By Melisa Luymes
On March 29, over a hundred farmers from the Northern Bruce Peninsula met in Bill Ceaser’s new shed near Lion’s Head for a day about drainage and drones, aptly named D-Day. Organized by the Bruce Peninsula Biosphere Association (BPBA), the event also highlighted some of the work that the BPBA has been doing on phosphorus reduction structures.
The Peninsula has long been cattle country, but that is changing. Overtop a limestone karst system, many areas are shallow to bedrock and remain in trees and pastures. But there are a few thousand acres of historic floodplain and swamp that were drained for agriculture a century ago. This soil is deep, rich and, more recently, it has been bought by grain farmers from the south.
There are three main water systems in Northern Bruce Peninsula (NBP), the largest one being Judges Creek. As it crosses the Ferndale flats, the drain has very little slope and it is prone to extensive flooding after a rain, even during summer months. As Peninsula grain farmers are investing in drainage for their fields, they are dependent on old municipal drainage systems for outlet and have been struggling with the municipality for solutions to their flooding concerns. As drainage improvements can be quite costly and are charged to all landowners within the watershed area, drainage is now a hot topic on the Peninsula.
So, it was fitting that D-Day began with a presentation by NBP’s drainage superintendent, Stephen Cobean, P.Eng. of Cobide Engineering in Hanover. He outlined Ontario’s Drainage Act and the history of the municipal drains on the Peninsula. Under the Act, these drains are municipal infrastructure with a right-of-way easement across private property. Farmers may be tempted to bring an excavator back to the drain to do a cleanout themselves, but modifications to the ditch bottom could have major issues up or downstream. He explained that maintenance and improvements are done by the municipality on a complaint-driven basis and the complaints need to be filed in writing.
Brent Weigel spoke next about how drainage works and why it is an important investment for farmers. He runs Weigel Drainage Inc. and has been doing much of the drainage work on the Peninsula. Weigel began his presentation describing how drainage systems work to lower the water table by 2-3 feet and allow for air in the soil to promote deeper crop root development. Drainage also allows for farmers to get equipment onto a field sooner in the spring or after a rain. According to research, even a day or two earlier for planting can make a big increase in yields.
Next up, I spoke about some of the trade-offs of drainage and introduced controlled drainage as a potential innovation for the Peninsula. Drainage has come under scrutiny as being a contributor to Lake Erie phosphorus loading and I discussed the concerns with nutrients and drainage system in more detail, concluding with opportunities for water quality improvement within drainage systems.
To begin, phosphorus and nitrogen are very different nutrients, but they are both only valuable to a plant when they are dissolved in water and both are a concern when they get into rivers, groundwater or lakes. There is no denying that tile drainage systems are a transport pathway for soluble nutrients in the soil, but blaming tile drainage is like blaming the exhaust for pollution from cars on the roads. They are merely the pathway.
Both nitrogen (N) and phosphorus (P) have two main ways that they are lost in the environment. Simply put, nitrogen is either gassy or leaky and phosphorus is either sticky or leaky. The most cost-effective way to reduce both N and P loss is to avoid it in the first place by using 4R Nutrient Stewardship principles and applying the right fertilizers and manures at the right rate, the right time and the right place. Nutrient loss can also be avoided by keeping living roots in the soil to uptake the liquid nutrients instead.
Denitrification (gassy nitrogen) occurs in wet soils and makes a greenhouse gas (nitrous oxide) that is more potent than carbon dioxide. The best way to reduce denitrification is through drainage. According to Dr. Mike Castellano’s presentation at this past year’s Ontario Ag Conference, tile drainage reduces nitrogen off-gassing by about half. Furthermore, drier soils require less nitrogen for optimum yields and Castellano’s research at Iowa State University indicated that the optimal agronomic rate of nitrogen was 87 lb/ac less on corn (after corn) on a drained field, reducing the energy costs to make and transport that N in the first place.
