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Frozen soils: Life under the soil

More of our nutrients are lost of snow melt run-off than rain. Researchers are working 
on ways to lower this loss

Dr. Barbara Cade-Menun is a research scientist at the Semiarid Prairie Agricultural Research Centre (SPARC) at Swift Current, Saskatchewan. A soil scientist by training, Cade-Menum is the “nutrient cycling” scientist at SPARC. This role moves her beyond traditional soil fertility, and includes nutrient transport from land to water. The focus of her research is to understand how nutrients cycle and move, particularly phosphorus, and to minimize the impacts of agriculture on the environment, especially with respect to water quality.

Cade-Menun has been involved in the study of watersheds and their conservation and is part of a Canada-wide Agriculture and Agri-Food Canada (AAFC) funded study that looks at protecting and managing watersheds and preventing excessive nutrient run-off. The Saskatchewan project started in 2009, and is testing a number of management practices that may help reduce nutrient run-off during the spring snow melt. Her study area is close to Moosomin, in the Pipestone Creek watershed.

“On the Prairies, most of the nutrients get washed off in snow melt run-off, not in rain events as in other parts of Canada or the U.S.,” says Cade-Menun. “Here rain events occur when plants are actively growing and nutrient run-off is negligible.”

Many management practices have been developed to prevent run-off as a result of summer storms. “In the case of summer storms, particulate matter is eroded, which you can see as soil or mud moving in runoff water, for example,” according to Dr. Cade-Menun. “Snow melt is different. In that case, the nutrients are mainly dissolved in the melt water and it’s a lot harder to stop or prevent.”

If this project is successful in finding ways to reduce snow melt nutrient run-off, it will not only improve water quality but also reduce farmers’ costs by keeping nutrients on the land where they are needed.

Pasture

Restoring wetlands is one management practice that works particularly in the so-called Prairie Pothole Region of Saskatchewan, Manitoba and South and North Dakota. “These potholes are seasonal and show up as depressions that fill with melt water in the spring,” says Cade-Menun. “Generally farmers have to seed around these water-filled depressions in the spring, but by summer they dry out and show up as bare spots.”

Dr. Cade-Menun and her team are only looking at restoring wetlands on pasture. “Although the wetlands would be beneficial for croplands, too, cropland farmers find managing around these seasonal potholes too time-consuming, as well as creating other potential weedy issues later in the season. In many cases, seasonal potholes have already been drained on croplands.”

Another management strategy under study on pasture is infield winter bale grazing. Leaving the bales out on the pasture with the cattle is considered beneficial. The cattle would only be brought in if there is extreme weather. There are some savings: bales don’t have to be hauled in, manure does not have to be spread out of corrals after winter and cattle are healthier, not having been clustered together all winter. “In this case, we are really comparing nutrient run-off in the infield grazing situation to the situation where manure is spread in the fall against a summer-grazed pasture,” explains Dr. Cade-Menun. “In both cases — bale-grazing and manure-spreading — we see increased nutrient run-off versus a summer-grazed pasture. Although we have more work to do, we can say that farmers have to be careful where they graze cattle and where they spread manure. If the run-off stays on the land, the pastures will benefit from the nutrients in the runoff. If the run-off is likely to contaminate a domestic water source, a river, stream or lake, then that’s obviously not a good scenario.”

Cropland management

Turning to croplands, the team is looking at two management strategies. The first is a nutrient reduction strategy that has farmers getting fertilizer recommendations based on soil tests.

“Instead of applying all this fertilizer at once, we are having the farmer reduce the recommended amount by one-third,” says Dr. Cade-Menun. “If the crop progresses well and conditions are favourable, a top-dressing can be applied in-crop. However, we haven’t needed to do that yet, mostly due to the weather conditions of the past few years.”

The results of this trial are just being analyzed now as the site was not seeded in 2011 due to flooding. “This is a good example of why multi-year experiments are so necessary in agriculture,” explains Dr. Cade-Menun. “If we only looked at 2011, we would say it never stops raining in Saskatchewan and we should be growing rice. Well, maybe that’s a bit of a stretch, but it does go to demonstrate we can’t ever rely on just one year of data.”

The second cropland management practice under evaluation involves seeding marginal land with salinity issues to perennial forage — a blend of alfalfa, tall fescue, slender wheatgrass and tall wheatgrass. This may cut down on nutrient losses, compared to seeding fertilized crops that don’t grow well due to salinity.

“There’s no guarantee that this will reduce nutrient losses,” says Dr. Cade-Menun. “A pasture is still living when it freezes compared to cropland where the crop is matured and removed. The pasture is still releasing nutrients.” This trial was seeded in 2011 and the results are still being analysed. It will be studied for another two years.

This is a very complex area of study. Cropland and pastures both release nutrients, in similar concentrations but in different forms. For instance, in the case of nitrogen, croplands release more organic nitrogen; pasture releases more dissolved ammonia.

Then there is the weather to contend with, and the multitude of other variables come into play. It’s also important to understand the cost-benefits of the different practises. In order to try and cover all these different areas that impact this study, Dr. Cade-Menun and her team work cooperatively with the University of Regina, Saskatchewan Water Security Agency, Lower Souris Watershed Committee, the University of Alberta and others.

“Our community of scientists involved in this work wants to come up with some management strategies, easily adopted by farmers, that can mitigate against nutrient loss in snowmelt runoff in most situations, keeping those nutrients in the fields where they can be used by producers” says Dr. Cade-Menun.

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