Cure-all or problem for phosphorus loss?
Most farmers know that conservation tillage has a variety of benefits – economic, agronomic and environmental – but conservation tillage can potentially have some less than positive side effects as well. Don Flaten, a Crop Nutrition and Nutrient Management specialist from the University of Manitoba presented recent research on conservation tillage from Manitoba at the Innovative Farmer’s Conference in London this month.
Flaten’s research shows that even though conservation tillage reduces nitrogen loss from surface water and sediment loss, in some situations, particularly in Manitoba where a number of trials were performed, it also increases phosphorus loss. It is this example that led Flaten to conclude that we need be more objective when implementing best management practices.
In the early 1990s, says Flaten, a group of farmers wanted to evaluate and demonstrate the value of conservation tillage and its effect on water quality. The results were surprising.
“I think everyone associated with the project was expecting the water quality to be better on the conservation tillage field than it was on the conventionally tilled field,” says Flaten. It came as a real surprise when research showed that a high proportion of the nutrients that were lost were lost in the dissolved form.
“That was unusual,” says Flaten. “But because our prairie soils are often frozen at the time of runoff – because 80% of our runoff is typically snowmelt – that makes more sense now in hindsight. But it came up as a surprise when the initial results started to come in.”
If your biggest problem is erosion and the loss of this particulate form of phosphorus, conservation tillage could still be very beneficial in terms of reducing phosphorus loss. “However, in a situation like ours here in Manitoba where our main form of phosphorus loss is in the dissolved form, then conversation tillage has a tendency to just make that problem worse.”
“The fact that there was a mixture of benefits and negative side effects – that we saw reductions in nitrogen loss, reductions in sediment loss, but an increase in phosphorus loss – that gave us some real challenges,” he says. He concluded, therefore, that as beneficial as it was in some way, conservation tillage was more of a problem than a solution for many Manitoba farmers.
It’s research like this that reveals the importance of looking at all management practices objectively, rather than viewing them individually a possible cure-all. In everything they do, farmers must acknowledge that there will be both positive and negative side effects. Management practices will be heavily dependent on the situation – and the location.
The second part of Flaten’s message came in the form of a powerful suggestion. He thinks that maybe it’s time to look at some of our best management practices in new and different ways, where we are careful to examine them objectively for all of their benefits and costs – economic, agronomic and environmental.
“Even more universal,” says Flaten, “is the importance of keeping our eyes open for the pros and the cons, the benefits and the side effects of our beneficial management practices. Because it isn’t just conservation tillage that has these potential side effects – it’s almost everything we do in agriculture.”
The farmers in attendance at the Innovative Farmer’s Conference were receptive to Flaten’s presentation. “So far the feedback seems to have been positive,” he says. “I think farmers appreciate that the practices that they employ are complex and have a variety of benefits and costs. They’re probably, in many ways, more receptive to this message than some other people who may be more specialized.”
For example, he says, a scientist who just focuses on phosphorus may be very critical of conservation tillage because it has potential to increase phosphorus losses in the environment. “But if I’m a broad-minded person and I see that conservation tillage helps in so many other ways,” he continues, “I might accept the side effects as being all right when you consider all the benefits overall.
So while the results of the Manitoba trials were surprising to some, they did make sense in hindsight. He just didn’t anticipate them. “It’s a good idea to have some data, right?” says Flaten. “Invest in a little bit of research before you start promoting the heck out of a BMP assuming it’s going to solve all your problems.” •