 13.8 X Francois et al., 1986
-------------------------------------------------------------------------------------------------------
* S = sensitive, MS = moderately sensitive, MT = moderately tolerant, T = tolerant
**estimated value based on a medium soil Table 4. Crop salt tolerance ratings, pasture and hay grasses.
-------------------------------------------------------------------------------------------------------
% Yield Ece at
Threshold Salinity decrease 70% yield
------------------- -------- ---------
1:1 Saturated % per Relative tolerance*
soil:water paste dS/m saturated ------------------
slurry, method, saturated paste
Crop dS/m** dS/m paste dS/m S MS MT T Source
-------------------------------------------------------------------------------------------------------
Alkaligrass nuttal - - - - X US Salinity Lab, 1954
Alkali sacton - - - - X US Salinity Lab, 1954
Brome, smooth - - - - X McElgunn & Lawrence, 1973
Fescue, tall - - - - X Bower et al., 1970
Grama, blue - - - - X US Salinity Lab, 1954
-------------------------------------------------------------------------------------------------------
Ryegrass,
perennial 2.6 5.6 7.6 6.5 X Brown & Bernstein, 1953
Timothy - - - - X Saini, 1972
Wheatgrass,
fairway crested 3.2 7.5 6.9 11.8 X McElgunn & Lawrence, 1973
Wheatgrass,
intermediate - - - - X Dewey, 1960
Wheatgrass,
slender - - - - X McElgunn & Lawrence, 1973
-------------------------------------------------------------------------------------------------------
Wheatgrass,
tall 3.2 7.5 4.2 14.6 X Bernstein & Ford, 1958
Wheatgrass,
western - - - - X US Salinity Lab, 1954
Wild rye,
beardless 1.7 2.7 6.0 7.7 X Brown & Bernstein, 1953
Wild rye, canadian 4.5 11.4 10.8 14.2 X US Salinity Lab, 1954
Wild rye, russion - - - - X McElgunn & Lawrence, 1973
-------------------------------------------------------------------------------------------------------
* S = Sensitive, MS = Moderately sensitive, MT = Moderately tolerant, T = tolerant
**estimated value based on a medium soil Table 5. Crop salt tolerance ratings, vegetables.
-------------------------------------------------------------------------------------------------------
% Yield Ece at
Threshold Salinity decrease 70% yield
------------------- -------- ---------
1:1 Saturated % per Relative tolerance*
soil:water paste dS/m saturated ------------------
slurry, method, saturated paste
Crop dS/m** dS/m paste dS/m S MS MT T Source
-------------------------------------------------------------------------------------------------------
Bean 1.1 1.0 19.0 2.6 X Osawa, 1965
Cabbage 1.4 1.8 9.7 4.9 X Bernstein & Ayers, 1949
Carrot 1.1 1.0 14.0 3.1 X Bernstein et al., 1964
Corn, sweet 1.3 1.7 12.0 4.2 X Bernstein & Ayers, 1949
Cucumber 1.6 2.5 13.0 4.8 X Ploagman & Biehuizen, 1970
-------------------------------------------------------------------------------------------------------
Lettuce 1.2 1.3 13.0 3.6 X Bernstein et al., 1974
Muskmelon 1.1 1.0 8.4 4.6 X Shannon & Francois, 1978
Onion 1.2 1.2 16.0 3.1 X Hoffman & Rawlins, 1971
Pea 1.9 3.4 10.6 6.2 X Cerdá et al., 1982
Pepper 1.3 1.5 14.0 3.6 X Osawa, 1965
-------------------------------------------------------------------------------------------------------
Pumpkin - - - - X Maas & Grattan, 1999
Radish 1.2 1.2 13.0 3.5 X Hoffman & Rawlins, 1971
Squash, zucchini 2.4 4.9 10.5 7.8 X Graifenberg et al., 1996
Strawberry 1.1 1.0 33.0 1.9 X Osawa, 1965
Sweet potato 1.3 1.5 11.0 4.2 X Greig & Smith, 1962
-------------------------------------------------------------------------------------------------------
Tomato 1.6 2.5 9.9 5.5 X Bierhuizen & Ploagman, 1967
Turnip 1.1 0.9 9.0 4.2 X Francois, 1984
Watermelon - - - - X deForges, 1970
-------------------------------------------------------------------------------------------------------
* S = sensitive, MS = moderately sensitive, MT = moderately tolerant, T = tolerant
**estimated value based on a medium soil Table 6. Relative crop yields at increasing levels of soil EC.
-----------------------------------------------------------------------------
Electrical conductivity, Ece dS/m, saturated paste method
-----------------------------------------------------------
2 4 6 8 10 12 14 16 18 20 22 24
-----------------------------------------------------------
Crop Percent (%) of maximum yield potential
-----------------------------------------------------------------------------
Alfalfa 100 85 71 56 42 27 12 0 0 0 0 0
Barley 100 100 100 100 90 80 70 60 50 40 30 20
Canola (napus) 100 100 100 100 100 87 61 35 9 0 0 0
Corn 96 72 48 24 0 0 0 0 0 0 0 0
Dry bean 81 43 5 0 0 0 0 0 0 0 0 0
Flax 96 72 48 24 0 0 0 0 0 0 0 0
Soybean 100 100 90 50 10 0 0 0 0 0 0 0
Sugarbeet 100 100 100 97 85 73 61 49 37 25 13 0
Sunflower 100 100 97 87 77 67 57 47 37 27 17 7
Wheat, durum 100 100 100 96 88 80 72 64 56 48 40 32
Wheat, semidwarf 100 100 100 92 84 76 68 60 52 44 36 28
-----------------------------------------------------------------------------
The NDSU Extension Service does not endorse commercial products or
companies even though reference may be made to tradenames, trademarks or service
names.
This publication may be copied for noncommercial, educational purposes in its entirety with no changes. Requests to use any portion of the document (including text, graphics or photos) should be sent to NDSU.permission@ndsu.edu. Include exactly what is requested for use and how it will be used.
For more information on this and other topics, see: www.ag.ndsu.edu
SF-1087 (revised), March 2007
