Reducing run-off and improving soil health are the best path to address flooding and excess nutrients, according to a University of Manitoba expert on watershed management.
These strategies include more collection of surface water before it leaves the farm and adoption of soil management practices that build soil structure and help water infiltrate, says David Lobb, senior research chair with the Watershed Systems Research Program at the University of Manitoba.
The program, part of the agriculture faculty’s department of soil science, has overseen a wide range of studies exploring and testing integrated approaches to water management. Their work includes identifying environmental and socio-economic benefits of various farm practices that help both reduce the risk of flooding and protect the quality of surface water.
Lobb recently shared a list of best practices that have emerged from these multiple studies, which could benefit both farmers and the environment.
Collecting surface water before it leaves the farm ranks near the top of that list.
That requires retaining more wetlands in Manitoba’s pothole country and the use of small dams in regions along the escarpment. In the flat country of the Red River Valley it would mean construction of more on-farm ponds into which water flooding the farm could be directed, held, used as required, with the excess released.
Collecting surface water would help address one of agriculture’s biggest problems, which is area flooding, said Lobb.
This is the gradual buildup of water on farmland every year resulting from existing drainage systems he says he’ll “politely refer to as suboptimal.”
He calls the loss of productivity from flooded farmland occurring each year “the biggest limitation to agriculture in this province.” And it’s not getting nearly the attention it needs, he said.
“This is a massive economic problem for agriculture that is largely ignored,” he said. “It is probably the biggest limitation to agriculture in this province.”
Meanwhile, studies show collecting and holding water not only gives farmers more control over drainage, but also controls run-off, therefore reducing the phosphorus loading downstream.
“Some have suggested we allow agricultural land to flood. The problem is when you flood ag land it releases phosphorus and the load downstream becomes elevated,” he said.
However, it’s not just fertilized cropland releasing phosphorus, and that’s actually the crux of the matter.
Phosphorus comes off all rural land and that also includes municipal practices such as dumping effluent into streams, and the presence of natural vegetation including riparian vegetation on the landscape he said.
“It’s all releasing phosphorus,” he said. “It’s not so easy to link it to agricultural practices.”
That’s where other practices such as better designed and maintained surface drains, play a role, he said.
“Not an insignificant quantity of nutrients” move downstream produced by all the vegetation contained in this province’s thousands of km of roadside ditches, Lobb said.
“Massive vegetation in these ditches is also a problem for the original design to convey water,” he said.
“And just mowed down and left, it becomes a nutrient source.”
Another BMP on the list calls for enhancement of subsurface drainage.
Yes, it’s admittedly controversial to talk about tile drainage as part of the solution, Lobb said, but this isn’t about using tile to send more water downstream.
“It’s to encourage drainage to go into the collection ponds.”
Other farm practices include enhancing infield waterways and edge-of-field waterways, using landforms to slow surface run-off.
However, topping the BMP list is the use of low-disturbance field equipment, a practice that both improves soil structure and enhances soil health.
“This is something we don’t spend enough time talking about,” Lobb said.
Healthy soil with high levels of organic matter and biological activity increases infiltration and interception of water, allowing soil to store water rather than wash over it.
Soil conservation practices and nutrient management practices are important, but when it comes to reducing run-off they don’t really have an impact, he said.
“Soil conservation practices as we know them currently increase residues on the soil surface and they can also result in a tremendous amount of soil disturbance,” he said. “You may have soil conservation practices which increase tillage erosion which is bad and actually increase nutrient losses.
“Focusing on run-off is the most efficient way to deal with water quality problems, flooding and eutrophication.”