No fast fixes to soil concerns: two views from two leaders
April 24, 2007:
Repairing damage to soil takes time — the question is how much time
Over the past 20 years soil conservation has become an important consideration for producers making decisions about their farming practices. It's also an era that has opened up a Pandora's Box of questions on just how long it takes to rebuild damaged soil.
Jim Halford and Elena Bennett arrive at the subject of soil conservation from two quite different perspectives. Halford's perspective is driven by 30 years as a soil conservation pioneer and an early champion of zero-till farming practices. Meanwhile, Bennett's views are the product of several years at the forefront of researching inland water.
What they have in common is respect; respect for the importance of soil and the importance of both conserving it and building back the nutrients in badly damaged soil. They also both acknowledge the important role of low-disturbance soil management practices such as zero-till in those efforts.
"Remediating soil phosphorous levels can be a slow process," says Bennett, a professor with McGill University in Montreal and an authority on the study of inland water. "It's the slowest factor in the ecosystem to recover and it can take hundreds of years to build it back from the effects of wind and water erosion, loss of organic matter, contamination and salinization.
"On top of that, runoff from overfertilized soil presents a water contamination threat. This requires us to be very cautious when making management decisions."
At the same time, Halford believes that practices such as zero-till have changed the rules of building back nitrogen levels in soil and can, in fact, help build soil back to reach or even exceed peak nitrogen levels over a relatively short period of time.
"There was soil on our land that had lost about a third of its original organic material over the course of about 100 years," he says. "According to a study by Agriculture and Agri-Food Canada, after I had been using zero-tillage for about 20 years, it was back to a little over 90 percent of its original content of organic material. Building back soil is a process that takes time, but not as much time as was generally thought in the past."
The zero-till revolution
Halford's views on soil reclamation are the product of almost 30 years on the front lines of zero-till farming practices as both an agricultural producer and a manufacturer of zero-till technology. Zero-till, he says, has driven a sea-change in how long it takes to build back damaged soil.
"When I was going to university, it was commonly thought that it takes hundreds of years to reclaim soil nitrogen," he says. "But I have evidence on my own farm and those of customers which shows that, when properly managed, it can be built back in a fraction of that time — possibly within a couple of decades."
The logic behind zero-tillage, from a soil conservation perspective, is that it helps the soil better retain nutrients developed from previous growth. Halford says nitrogen, whether it already exists in the soil or is enhanced by fertilizer application, is particularly important to this process because it can act as a catalyst for the growth of organic material.
On Halford's Indian Head, Saskatchewan farm, research conducted by Dr. Guy Lafond of Agriculture and Agri-Food Canada revealed that his soil required 30 lbs/ac less nitrogen to achieve the same yield as adjacent soil that had been conventionally-tilled using a fallow-cropping system. The study took place after Halford has been using zero-till on his farm for about 20 years.
Producers do not have to eliminate tillage completely in order to see an improvement in soil health, however. "Soil quality can improve somewhat by even just reducing the amount of tillage done on the farm," says Halford.
A slow changing variable
Bennett's primary discipline is limnology, or the study of inland water, lakes and streams. Looking at soil from a water quality and conservation context has given her a long-term perspective on the effects of soil erosion and the opinion that soil badly damaged from overfertilization can take many decades to reclaim.
"Because soil phosphorus is such a slow changing variable, a soil sample taken today is not just a reflection of what happened to the soil this year, but a piece of history that shows the land use and management practices of a hundred years ago," she says.
At the same time, it's important to manage soil nutrients from fertilizer responsibly in order to prevent damage to other resources. "When nutrient runoff gets into lakes, rivers and other watercourses, it causes accelerated algae growth," she says.
"This creates several problems. For one, too much algae content looks bad from an aesthetic perspective and tends to give off an unpleasant odour. Algae also robs the water of oxygen, presenting a threat to fish populations. From a human health perspective, we're seeing the presence of non-native, toxin-producing species of algae developing in water bodies that can make affected water bodies dangerous to swim in."
One watershed around a lake she studied accumulated around 500,000 kg of phosphorous every year, with 30,000 kg, or two percent, making it into the lake as runoff. That relatively small amount, however, was enough to stimulate a rampant growth of algae and compromise the oxygen content of the lake. "Essentially we would call that a non-leaking system and it still almost destroyed the lake," she says. Soil conservation practices such as zero-till, however, can play an important role in both soil reclamation and limiting nutrient runoff, says Bennett. Although zero-till practices generally require a high degree of fertilization, she says these practices, depending on the layout of the land and general management factors, often help minimize runoff into water bodies.
"We're finding that's the case with phosphorous runoff, although the jury's still out on zero-till's impact on runoff from nitrogen," she says. "Ultimately, the question we need to ask ourselves is how we can feed people without ruining the soil while considering water quality at the same time. It's a tricky balance."