Phosphorus levels in our lakes: Is no-till the culprit?

Monday, December 3, 2012

While no-till has reduced the flow of particulate phosphorus into the lakes, it may be adding dissolved phosphorus. As a result, says an Agriculture and Agri-Food Canada soil specialist, no-till shouldn't be considered a best management practice any more. Others are not so sure Phosphorus levels in our lakes: Is no-till the culprit?

Stephen Rigby fielded a lot of jibes from friends when he began farming with his father in 1985. That was the year his father, Jack, sold most of his conventional tillage equipment and they embraced no-till in earnest on the family farm near Rondeau Bay in Chatham-Kent. "'We were farming 'ugly' is one comment I do remember hearing," Stephen recalls.

The Rigbys were among the first in Ontario to adopt no-till and the first to use the technique to grow seed corn. A 1981 spring downpour that transformed their topsoil into a torrent of mud is what convinced Jack Rigby to look beyond conventional tillage. "We're on a mini-watershed that drains into Lake Erie – the Rondeau Bay basin they call it. There's a ridge that runs roughly between Blenheim and Ridgetown and the land slopes towards this bay," the senior Rigby explains. From the ridge to the water is a distance of about five kilometres and, within that stretch, the elevation drops 150 feet. That means water flows rapidly over land. But halting erosion wasn't the only problem on Jack Rigby's mind.

During the 1960s and early 1970s, public outrage erupted over pollution levels in Lake Erie. Nitrate and phosphate from untreated sewage spewed by the 17 urban centres and industries around the lake, and from agricultural runoff, were considered the culprits, as were industrial chemicals. Lake Erie, as the late comedian Johnny Carson once famously quipped, had become the place where fish went to die.

By 1972, Canada and the United States had signed the first Great Lakes Water Quality Agreement. Programs to rehabilitate the lake and control nutrient levels were underway.

Excessive nutrient levels promote massive algae blooms that can deplete oxygen in the water, which in turn kills fish. Blue-green algae blooms are actually bacteria that can be toxic to aquatic life, people and animals, if touched or ingested. But reducing the amount of just one nutrient type going into lake water and you'll limit overall algae and bacteria growth. Phosphorus is targeted because it is the smallest component that the plants need and therefore easiest to control.

Rigby figured the switch to no-till would not only keep his soil in place but also his crops' nutrients. (In no-till, the ground is only opened to plant. Crop residue is used to create channels in the soil for water and to prevent soil erosion.)    

By 2011, the farming technique Rigby championed and its derivatives – conservation tillage such as vertical, strip and reduced tillage – were being used on 81 per cent of the land area prepared for seeding in Canada. Soil conservation and health continue to be incentives but an even greater appeal is something the Rondeau Bay farmer discovered long ago: "We could farm cheaper, too."

Lake Erie had already begun its recovery before Rigby started no-tilling. By 1981, the lake's phosphorus load had been reduced to 11,000 tonnes from its highs, a decade earlier, of more than 25,000 tonnes.

In 1994 mayflies, which are to lakes what canaries are to mines, returned to Erie's western basin. Then, in 1995, the algae blooms returned.

Monitoring phosphorus levels
David Baker stands on the concrete aqueduct of the Lost Creek monitoring station and discusses water sampling. Behind the thin, bespectacled researcher a pump in the station gurgles like a draining bathtub. It's the only man-made sound in the dense Ohio bush on this June 2012 morning.

The creek is the Maumee River's smallest tributary. It's automatically sampled three times a day at this station. Heidelberg University's National Center for Water Quality Research, which Baker founded, operates 13 other stations just like this one. Most are in the Lake Erie basin. What's in the water is sampled, including both dissolved and particulate phosphorus – the form of phosphorus that algae and bacteria need to grow. Water volume is monitored, too.   

Many of the monitoring stations are in agricultural areas. Sixty-six per cent of the watershed's 4.9 million acres are in crops – mostly field crops – while only 13 per cent of the area is urban.

Baker has been conducting this sort of monitoring in the Maumee's watershed since 1975. What he's found is that while the amount of particulate phosphorus (phosphorus bound to sediment) has declined, the amount of dissolved (water soluble) reactive phosphorus has, on average, risen significantly since the mid-1990s.

The reasons behind the decline of particulate phosphorus are evident: tighter government controls on the release of nutrients from the watershed's 17,000 nutrient point sources (direct sources, such as water treatment facilities), conservation efforts like buffers along watercourses, and the adoption of conservation farming practices like no-till and reduced tillage.

But Baker and several other U.S. researchers think they may have found the answer to the source of the dissolved phosphorus, too: the interaction between climate change, tile drainage, fertilizer broadcasts and the same conservation farming practice credited with reducing particulate phosphorus – no-till.    

Moreover, he asserts that dissolved phosphorus levels in the lake began rising during the same period that farmers in the Maumee and Sandusky watersheds (another primarily agricultural watershed that empties into Erie's shallow western basin) began to switch to conservation tillage and no-till.

