Field Crops - Salt Tolerance

Data from Salinity Laboratory, Riverside CA and U of Wyoming 1992

Field Crop (No spring flooding)	Salt Tolerance* mmhos/cm 1:1 method
Barley	3.5
Sugarbeets	3.0
Sunflower	2.5
Wheat	2.2
Oats	2.0
Sorghum	2.0
Canola	1.5
Sudan Grass	1.5
Corn	1.0
Potato	1.0
Beans	0.8

* Salt Level where yields decrease to about 75% of normal
Spring flooding not tolerated well by Field Crops

Forage Crops - Salt Tolerance

Data from Salinity Laboratory, Riverside CA and U of Wyoming 1992

Field Crop (No spring flooding)	Salt Tolerance* mmhos/cm 1:1 method
Tall Wheatgrass	5.0
Russian Wildrye	6.0
Altai Wildrye	5.0
Slender Wheatgrass	5.0
Crested Wheatgrass	3.5
Pubescent Wheatgrass	3.5
Intermediate Wheatgrass	3.5
Smooth Bromegrass	2.5
Yellow Sweet Clover	2.5
Birdsfoot Trefoil	2.5
Alfalfa	2.5

* Salt Level where yields decrease to about 75% of normal
Spring flooding not tolerated

Forage Crops - Salt Tolerance

Data from Salinity Laboratory, Riverside CA and U of Wyoming 1992

Field Crop (Tolerant to spring flooding)	Salt Tolerance* mmhos/cm 1:1 method
Beardless Wildrye	6.0
Tall Wheatgrass	5.0
Hybrid Wheatgrass	5.0
Slender Wheatgrass	5.0
Tall Fescue	4.0
Western Wheatgrass	2.7
Strawberry Clover	2.7
Creeping Foxtail	2.5
Meadow Bromegrass	2.2
Orchard Grass	1.3

* Salt Level where yields decrease to about 75% of normal
Spring flooding is tolerated

Saline (salty) soils cost farmers millions of dollars every year in lost yield and unproductive inputs. While we all wish for a magic chemical to neutralize or overcome the problems salts cause, we need to do what we can right now to improve yields on salt affected fields.

Reducing the affects of salinity revolves around managing the water in the soil profile. All salinity problems are caused by too much water! When the water table is close to the soil surface (less than 4 feet), water is wicked to the surface and evaporates away. The problem is, the salt is left behind at the soil surface (white crust). As the salt level increases at the soil surface, it becomes harder for plants to take up the water, because the concentration of salt in the soil solution is too high. If the salt level becomes high enough, some crops will not even survive (see table). Many field crops start having problems when the soil salt level increases to 1.0 mmhos/cm or higher. If the crop dies, and their is no water uptake by growing plants, the water table gets closer to the surface, more water and salts are drawn to the soil surface, and the salt problem gets worse.

The first step in managing saline soils is to remove the source of excess water. Surface drainage is crucial to keep standing water to a minimum in the spring. Most crops or salt tolerant forages cannot tolerate several weeks of standing water.

The second step in managing salt affected soils is to plant a grain crop or forage crop that can handle the salt levels present in the soil. It is critical to have plant growth removing water from the soil profile all during the growing season to keep the water table lower and the salt problem from getting worse. If the salt problem is only moderate, the crop rotation may include barley, wheat, sunflowers etc. If the salt problem is severe, salt tolerant forages may be the only choice (See table). When you are developing a plan to manage the salinity in a field, it is worth your time to divide the field into productivity zones for soil testing. Areas with high productivity likely have lower salt levels, which give you more cropping options. The salinity level can vary greatly from area to area within each field. Testing the salt level in these zones will tell you which crops will be productive in each area. In many situations, only a portion of each field needs to be planted to a very salt tolerant forage, while the rest of the field can remain in crops like barley, wheat, corn etc.

Once the surface water problem is removed and vegetation is established, tile drainage should be considered. Tile drainage allows the salts to be leached downward in the soil profile as the tile drainage removes the excess water and lowers the water table. The decrease in the salt level in tiled fields can be measured by soil testing each year. AGVISE has been monitoring the soil salt level in a field that was tiled three years ago (see figure). As you can see, the salt level over several tile lines started near 3.0 mmhos/cm three years ago and the salt level has dropped to about 1.5 or less. The yield on this particular field have improved greatly in the past three years. Managing salinity is a long-term process. Some people have suggested that applying gypsum (calcium sulfate) will greatly improve crop yields on salty soils. Some of the claims include "gypsum will lower the soil pH" and gypsum will "neutralize" the salt in the soil. To evaluate these claims, AGVISE has been monitoring the soil pH and salt levels following a gypsum application three years ago. As you can see in the figure, the soil pH has not changed in three years, even with an application of 15000 lb/a of gypsum. The salt level in the soil has actually increased in the sites where the gypsum was applied at rates higher than 300 lb/a. Higher salt levels decreases productivity, showing gypsum is not the answer. Managing the excessive water and keeping crops or forages growing is the key to improving yields on salt affected fields. There are no quick fixes in managing saline soils. Please give us a call if you have additional questions on managing saline soils.

If you would like to read more about GYPSUM try these articles:
Gypsum Magic
Gypsum Magic Part 2
Gypsum Magic Part 3

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