Manure slipping through cracks
At the onset of the experiment, a pesticide sprayer is used to apply blue-dyed water on top of a 1m by 1m soil plot. Credit: Genevieve Aliresearc
Researchers from the University of Manitoba, Canada, have found that water infiltrates deeper into cracking clay, vertisolic soils, when liquid hog manure is applied. The findings of the study give insights into how excess nutrients from fields travel through soil.,
The study also showed that even though water infiltration went deeper in the presence of manure, it did not reach depths of 1m.That's how deep tile drain, designed to remove excess subsurface water, are typically installed in the study region.
‘This observation challenges previous studies, which showed that cracks in clay soils can promote the travel of water and associated contaminants from the soil surface into tile drains,’ said Genevieve Ali, a researcher at the University of Manitoba. ‘Our study suggests that not all clay-rich soils behave the same.’
The researchers focused on vertisols because they are present in large regions of North America. ‘They are common in agricultural plains, where excess nutrients may be common due to intensive farming,’ said Ali.
Follow the water
Water can flow through soil in different ways. Matrix flow occurs when water moves slowly through tiny spaces between soil grains. Preferential flow takes place when water travels relatively quickly through bigger channels, called macropores, such as cracks and earthworm burrows.
Macropores are often connected to one another. ‘They act like a network of pipes, and they can be created or exacerbated by human activities,’ said Ali. ‘Knowing when and where there is preferential flow and how to manage land in those areas is critical to preserving groundwater quality.’
Clay-rich soils, such as vertisols, tend to crack, which creates macropores. ‘That makes these soils natural candidates to study the relative importance of matrix and preferential flow,’ said Ali.
This study was conducted in research plots in Manitoba, Canada. Researchers added liquid hog manure to one plot but not the other. They sprinkled water mixed with blue dye on both plots to determine how water moved through the soil.
In the plot where manure was applied, water reached up to 64 cm into the soil. In contrast, water reached up to 45 cm in the plot where manure was not applied. Both plots showed evidence of matrix and preferential water flow.
More research needed
This study focused on a single site, so Ali said that further research is needed before generalisations can be made.
Read more about this research in Agricultural and Environmental Letters.