While the Maumee's flow only accounts for three per cent of the annual tributary flow to the western basin, he explains that research indicates it represents 75 per cent of the annual tributary solids load to the basin and 55 per cent of the annual phosphorus load – a far greater amount than the faster flowing, high-volume Detroit River. In 2009 and 2011, years when massive blue-green algae blooms appeared in Erie's western basin, dissolved phosphorus in the Maumee watershed spiked after spring planting during unusually heavy rains.  

Tiequan Zhang, an Agriculture and Agri-Food Canada research scientist who specializes in soil fertility, chemistry and water quality at the Harrow federal research facility in Essex County, finds Baker's conclusions unsurprising. His research also suggests that dissolved phosphorus loss is greater in no-till systems than conventional tillage.

Crops typically use only 15 to 20 per cent of the phosphorus that's applied in a year, he explains. Because soil is untouched in no-till systems, phosphorus becomes concentrated in the soil's surface layer, reducing its ability to absorb more and creating the potential for surface runoff.

The system also creates channels that offer excess phosphorus quick entry into drainage tiles. In the clay soils common to Essex County, "even in the summer or late fall you can see big cracks, sometimes down to one meter in depth," Zhang says. Long-term studies indicate that the majority of phosphorus loss occurs through tile drainage.

Zhang says about 75 per cent of agricultural soils in Ontario are either high or excessively high in phosphorus. Good management practices can limit phosphorus loss on soils with high natural levels and there are situations in which no-till will reduce erosion. But using no-tilling on Essex's heavy clays creates risk of phosphorus loss and provides little benefit for the farmer other than saving some input costs, he says. No-till "shouldn't be considered a BMP (best management practice) anymore."

Surprising connection
Kevin Eisses couldn't believe his ears when he first heard about the connection between no-till and dissolved phosphorus loss three years ago. After being in no-till for a while, "you just see the benefits," he says. Healthier soils. Healthier crops. Increased yield – "and often with less inputs just by managing those natural systems." To suggest that an approach that harnesses natural systems would be a detriment to the environment, "just doesn't seem quite right."

Eisses farms with his father, uncle and his uncle's family in Innisfil, south of Barrie, near Kempenfelt Bay on Lake Simcoe. He and his father have a dairy farm; his uncle raises poultry. Together, the extended family farms 2,500 acres of corn, soybeans, wheat and forages. They introduced no-till in the late 1980s by seeding their wheat into alfalfa slated for rotation in the fall. "We had pretty good success with that," Eisses says. So they expanded the practice to other crops in the early 1990s.

Eisses is keenly aware of phosphorus issues. In 2010, the province introduced a phosphorus protection strategy for Lake Simcoe. All of the watershed's stakeholders have been under pressure to determine how their actions might be contributing to the load, he says.

But after learning about the proposed connection between no-till and dissolved phosphorus, Eisses grew really concerned. He didn't want to see agriculture singled out. Farmers had already been blamed for contributing to water quality problems in the past – some, he says, quite rightly. Yet no-till had proved it could reduce the loss of particulate phosphorus in agriculture. He was wary of the science behind the new theory. "With the population involved in farming being small and getting smaller, it just becomes more important to proactively defend what we do as good practices for society, too," he says.

Eisses, along with a handful of other farmers across the province, recognized that there was a key question that the research supporting the connection hadn't answered. Was no-till creating the same effect in Ontario soils?

They formed a group called Answers, and for its nine members the objective is to ensure the science behind the claims of a connection between no-till and water quality is sound. To that end, they volunteer their farms for research to "improve what's going on with the environment, with nutrients and with our crops," Eisses says. All the members are involved in the Innovative Farmers Association of Ontario, which spearheaded the search for project funding.

Merrin Macrae, an associate professor in University of Waterloo's department of geography and environmental management, is one of several researchers working with the group on a study initiated in 2010 that compares conventional tillage, no-till and modified no-till by dividing each test field into different sections. They are studying two locations in the Lake Simcoe watershed and one in the St. Marys area throughout the seasons.

"We are making sure we are looking at how much phosphorus is actually leaving the fields and we're looking at that both in dissolved forms and in particulate forms," she says. Data has been collected since the beginning of 2011 and the goal is to run the study for at least 10 years.

It's too early to draw conclusions. But the weather swings of 2011 provided a good range of circumstances to test the performance of the different tillage practices. What the researchers are seeing so far is roughly the same rate of loss – small although higher during heavy rains – across all forms of tillage. "We need a longer data set to say this with confidence, but we've seen enough to question whether or not no-till is in fact resulting in much larger loading to drainage tiles than conventional till types," Macrae says.

She's not sure why their research shows different results from other studies. "We may have different soils; it might also be related to our agronomy," she says, noting that many farmers who define their practice as no-till actually incorporate a small amount of tillage.

"It really underlines the need to look across Ontario so that we capture a lot of different situations," she says.

