Agriculture and Agri-Food Canada research scientist Bruce Gossen says the 18-year study was boring, but its results weren’t.
Gossen and his colleagues took a long-term look at the effects of cropping diversity and inputs at Scott, Sask., from 1996 to 2013, but they didn’t just evaluate yields. They also looked at disease, insect and weed pressure, and evaluated what it meant for the bottom line.
“From a disease standpoint, I tell people it’s the single most boring study I’ve been involved with. If you start with no disease problems and don’t bring in any disease problems with low-quality seed, and use a diverse rotation, what you end up with is no disease problems,” Gossen says.
But he and his colleagues were far from bored by the study’s conclusions. According to their data, “penny-pinching‚” and using the bare minimum of inputs, when combined with the use of good seed and diverse rotations, resulted in good yields, good disease control, and ultimately, higher net returns.
The study compared three systems: 1) a high-input, tillage-based system, with levels of fertilizer and pest control products that conventional farmers might apply to optimize yield and quality; 2) a reduced-input, no-till system, modelled after management decisions “penny-pinching” farmers might make to optimize net return; and 3) an organic system.
Within each system, the researchers compared three rotations for a couple of years: a very simple cereal rotation, a diversified rotation including canola and pulses, and a highly diversified rotation including alfalfa.
Covering a huge land area — roughly 10 hectares — the research was based on a split-split approach for reliable results. In particular, the design meant the research team could separate treatment effects from weather effects.
“Because of the study’s internal design, we’re very confident that the patterns that came out of it actually reflect what is likely to occur across a broad area of the Prairies,” says Gossen.
Good cultivars, good seed
From Gossen’s perspective, the study’s most interesting results came from the high-input and reduced-input comparison.
On average over 18 years, there was very little difference in yield between the high-input and reduced-input plots. In fact, in the study’s third cycle (2008-13), the reduced-input plots saw higher yields overall.
In the reduced-input plots, the researchers aimed to be conservative on multiple levels.
“If we thought we could get away in a dry spring with a lower fertilizer rate we went with that. If there was a cheaper herbicide option that would give us almost as good control rather than 100 per cent control, we’d go for the lighter or cheaper option. If there was a way to save an operation or save a few pennies we did that,” Gossen explains.
There were a few key areas in which no expense was spared. The researchers always used good cultivars and good seed to avoid introducing problems along with the seed.
“What we found over the course of that study was that there was remarkably little difference, in a numerical or statistical way, between high inputs and reduced inputs,” Gossen says.
“What you’d expect is that there would be some advantage over time to getting really good weed control and putting on enough fertilizer so you could maximize yields. But that’s really not what we saw. For example, you lose a little yield potential in a wet year if you haven’t put on enough fertilizer. But in a dry year, if you over-fertilize, you don’t get a yield advantage. The numbers were very, very close over time.”
Weeds and disease
Steve Shirtliffe, a professor in the College of Agriculture and Bioresources at the University of Saskatchewan, was also involved in the study. He says there was also little difference between weed densities in the high- and reduced-input plots. Weed densities were highest in organic plots, but interestingly, weeds were not the primary cause of yield loss in organic plots — that honour went to nutrient depletion in the soil.
But Shirtliffe’s interpretation of the study’s significance differs from Gossen’s in that he sees tillage rather than inputs as the biggest difference between the systems: weeds were controlled with tillage in the high-input and organic systems, and with glyphosate in the reduced-input systems if thresholds were exceeded.
When it comes to inputs generally, Shirtliffe believes farmers have become habituated to using higher levels due to “upsell” marketing. For example, it’s difficult for some to refrain from using fungicides, even in dry years.
“When there’s disease there, fungicides work, but last year we had a drought. How many people chose to forgo their fungicide applications because of mythical yield-enhancing benefits even though there wasn’t disease there?” Shirtliffe asks.
Still, in his view, there is no ideal agricultural system.
“Growing crops is a strange thing — not a normal ecosystem. You’re growing a lot of something and taking it off and out of the system, so at some level you have to address problems with that system. One problem is that you’re taking nutrients off. Another is that you’re growing just one species,” Shirtliffe says.
Gossen believes not enough respect is paid to what he calls the “natural biological controls” that occur in the background of well-managed systems. “You don’t need to add to it or take anything away because it’s always there,” he says.
By oversimplifying rotations and using high levels of inputs, we’re putting more and more pressure on agricultural systems to select for insects, microbes and pathogens that are more effective than they’ve ever been.
“To accommodate bigger farms and fields and larger equipment, we’ve been taking out sloughs and windbreaks, breaking headlands and field edges, and we’ve gone to simpler cropping rotations,” he says.
It’s not just insect predators and parasites that live in these sloughs and windbreaks, but diverse micropopulations that help break down inoculum from year to year. In other words, we’re allowing disease pressure to build up to the extent that we’re over-relying on resistance genes and fungicides.
“That increased reliance has another side effect, which is that we have more instances in field crop production of breakdown of resistance to diseases and loss of efficacy of fungicides,” Gossen says.
When it comes to disease management, his advice to farmers is to start with no diseases, use good seed and good rotations.
“You’ll end up with no problems,” he says. “That applies broadly across crops and diseases. Even for some of the most problematic diseases, that is going to help, even if it’s not the only solution. Penny-pinching on everything but seed is probably a good strategy for maximizing returns year on year.”
Bruce Gossen’s guide to disease management
- Disease management activities should be almost complete before any crop is planted.
- Plan for a diverse crop rotation: three to four years, alternating cereals with dicots. Even different cultivars can be useful if they carry different sources of resistance.
- Use the best genetics for your region: high yield, suitable days to harvest, good disease resistance.
- Don’t plant problems with the crop. Use seed with high germination and vigour, treated and inoculated, minimal/no pathogens with seed.
- Provide isolation from last year’s heavily infected fields.
- Scout fields and apply a foliar fungicide only if required.