Producers can increase field crop yields and reduce soil and environmental damage with management practices suitable for all soil types, says Dan Reynolds, research scientist at Agriculture and Agri-Food Canada's (AAFC) Harrow Research and Development Centre in Ontario.
"Long multi-crop rotations, which include perennials, seem to improve soil attributes," he says. The combination of rotating crops, adding amendments and planting cover crops in the fall can improve the physical quality and resilience of soil.
Although soil types are the primary determinant of physical quality and resilience, good management practices can improve and maintain the capacities of virtually any soil, says Reynolds. On the other hand, over-cultivation and long-term use of monocultures or two-crop rotations will eventually degrade any soil.
In collaboration with the Ontario Soil and Crop Improvement Association (OSCIA), Reynolds and his team examined soil physical quality and resilience in two studies.
In the first study, in 2013, soil physical quality was tested at 10 field sites across southern Ontario with support from the Water Resource Adaptation and Management Initiative under Growing Forward, a federal-provincial-territorial initiative. Eighty intact soil core samples were collected and assessed for air capacity, plant-available water capacity, organic carbon content, and dry bulk density.
These physical capacities indicate a soil's ability to store root-essential air and water, the amount of organic matter sequestered in the soil, and soil hardness or compaction. It was found that physical quality was strongly affected by soil type (i.e., sandy, loamy, clayey), with loams having the best overall quality.
Of the 10 soils tested, "all had insufficient organic carbon and excess bulk density for optimal field crop production," notes Reynolds.
A second study in 2014, funded through Growing Forward 2, involved weekly field measurements of soil water content to assess soil resilience to heavy rains and drought conditions. Crops grown on a loam soil were highly resilient to water excesses and deficits because of a high capacity for storing plant-available air and water, exceeding 20% and 24% respectively. By contrast, a silty clay loam had low resilience to water excesses and deficits; this soil's capacities for storing air and water were only about 7% and 16% respectively.
"Both coarse- and fine-textured soils tend to have lower physical quality and lower resilience than medium-textured soils," Reynolds says. Medium-textured loams often have the best combination of air and water capacity for field crop production.
"Decades of field, laboratory and greenhouse research have established that a soil's plant-available air and water capacities should exceed 20% for maximum resilience to water excesses and deficits," he says.
Occasional analysis of soil core samples and periodic monitoring of soil water content in the crop root zone can help producers determine overall physical quality and resilience of soils, and detect stress. This can help optimize irrigation for high-value horticultural crops.
Use of cover crops may be another management practice for improving soil, and Reynolds and his team are currently studying this approach.