Nutrient stewardship initiative
Site-specific differences may also be at play and, to determine just how much of a factor they might be, Macrae is involved in field-scale studies of phosphorus losses related to tile drainage and flows over land in different tillage types. Monitoring is taking place on Answers member farms throughout the province.

In Ohio, the state has responded to the proposed connection between no-till and dissolved phosphorus loss by introducing a 4R nutrient stewardship initiative. It's described in a March report as encouraging farmers to use "the right fertilizer source, at the right rate, at the right time, with the right placement."

The report, produced by Ohio's agricultural nutrients and water quality working group, recommends frequent soil sampling, avoiding spreading fertilizer on frozen or snow-covered ground, incorporating it as much as possible and maintaining detailed fertilization records. Government money is available to help farmers adopt practices to mitigate dissolved phosphorus loss, including cover crops, variable rate fertilizer application technology and controlled traffic farming (which employs GPS technology to ensure all farm equipment travels on the exact same lines in farm fields).

The report also recommends establishing mandatory standardized soil testing and a voluntary certified nutrient stewardship program, as well as licensing commercial and private fertilizer applicators.

Back in Ontario, outreach staff with the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) continue to encourage conservation tillage and no-till to counter what they've seen as an increase in tillage in recent years, says Adam Hayes, provincial field crops soil management specialist.  

You've got to think about the total system in terms of the environment, explains Gabrielle Ferguson, the province's environmental programs specialist. Conservation tillage, including no-till reduces the loss of particulate phosphorus and fosters soil health. There may be other measures, perhaps even something on an entire watershed scale, that can mitigate the loss of soluble reactive phosphorus from these systems if studies such as those Macrae and her colleagues are pursuing show there is such a loss. "To me, that's where the debate starts," she says. "Is the percentage increase in soluble reactive phosphorus more significant than the reduction in the total amount of reduced phosphorus due to reduced erosion?"

Lake Erie a priority
Meanwhile, scientists tackling Lake Erie's woes offer new perspectives on the role agricultural runoff plays. Sue Watson is a research scientist with Environment Canada's National Water Research Institute in Burlington and a member of an International Joint Commission committee that has been compiling research on the lake to develop recommendations on what to do next. The lake has been identified as a priority in the new, amended Great Lakes Water Quality Agreement signed by the Canadian and U.S. governments in September and Environment Canada has earmarked $16 million over four years to find solutions to its problems.

Watson says scientists agree that phosphorus and nitrogen are driving Erie's harmful blue-green algae blooms. But when it comes to the question of whether high phosphorus loads in the Maumee and Sandusky rivers are to blame, there has been a lot of finger pointing. "We need to stop some speculating and actually get some hard data to really back up our arguments," she says.

There are many complex processes at work in the lake. She uses the example of smaller algae blooms along the lake's northwestern shoreline.

Some researchers have blamed the blooms on the Maumee and Sandusky rivers. New research, however, shows that the Detroit River flows into the lake through at least two channels: a rapid flow containing mostly clean water from Lake Huron into the centre of Erie's western basin and another, more nutrient-rich and slower moving flow that may hug the northern shoreline.

Added to the mix is surface runoff along the northern shore that may be connected to Essex County's concentrated greenhouse industry and other development, as well as fluctuating lake levels and wind-driven water movement.

Normally, what's along these shores gets moved off shore quickly. But Watson says zebra and quagga mussels have colonized the area and their activity may be keeping the material in shore and completing the chain of events for local blooms to occur.

Moreover, Lake Erie's recovery may not have been as quick as previously assumed. She points out that even if all external sources of phosphorus are stopped, particle phosphorus on the lake bottom may be changed to a more available form through natural processes.

Researchers also wonder if they may have underestimated the impact of storm sewer discharges and sewage bypasses. A new study on the Bay of Quinte in Lake Ontario (one of the Great Lakes Water Quality Agreement's 39 areas of concern) indicates storm water and sewage bypass discharges may be a more significant source of phosphorus than previously thought. The study concludes that the annual amount of phosphorus from storm sewer discharges equalled that from the area's four sewage treatment plants, Watson says.

Those findings could reshape understanding of the contributions of Detroit's wastewater treatment plant. The plant, the world's largest such facility, has had a long history of sewage bypass violations.

Lake Erie in recovery is far different from the one in decline 50 years ago. Shoreline development has changed its shape. Dredging, diversions and declining water levels alter the circulation of nutrients and algae. New species arrive. Climate change affects the circulation activities that release internal phosphorus reserves and fosters more algae activity by warming the water.

"We cannot expect it to behave exactly the same way to the same amount of phosphorus inputs as it did going the other way," Watson says. Today's lake reacts far more rapidly to the addition of nutrients.

For all of the activities along its shores, including agriculture, the status quo therefore is not an option.

Yet we need to remain pragmatic. Yes, fertilizer makes an impact on the environment. But we do need to eat, Watson wryly observes. "We need to support the farmers and whatever has to be done should be done with good guidance and not leave them out to hang and dry." BF