Frozen Soils – Life goes on under the snow

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Earlier this year The Canadian Journal of Soil Science published a special edition about the effects of winter on soil. Two Saskatchewan-based AAFC research papers were featured.

“The unique aspects of the Canadian agricultural landscape gave rise to this special edition,” notes Dr. Barbara Cade-Menun, lead author of one of the papers and co-editor of this edition of the Journal. “Typically, American studies focus on rainfall runoff events, but rainstorms play a much less significant role here. The Prairies are unique in the importance freezing and snowmelt runoff plays.”

A key difference between rainfall- and snowmelt-caused nutrient movement is that rainfall causes erosion – particles move. Studies show that these particles can be stopped with buffers or other physical methods. Snowmelt runoff is a different story: the majority of nutrients are dissolved, which means new methods of stopping this movement must be investigated.

Why does this matter to producers? This research could impact producers’ decisions during the growing and harvest seasons. Specific management practices, particularly in the fall, may be required to control gas and nutrient losses during winter and at snowmelt.

“Lots of life goes on under the snow,” says Barbara Cade-Menun. “Soil processes don’t stop during the winter – things go on under snow, during freeze-thaw cycles in fall, winter and spring, and during spring snowmelt.”

Nutrient Loss from Snowmelt Runoff

This research project, led by Dr. Cade-Menun, looks at nutrient loss (including phosphorus, carbon, potassium and sulfur) from cropland and pasture in spring snowmelt runoff near Moosomin.

“We’re investigating what we can do to minimize nutrient loss,” says Dr. Cade-Menun. “We want to retain nutrients where they can do the most good – both to reduce costs to farmers and to address concerns about water quality.”

The results of this preliminary study show that nutrients are lost from both annual cropland (zero till) and perennial tame pastures during snowmelt runoff, often in concentrations exceeding water quality guidelines. What is different between the two cropping systems is the physical and chemical forms these exported nutrients take.

Nutrient-specific best management practices are required to control nutrient loss from different cropping systems. While this preliminary study highlights that point, work is ongoing to determine which management practices work best – from wetland restoration to forage and grazing possibilities.

Freeze-Thaw Cycles

A second study led from the Semiarid Prairie Agricultural Research Centre (SPARC) in Swift Current focuses on freeze-thaw cycles and soil water content effects on the rate at which soil is able to absorb precipitation and snowmelt. Three southwest Saskatchewan soils, all taken from within 50 kilometres of Swift Current, were studied: Hatton loamy sand (sampled near Cabri), Swinton loam (from south of SPARC ) and Sceptre clay (from near Stewart Valley).

Recent predictions of more unstable winter temperatures and reduced snow cover may result in an increased frequency of freeze-thaw cycles. In turn, increased freeze-thaw cycles cause changes in soil physical properties and affect water movement in the landscape, which may affect ecosystem diversity and productivity.

This study, led by former SPARC postdoctoral fellow Dr. Ymène Fouli, found that soil texture and soil moisture prior to freezing had a significant effect on the rate at which soil absorbs moisture. Depending on both of these factors, freeze-thaw cycles either maintained, increased, or lowered the rate at which the soil was able to absorb precipitation.

Given the variability of soil texture and water content on the Prairies and the potential for increased soil changes in the future, understanding freeze-thaw cycles is an important part of scientists’ knowledge of the environmental impact of agricultural and other practices.

This research benefits farmers by identifying variability in how water moves in the soil landscape following freeze-thaw cycles and could lead to future improvements in farming productivity and sustainability through improved water management.

Organizations: Canadian Journal of Soil Science, Semiarid Prairie Agricultural Research Centre

Geographic location: Swift Current, Moosomin, Saskatchewan Cabri Stewart Valley

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