Cover crops’ effects on water runoff and greenhouse gas emissions were among projects seen by visitors to the University of Guelph’s Soils@Guelph research plots.
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In late September, the Soils@Guelph team of multi-disciplinary collaborators hosted a research day at the university’s Elora Research Station farm. Soils@Guelph, established following a 2018 private donation and subsequently supported financially through the provincial agriculture department and other partnerships, enables knowledge sharing between researchers, farmers, industry, government and the public.
One project highlighted at the research day, originated from the School of Environmental Sciences, compares water movement in the subsurface of plots with a no-tilled corn-soybeans-wheat rotation, with or without cover crops. Another replication of the same study aims to mimic a compacted soil under no-till management and the same crop rotation.
A series of rectangular plots at the edge of a field were subjected to a simulated 40 millimetre rain event.
“That’s a fairly intense rainfall event that isn’t all that common,” admitted Masters student Jack Moore, but the goal was to evenly distribute that amount of rainfall across the entire research area.
Blue food dye was added to the water. A pit was then dug at each location and the team used image processing software to analyze photos of the soil profile to determine water movement.
Moore said there are two types of flow in the soil: matrix flow, which is the uniform spread of water in every direction; and preferential flow, which occurs when water finds paths of least resistance to flow in an uneven manner to different parts of the soil profile.
Preferential flow is how water typically reaches greater depths in some locations, due to root channels, earthworm burrows and other permeable materials.
Nutrients can become unavailable more quickly to plants due to preferential flow, he said, and water can run off quicker if the path of least resistance leads across the surface.
Results indicate no significant difference in preferential flow in plots with cover crops compared to those without cover crops.
At another corn-soybeans-wheat location, where part of the field has had cover crops in the rotation since 2018, researchers are monitoring 20 litres per minute of air emitted from the soil to assess potential greenhouse gas implications of different crop management regimes.
Results indicate more nitrous oxide emissions but fewer carbon dioxide emissions from the cover crop site. Soil moisture and temperature are more stable in the cover crop site.
Connor Goodwin, a Master’s student in professor Kim Schneider’s plant agriculture lab, is wrapping up his third year of trials looking at legume cover crops as a source of nitrogen for a subsequent corn crop.
Red clover is frost-seeded on some of the plots and the others — some only legumes, others with legumes in a more complex mix — are planted in the fall, after harvest of the previous crop.
The highest yielding of the crops tried so far was red clover in 2021, with the bountiful cover crop providing 80 kilograms of N per hectare for the next year’s corn crop. Goodwin said that translates into an extra $15 income per hectare from the field, without factoring in the long-term benefits to the soil.
It was very dry in 2022, however, and the red clover did not perform well. In contrast, the most stable cover crop in terms of yield and performance over three years was an oats/pea/radish mixture. Even in the dry year, there was good establishment with this mix.
Goodwin has also been looking at the forage potential of cover crops. Being able to harvest the crop for feed could offer a secondary incentive — aside from building soil health — for growing cover crops.
He determined there’s a 13 kg of N per hectare penalty with the oats/pea mixture if it’s harvested for forage. This translates into a yield decrease in the following year’s corn from 8.65 tonnes per hectare to eight tonnes per hectare.
A different study, also through professor Schneider’s lab, was presented during the Beef@Guelph research evening that followed the Soils@Guelph event. It is exploring the agronomic potential of different annual forages for either extending the grazing season or supplementing grazing during a dry summer period.
In the second year of a two-year rotation, researchers are growing plots of various crops ranging from fall rye and fall triticale to an oats/peas mix and a diverse mix including millet and sorghum Sudan grass.
The winter cereals are grazed in the spring and the warm season crops are grazed two times over the summer.
Four separate groups of cattle are rotationally grazed through the plots, allowing for four replications of the trial.