White-crusted, salty, saline soils have plagued agriculture for thousands of years, and even contributed to the downfall of civilizations. While Prairie agriculture isn’t teetering on the brink of collapse because of salinity like the fall of the ancient Mesopotamia, salinity is an ongoing concern for some Prairie farmers. Estimates put about nine per cent of Prairie agricultural land at moderate, high or very high risk of salinization.

“Can we get something to grow? With the new emphasis on carbon sequestration, what is the nature and impact on carbon storage in these soils?” asks Jeff Schoenau, soil scientist with the College of Agriculture and Bioresources at the University of Saskatchewan (USask) in Saskatoon, Sask.

In semi-arid regions on the Prairies, salinity occurs when subsurface ground water moves upward in the soil profile, carrying naturally occurring salts to the surface. These salts typically include calcium (Ca), magnesium, sulphates and chlorides. Salinity is measured by electrical conductivity (EC) in decisiemens per square metre (dS/m). Soils less than 2 dS/m are classified as non-saline, 2 to 4 dS/m as slightly saline with sensitive crops affected, 4 to 8 dS/m as moderately saline with most crop growth affected, and above 8 dS/m as severely saline with only tolerant plants surviving.

AC Saltlander establishment on non-saline site June 2018 one year after seeding.

Schoenau led a research study that started in 2017 to see if a moderately saline site could be brought back to productivity using AC Saltlander green wheatgrass alone or with three added organic amendments. The objectives were to assess wheatgrass yield and nutrition over six years, and how soil salinity and soil organic carbon were affected by the establishment of AC Saltlander with organic amendments.

The research was conducted in the Brown soil zone near Central Butte, Sask. on both non-saline and saline locations in the field. The non-saline site plots had an EC ranging from 0.297 to 0.315 dS/m in the 0- to 24-in (0 to 60 cm) soil profile. The saline site was rated as moderately saline with an EC of 6.29 to 6.75 dS/m in the 0- to 24-in profile. Soil organic carbon was similar between the two sites, ranging from 0.93 to 1.47 per cent. Soil pH was slightly above 7.0.

“The available nutrients were higher at the saline site because of reduced crop removal from poor crop growth over the years. Soil organic carbon was similar because native salt-tolerant vegetation, followed by foxtail barley and kochia growth after cultivation, likely helped maintain the organic matter in the soil,” says Schoenau.

Organic amendment treatments included leonardite at 8,921 lb/ac (10,000 kg/ha), humic acid at 178 lb/ac (200 kg/ha) and composted manure at 8,921 lb/ac (10,000 kg/ha), along with an untreated control. Leonardite is a soft, oxidized lignite coal rich in humic acids. The treatments were applied in the spring of 2017, followed by seeding of AC Saltlander into the amended treatments.

All sites received a blanket application of 45 lb nitrogen (N)/ac (50 kg N/ha), and 18 lb P₂O₅/ac (20 kg/ha) prior to treatment.

Stand establishment of AC Saltlander was much better on the non-saline site than the saline site. Similarly, forage yield was much higher in the first year in the fall of 2017 at around 4,460 lb/ac (5,000 kg/ha) on the non-saline site compared to about 892 lb/ac (1,000 kg/ha) on the saline site. At both sites, the organic amendments had no impact on forage yield.

Nutrient uptake was measured for N, phosphorus (P), sodium (Na) and Ca in the fall of 2017. Uptake of all nutrients was much higher in the non-saline plots because of the higher yield. The organic amendment treatments did not have an impact on nutrient uptake in either the saline or the non-saline plots.
In the spring of 2018, the leonardite treatment had slightly higher soil organic carbon mass at both the non-saline and saline site. However, in the saline site, it was also statistically similar to the composted manure treatment.

Soil pH and EC was measured in the fall of 2018, and the organic amendment treatments had no significant effect on either soil parameter.

By the fall of 2019, yield on the two sites was almost the same. The fall biomass yield on the non-saline site was 2,466 lb/ac +/- 565 lb (2,765 kg/ha +/- 633 kg). The saline site yield was 2,331 lb/ac +/- 925 lb (2,613 kg/ha +/- 1036 kg/ha).

“Difference in forage growth on non-saline and saline soils was diminishing in subsequent years. The green wheatgrass was catching up on the saline site. Roots of salt-tolerant grass, once established, can use shallow ground water and residual nutrients,” says Schoenau. “We were getting a palatable forage to grow well on salt-affected land.”

Saline site became more productive
Even more encouraging, by August 2022, the forage biomass yield on the saline site had surpassed the non-saline site. The saline site yield was 3,220 lb/ac +/- 525 lb (3,609 kg/ha +/- 588 kg) compared to 2,200 lb/ac +/- 503 lb (2,466 kg/ha +/- 564 kg) on the non-saline site.

There was a trend for the soil amendments to increase yield, but it was not consistent or statistically significant. The addition of leonardite significantly increased total soil organic carbon mass in the top 6 in (15 cm) because it is resistant to decomposition. Removal of the Ca, Mg and Na salt cations in the forage harvest was negligible compared to the total amount of salts in the profile.

After six years, root biomass was significantly higher in both the saline and non-saline sites compared to adjacent spring wheat crops. This was explained by greater root mass produced in the AC Saltlander green wheatgrass plots compared to the annual wheat crop.

“Overall surface soil salinity was lower in 2023 than in 2017, and that may partly reflect the grass helping to lower the water table,” says Schoenau.

Schoenau has plans for several follow-up studies. One is looking at a salt-tolerant alfalfa/wheatgrass mix from Bill Bilegetu’s forage development program at the USask’s Crop Development Centre. A second is looking at the termination of the AC Saltlander plots and seeding back to an annual crop with yield and soil properties monitored for the following two years.

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