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Planting Suitable Salt-Tolerant Crops Based on Soil Salinity Levels (05/23/19)

Soil salinity is a critical soil health issue that producers, ranchers and landowners face throughout North Dakota.

Soil salinity is a critical soil health issue that producers, ranchers and landowners face throughout North Dakota. Saline areas produce either poor stands or nothing at all, especially along the headlands (Figure 1). On average, producers spend $82 to $169 per acre just at the time of planting to plant soybean, spring wheat, canola and corn. That results in a net loss on these salty areas. A study by Brennan and Ulmer (2010) reported 5.8 million potential saline acres in North Dakota, these potential saline acres amounting to about 15% of the 39 million acres of cropland, pasture and rangeland in North Dakota.

Saline soils will have excessive levels of soluble salts in the soil water, which are a combination of positively and negatively charged ions (for example, table salt; Na+Cl-). High levels of ions (positive and negative) from soluble salts restrict normal water uptake by plant roots even when soils are visibly wet, resulting in drought-stressed plants (osmotic effect). The presence of salt in soils is the product of high salt levels in our groundwater. Shallow groundwater depth due to landscape position and/or higher than normal rainfall result in capillary rise of soil water, which then leads to the accumulation of excessive soluble salts (salinity) in the topsoil. The soil test needed to determine the levels of soluble salts is electrical conductivity (EC).

Management of saline areas starts by sampling the problem areas, having the samples analyzed by a certified soil lab for EC and planting a suitable annual salt-tolerant crop or a perennial salt-tolerant grass mix based on the EC results. Planting a crop that is sensitive to moderately sensitive to high salt levels will not only result in loss of revenue but will make the salinity issue worse. By establishing a good vegetative cover, under lower groundwater depths, good soil water infiltration and decent rain, excessive salts can leach out of the topsoil with time.

The NDSU research showed that soybean yields started declining at an EC of 1.1 mmhos/cm (measured by 1:1 soil-to-water ratio method) on sandy loam soils, whereas, fifty percent yield reduction was observed at EC of 1.9 mmhos/cm (Butcher et al., 2016). So ideally, soil EC levels should be 0.5 mmhos/cm or less for most of the crops grown in North Dakota.

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Once soil EC levels are known, soybean will not be a suitable crop if the EC levels are 1.1 mmhos/cm or more (Butcher et al., 2016). Corn yields will be reduced by ten percent at EC levels of 2.0 mmhos/cm and about twenty percent at EC levels of slightly over 2.5 mmhos/cm (Butcher et al., 2015). So corn planting should be avoided at EC levels of 2.5 mmhos/cm or more. Canola yields started declining at EC levels of 0.5 mmhos/cm and twenty percent yield loss was observed at EC levels of 2.0 mmhos/cm. At EC of 3.0 mmohs/cm, nearly forty percent canola yield loss was recorded (Steppuhn and Raney, 2005). Sunflower showed a similar trend like canola (Katerji et al., 2000). So at EC levels of 2.0 mmhos/cm or more, both canola and sunflower would not be suitable crops unless significant yield losses are acceptable. Spring wheat showed twenty percent reduced yields at EC levels close to 3.0 mmhos/cm and thirty percent reduction at EC levels of 4.0 mmhos/cm (Thapa et al., 2016). Consequently, spring wheat, durum or winter wheat will not be suitable crops if the EC levels are 3.0 mmhos/cm or more.

The two most salt-tolerant annual crops are barley and oat. Canadian research showed that both barley and oat yields started declining at EC levels of 4.0 mmhos/cm or more (Fowler and Hamm, 1980). About twenty percent yield reductions were observed for barley at EC levels of 7.0 mmhos/cm and for oat at EC of 8.0 mmhos/cm. Once soil EC levels are 8.0 mmhos/cm or more, planting a mix of perennial salt-tolerant grasses will have the best chance to be established compared with any of the annual crops mentioned above, including barley and oat. Potential grasses include Tall Wheatgrass, Slender Wheatgrass, Western Wheatgrass and Russian Wildrye. Seeding rate for all four grasses will be eight pounds per acre or two pounds of each grass per acre.

Though all of these grasses are cool-season, they can be planted from May to August. Seeding with a drill is best, but broadcasting followed by harrowing has also produced good germination. Since they are perennial, they take about one to one and a half years to get established and about two years to suppress the weeds.

Planting the salt-tolerant perennial grasses on areas with an EC of 8.0 mmhos/cm or more have several advantages over the annual crops:

  • The mix of four grasses mentioned above have an EC tolerance of 6.0 to 26.0 mmhos/cm.
  • Since it will take several years for EC to lower to acceptable levels on areas with an EC of 8.0 mmhos/cm or more, perennial grasses will not need replanting and will save producers time and money.
  • These grasses will establish on high EC areas, reduce soil evaporation, use excess water and minimize wicking up of soil water, thereby salts.
  • With proper management (grazing, mowing or haying), roots for some of the grasses (like Western Wheatgrass) can go deeper than four to five-feet in three to four-years. That will help lower the groundwater depths, as well.
  • They can provide fair to good quality hay depending upon the timing of the harvest.
  • Some grasses establish early in the season and some late. In a mix, there will always be some green plants during the growing season.

Reference:

Butcher, K., C. Langseth, T. DeSutter, A. Wick, and J. Harmon. 2016. Soybean response to soil salinity. NDSU Ext. Ser. Soil Health and Land Management Circular. https://www.ndsu.edu/soilhealth/wp-content/uploads/2015/12/Soybean-Salinity_6-13-16.pdf (accessed April, 2019).

Thapa, R., A. Wick, A. Chatterjee, T. DeSutter, and C. Langseth. 2016. Spring wheat response to salinity. NDSU Ext. Cir. Soil Health and Land Management. https://www.ndsu.edu/soilhealth/wp-content/uploads/2015/12/wheat-salinity_6-13-16.pdf (Accessed February 2019).

Butcher, K., C. Heglund, T. DeSutter, A. Wick, and J. Harmon. 2015. Corn response to soil salinity. NDSU Ext. Ser. Soil Health and Land Management Circular. https://www.ndsu.edu/soilhealth/wp-content/uploads/2015/12/Corn-salinity_6-13-16.pdf (accessed February, 2019).

Brennan J. and M. Ulmer. 2010. Salinity in the Northern Great Plains, Natural Resources Conservation Service, Bismarck, N.D.

Steppuhn, H. and J.P. Raney. 2005. Emergence, height, and yield of canola and barley grown in saline root zones. Can. Plant Sci. 85:815-827.

Katerji, N., J.W. van Hoorn, A. Hamdy, and M. Mastrorilli. 2000. Salt tolerance classification of crops according to soil salinity and to water stress day index. Agric. Water Management 43:99-109.

Fowler, D.B., and J.W. Hamm. 1980. Crop response to saline soil conditions in the Parkland area of Saskatchewan. Can. J. Soil Sci. 60:439-449.

Naeem Kalwar

Extension Soil Health Specialist

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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