Phosphorus, on the other hand, is sticky and binds to soil, so any avoidance of soil erosion is avoiding phosphorus loss. Again, tile drainage is one of the best ways to mitigate soil erosion because it allows for greater infiltration rates into the soil, so water doesn’t run across the surface as easily. Dr. Merrin Macrae’s research at the University of Waterloo has shown higher concentrations of the “sticky” phosphorus in surface water than in tile water, though soil type and slope determine by just how much. Other ways to reduce soil erosion are to minimize tillage, grow cover crops or install erosion-control berms and blind inlets to bring surface water safely into the subsurface tile system.
However, both nitrogen and phosphorus have a leaky component and can leave a field as dissolved nutrients, and this is the concern with drainage systems being a pathway. Total nutrient ‘loading’ is calculated by multiplying the concentration of nutrients in water by the flow rate of the water. So, that means there are two ways to reduce losses: we can treat the water to reduce the concentrations, or we can control drainage to reduce the flow.
There are several ways to treat field water. To treat nitrogen, the water can be run through a wood chip filter (called a bioreactor) that can reduce nitrate levels or it could be filtered through soil and a vegetated buffer (called a saturated buffer). For phosphorus, water can be filtered through iron, calcium or aluminum media that can filter the water. The BPBA has done research on a few other media to trial phosphorus removal structures on the Peninsula, which was presented at D-Day after lunch.
The other way to reduce nutrient loads is to minimize the flow by controlling drainage. Control structures are basically underground dams within drainage systems that can hold back water and raise the water table the height of the stop logs. In this way, water outflow from a system is reduced by 20-40 per cent and both N and P losses by the same, according to Purdue University’s research. Obviously, bringing up a field’s water table needs to be done carefully, especially when there is a growing crop in the field or when there are heavy rains in the forecast. Technology now allows for automatic control gates to be programmed based on soil moisture probes or via software.
While the term “controlled drainage” is often left to the scale of a field’s tile drain system, its definition can be so much more encompassing. Tile outlet ponds are a farm-scale solution for controlled drainage. This pond water can be irrigated back on the field through overhead systems or, if the grade is flat enough, through the drainage system itself. If the control gates are in place at every 1 foot of fall and the slopes are ~ 0.1 per cent within the drainage system, water can be pumped to the top during dry periods and flow right back into the system it came from, to infiltrate back into the soil. The flat grades of much of the northern Peninsula make it an ideal location for controlled drainage, though subirrigation would require a restrictive layer below the level of the tile to be able to raise the water table.
After lunch that was served up by Bear Tracks Inn and Restaurant, John Rodgers, outlined the Bruce Peninsula Biosphere Association’s work on phosphorus treatment. Rodgers is a farmer, retired teacher and BPBA’s research coordinator, who has partnered with Dr. Bulent Mutus from the University of Windsor and done years of research into phosphorus removal media on his farm near Lion’s Head.
They have researched tomato plant roots in the past and are now having success with an iron chloride dried on cedar bark. They have tested both high and low concentrations of phosphorus in water, through both passively-drained filters and actively pumped filters. The project involved developing the P sorbent media (carboxymethylcellulose – iron) at a larger scale and testing it in the field. As well, they have designed and tested a controlled drainage structure that could be automatically triggered by remote sensors in other parts of the watershed through Internet of things (IoT) technology.
This research was funded by Agriculture and Agri-food Canada’s Agri-Science program and also by the Canadian Agricultural Partnership through the Ontario Agri-food Research Initiative administered by Bioenterprise.
Rodgers went on to discuss some of the drainage concerns he was having on his own farm and the potential that road bridges were now under-sized and creating flooding issues upstream. D-Day concluded with a presentation by Jenny Chen of Wonderfull Inc, a distributor of DJI agricultural drones. Their drones can now do spraying and cover crop seeding as well as making high-resolution elevation maps that will be important for drainage system design.
Farming on the Peninsula has never been easy. Jutting out between Lake Huron and Georgian Bay, farmers have extreme rains and longer periods of drought than their neighbours to the south. As well, with more cottagers and tourists by the year, they are under more scrutiny than most. Controlled drainage and phosphorus treatment structures will be important to consider as drainage infrastructure is upgraded on the Peninsula. ◊