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Largest Soil Study in Canada Shows Simple Yet Profound Discovery

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Media Relations
Agriculture and Agri-Food Canada
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One of the largest soil studies ever to take place in Canada has produced an important discovery – that litter decomposition in soil is driven mainly by temperature, even in very different soils and places.

This finding may appear simple, but the implications are profound in the face of climate change.  As global atmospheric temperatures rise, so will soil temperatures.  Warmer soils will decompose organic matter faster.  This could change nutrient cycling and carbon storage in soils and raise the need for new agricultural practices.

Soil scientists with Agriculture and Agri-Food Canada (AAFC) have already been working on this long-term study for 10 years.  This massive study spans 3,500 kilometres and 10 research sites at different locations across the country.

Soils are a fascinating assemblage of mineral particles, organic debris, living organisms, air, and water.  Intricate interwoven processes happen here, all of them critical to producing the food we eat.  One of these processes – decomposition – breaks down crop leaves, stems, and roots that are left behind after harvesting. This breakdown of organic materials back into their components replenishes the soil with the nutrients that new plants need to grow.  It also releases some carbon as carbon dioxide into the atmosphere, and converts other carbon into stable forms that the soil can store.

Researchers in this study wanted to understand litter decay better in various agricultural zones across Canada.  Dr. Ed Gregorich, AAFC's principal researcher on the project, explains:

"To conduct this experiment, we need to be able to track where carbon is in the soil.  We do this by growing barley in greenhouse chambers that receive carbon dioxide containing a carbon isotope, which is a heavier-than-usual type of carbon atom called carbon-13.  The barley takes this carbon dioxide in during photosynthesis and incorporates the carbon-13 into its tissues. Then we harvest the barley and apply the straw to the study soils as litter. As the straw decomposes, we can track the carbon-13 it contained as it moves into and through the soil."

After five years of monitoring the rate of litter decay and looking at all the variables, the researchers determined that one factor dictated the decay rate – temperature.  This means that any change in annual temperatures could affect how fast nutrients are replaced in the soil and how long carbon can be stored in the soil.

"By using our computer model, we see that litter is expected to decay two years faster if global temperatures rise by the predicted 2 degrees Celsius over the next 50 years," says Dr. Gregorich.  "This could have a significant impact on when and how much fertilizer is used or how much carbon can be stored in the soil and for how long."

This study has already increased our understanding of soils and decomposition, but many more questions remain.  The hope is that this long-term study will continue to uncover many of the secrets hiding under our feet. The study has now expanded internationally to include sites ranging from the Canadian Arctic in the north to New Zealand in the south.

Key discoveries (benefits)

Photo Gallery

Pots of barley plants growing in a glass chamber inside a greenhouse.
Chamber used to grow barley to receive a tracer in carbon dioxide called carbon-13.
Two rows of over 80 plastic tubes inserted vertically into a field
Study site showing tubes where the straw was added to the soil

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