Fertility and Nutrients
Getting something to grow
By Bruce Barker
Investigating organic amendments on saline soils to improve AC Saltlander production.
When AC Saltlander green wheatgrass was released in 2006, farmers had a new tool to use on saline soils. Its salinity tolerance was comparable to tall wheatgrass and forage quality comparable to smooth brome grass. Now, researchers are trying to improve the performance of AC Saltlander through the addition of organic amendments to the soil.
“Unproductive salt-affected areas continue to persist and expand on the Prairies while the demand for arable land continues to grow,” says soil scientist Jeff Schoenau at the University of Saskatchewan. “Getting something of value to grow on these saline areas can help manage the problem.”
AC Saltlander is a hybrid between Eurasian bluebunch, wheatgrass and quackgrass collected from Turkey. It is the result of collaboration between Agriculture and Agri-Food Canada at Swift Current and the United States Department of Agriculture. While successful in its own right, Schoenau and graduate student Paul Hrycyk wanted to see if adding leonardite, humic acid or composted steer manure could improve AC Saltlander yield and nutrition, and what effect these amendments had on soil organic carbon and salinity.
Leonardite is the overburden found above coal deposits. Humic acid is an organic compound that, in this case, was derived from leonardite.
The research was conducted on a field in central Saskatchewan that included saline and non-saline plots. Salinity was rated moderate to severe with an EC of 6.32 in the top six inches (15 centimetres) of soil compared to 0.32 on the non-saline soil. Organic matter was similar between the saline and non-saline sites.
“The saline area had higher levels of N, P, K and S because it hadn’t produced much crop but had still been fertilized for many years,” Schoenau says.
Total soil organic carbon was similar in the two sites. Native salt-tolerant vegetation, along with invasive foxtail barley and kochia following cultivation likely helped maintain soil organic carbon on the saline site.
“I was surprised at first, but some weeds had grown there for a lot of years. Foxtail barley has a dense rooting system, so maybe there was some significant below ground carbon addition over the years,” Schoenau says.
Field pea was grown the year prior to the establishment of the plots in the spring of 2017. The sites received a blanket application of 45 lbs. N per acre (50 kg N/ha) and 18 lbs. P2O5 per acre (20 kg P2O5 /ha).
In the spring of 2017, leonardite was applied at 4.46 tons per acre (10 tonne/ha); humic acid was applied at 0.89 ton per acre (0.2 tonnes/ha); and composted manure was applied at 4.46 tons per acre. These rates were applied to the saline and non-saline plots, and compared to a control with no organic amendment.
The rates for the solid amendments, leonardite and compost, were selected based on recommended application rate of solid manure for the region (10 tonnes/ha). These treatments were broadcast and incorporated. The liquid humic acid rate was selected based on normal fertilizer product application rate (200 kg/ha) and was seed-row placed.
AC Saltlander was seeded at 8.9 pounds per acre (10 kg/ha) on 10 inch (25 cm) row spacing on May 11, 2017.
No yield improvement with organic amendments
Yield of AC Saltlander differed greatly in the fall of 2017 between the saline and non-saline areas. In the plots without amendments, yield was about 2.23 tons per acre (five tonnes/ha) on the non-saline plots compared to 0.446 tons per acre (one tonne/ha) on the saline site – five times higher yield on the non-saline site. The organic amendments did not significantly differ from the control treatment on either the saline or non-saline sites.
In the spring of 2018, yield on the saline sites was catching up, and was about one-half of the non-saline site. Schoenau says there was a trend for the organic amendments to increase yield on both sites, but it was not statistically significant.
The fall 2019 yield was impacted by a very dry spring. Yields were statistically similar between the non-saline and saline sites, but with large variability. On the non-saline site, yield was 1.23 tons per acre (2.765 tonnes/ha), and 1.16 tons per acre (2.613 tonnes/ha) on the saline site. Again, there was no significant benefit derived from the organic amendments.
Nutrient uptake was also measured in above-ground biomass of AC Saltlander. Schoenau says there were no differences in uptake of N, P, Na and Ca between organic amendment treatments, or between saline and non-saline soils. “There was pretty negligible uptake of the Ca and Na salt cations.”
Leonardite significantly improved soil organic carbon compared to the other amendments and the control, on both sites by the spring of 2018. Schoenau explains that leonardite is slow to decompose, resulting in higher soil organic carbon in the top four inches (10 cm) of the soil.
The organic amendments did not significantly change pH or EC values in the 24 inch (60 cm) depth.
Masters student Gravel Wang is carrying on the research for another two years in 2020 and 2021. A new site was added in 2020 at Clavet, Sask., with salt-tolerant alfalfa alone and in a mix with grass, and added organic amendment treatments. Isotopes will be used to compare the relative contribution that groundwater makes versus rainfall to the overall water used by the forage species in the saline and non-saline sites. It is suspected that salt-tolerant forages can make good use of shallow groundwater and accumulated nutrients in the salt affected areas of the field.
“What we’ve found so far is that getting a palatable forage established with roots down to water table is making salt-affected land productive again,” Schoenau says. “Seeding areas to salt-tolerant wheatgrass and applying a large amount of a high carbon content amendment like leonardite are two approaches to increase the soil organic carbon over a short time period.”