Soil organic matter (SOM) is the fraction of soil that is comprised of plant and animal tissues decomposed to varying degrees, and is critical to soil health.
It contributes to an array of important soil properties and processes including water infiltration, soil aeration, water holding capacity, nutrient cycling, and suppression of diseases and pests.
Soil organic matter is one of the most important soil properties for supporting healthy crops.
Of concern to agriculture in the Fraser Valley, including Delta, is significant declines in SOM that have been observed over the last three decades.
These declines in SOM were recently identified in an analysis that was part of our five-year research project in partnership with the University of British Columbia (UBC) that assessed the impact of grassland set-asides on various soil properties and crop yields.
One component of the study included an investigation across the Fraser Valley for changes in soil organic carbon (SOC) conducted by Dr. Siddhartho Paul (http://sal-lab.landfood.ubc.ca/)
Soil organic carbon is an indicator of soil quality and is a measure of SOM.
Study results showed sharp declines in SOC in some areas across the Fraser Valley.
Across the agricultural landscape of Delta, 93% of the area experienced a decline in SOM from 1984 to 2018.
For annual cropped fields, mean SOC declined by roughly 42% over the three decades with current median SOC equal to 23.14 g C/kg soil (2.3%).
Declining SOM is important to address and will become even more important as extreme weather becomes more common due to climate change in the years ahead.
Commonly used practices to increase SOM include incorporating crop residues, animal manure and compost; planting of cover crops; crop rotations particularly including perennial grasses and legumes; and reductions in tillage practices.
The Delta Farmland and Wildlife Trust supports many of these practices through our stewardship programs.
Further research is currently being conducted by UBC to assess how practices such as winter cover crops and grassland set-asides impact SOM.
This article was originally published in the DFWT’s Winter 2021 newsletter and was contributed to the Delta Optimist.