Features Agronomy Fertility and Nutrients
Long-term zero-till pays back

Much has been written about the soil quality benefits of zero-till, including
increased organic matter, increased water infiltration and better soil tilth.
Now, proof positive that no-till pays in higher yields, better protein and reduced
nitrogen costs.

In 2002, researcher Guy Lafond with Agriculture and Agri-Food Canada in collaboration
with the Indian Head Agricultural Research Foundation (IHARF) had the opportunity
to investigate the differences between a 20 year old zero-till field and a field
that was in a long-term wheat-fallow rotation on area farmer Jim Halford's land.
Halford, a long time zero-till advocate, and developer of the Conserva Pak Seeding
System, had picked up the wheat-fallow field in 2001.

Plot comparison of check (left) and 84lb/ac N placed mid-row. Photos By Bruce Barker.

The results that year were surprising: the advantages of long-term zero-till
were clearly outlined. Since then, the evidence has been building up, supporting
what Lafond discovered. The research site, on a sandy clay loam soil, now has
more than 400 plots spread over 10 studies comparing everything from nutrient
response in cereals, oilseeds and pulse crops, to risk management in split applications
of nitrogen fertilizer.

"The check plots tell the story. We keep the check plots in the same place
so that we can see the cumulative effects of long-term no-till relative to the
short-term zero-till plots," explains Lafond. "The program is building,
but we have seen some pretty interesting results."

The most interesting comparison, in these years of high fertilizer prices,
is the relative yield response of crops to nitrogen fertilizer. Back in 2002,
Lafond found that the long-term zero-till plots were much more profitable at
lower nitrogen rates, reflecting the zero-till soil's ability to release higher
levels of mineralized nitrogen from organic matter.

In that first year of study, the conventional field was converted over to zero-till
cropping and treated the same as the long-term zero-till field. Essentially,
Lafond was not only hoping to see the short-term difference, but was also hoping
to find out how fast the wheat-fallow land improved under zero-till.

On the long-term zero-till land, the yield of wheat in 2002 was 42.6 bushels
per acre compared to 26.2 bushels for the short-term field, when no fertilizer
was applied. Roughly estimating economic returns in 2002 dollars, the net returns
when no fertilizer was applied to the long-term zero-till field were greater
than any other nitrogen treatment for the short-term field. That is a remarkable
demonstration of the amount of nitrogen released from organic matter. Not that
this would be a sustainable practice, but it illustrates the improvement in
soil quality under long-term zero-till.

In the 2002 results, optimum yield on the zero-till field was obtained at 53
pounds per acre compared to 80 pounds per acre on the short-term field. With
a savings of 27 pounds per acre, that translates into a savings of $13.50 per
acre with $0.50 per pound nitrogen.

When a partial economic analysis is completed, the long-term zero-till field
had the best net return at $83.51 per acre versus $42.82 per acre for the short-term
field.

The results from this project puts economic numbers to what researchers, Ken
Greer and Jeff Schoenau of the University of Saskatchewan, found on Halford's
land back in 1990. Back then, Halford had noted that he could grow a 45 bushel
per acre high protein wheat crop on approximately 40 pounds of applied nitrogen
per acre.

Greer and Schoenau compared Halford's zero-till field with a neighbour's wheat-fallow
field. Surprisingly, they found that the total level of nutrients available
was not substantially different between the fields. Rather, what was different
was the level of nutrients that were mineralized into plant available form.
The researchers found that the zero-till field had twice as much nitrogen mineralized
as the wheat-fallow field in the top two inches.

The study report says that, "One must conclude that the quantity of organic
nutrients alone may not be the best indicator of soil productivity. Organic
matter quality, indicated by the ability to mineralize organically-held nutrients,
is more useful in ranking soil quality. The mineralized fraction of the total
organic N and S was least in the wheat-fallow rotation. Zero-tillage improved
the mineralizable fraction through fertilization and residue addition."

Then, in 1998, Agriculture and Agri-Food Canada Swift Current researcher, Brian
McConkey looked at the fields to determine the levels of total nitrogen in native
prairie, 20 year zero-till field and the conventionally tilled field. Total
pounds of nitrogen per acre in the zero-till field on the knoll-tops had over
1600 pounds per nitrogen more than the conventional soil, and the zero-till
field approached that of native prairie.

McConkey also estimated the potential mineralized nitrogen in the top three
inches of the soil. He found that an extra 50 pounds per acre on knolls, and
63 pounds per acre of mineralized nitrogen was potentially available, compared
to conventionally tilled fields.

"The increase in soil organic matter translates directly into higher rates
of nutrients being mineralized and made available to the crop," says Schoenau.
"It's not a sudden process that happens in the first year of zero-till
farming. In the first three to five years of zero-till, fertilizer requirements
may actually increase."

Back to the future

Lafond hopes to quantify – not only the long-term benefits of zero-till
but how fast farmers can get there when converting land from a conventional
tillage system.

Since 2002, the IHARF plots have suffered the same environmental problems as
farmers in southeast Saskatchewan, so the differences in the last few years
have not been as dramatic as 2002. In 2003, drier than normal conditions limited
yield potential at the site. Still, a nitrogen response trial with wheat and
oats on the short and long-term zero-till plots has indicated that the long-term
zero-till field reached maximum yield at about 27 pounds of nitrogen per acre
less than the short-term no-till.

In 2004, a late August frost compromised crop development and grain yields.
The agronomic and economic performance of the crops were poor. The frost was
actually harder on the long-term zero-till fields because of differences in
crop development at the time of the frost.

Lafond says that some of the long-term zero-till yields in the general area
were amazing – canola yields in the high 50s, for example, means the equivalent
of 180 pounds of nitrogen per acre just in the seed.

That's the benefit of having good soil fertility. In 2005 we had tremendous
mineralization of organic nitrogen. When the environment lines up, these types
of soils can carry through and deliver tremendous yields," says Lafond.

Lafond cautions that the amount of nitrogen released through mineralization
varies from year to year, depending on moisture and temperature. Because the
weather cannot be accurately predicted, appropriate fertilizer decisions must
be based on soil testing and an estimation of how much mineralized nitrogen
might be released from the soil. The benefit of long-term zero-till soils, though,
is that in years when good conditions encourage crop growth, the soils have
a large bank of organic nitrogen mineralized to help the plants take advantage
of the good growing conditions.

For his part, Halford says that long-term zero-till is paying off. His higher
levels of organic matter has meant about a 40 percent reduction in current fertilizer
rates, while harvesting a respectable 45 to 50 bushels per acre of hard red
spring wheat. "It's the difference in applying 50 to 60 pounds of nitrogen
versus a more traditional 90 pounds per acre. And when we're looking at nitrogen
in the 40 cents per pound range, that's a savings of $12 to $16 per acre,"
explains Halford.