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Growing your own N

New research in Saskatchewan proves forage rotations of only two years can provide a valuable fertility boost

When Duane Thompson talks about sustainability, he makes no bones about the fact that nothing is sustainable unless it’s economical for the farmer.

“Sustainability is a nice notion but you want to be improving and getting better,” he says. “I’m not really big on sustainability — I want to be sustainable-plus.”

Thompson is a case study for how a focus on sustainable management practices can actually be profitable in the long run. He runs a mixed crop-livestock operation on 8,000 acres near Kelliher in Saskatchewan’s Aspen Parkland. For the last 15 years, he’s made it his mission to increase soil organic matter on every one of those acres by including forage legumes in the rotation.

His formula: he runs five to seven years of clover or alfalfa, followed by oats, canola, wheat, barley or oats, and peas. If the field is not being seeded to forages after that, it gets canola again followed by wheat. Some fields run on 14-year rotations.

The result is a significantly decreased need for fertilizer inputs (he’s grown over 60 bushels of canola per acre on 30 pounds of N), and improved water infiltration and soil organic matter (the latter, in some fields, by a factor of three).

“The system is more than economical. We have fourfold increased our land base and increased our cattle by a factor of 10 at least,” he says. “My kids are coming back to the business and it’s exciting to say we can support more houses on the land base.”

A five- to seven-year stint of forage legumes in the rotation is not possible for every producer. But new research in Saskatchewan proves forage rotations of only two years can decrease N fertilizer costs.

Nitrogen benefits

An Agriculture Development Fund (ADF) study, “Short rotation forage legumes for reducing fertilizer costs in Saskatchewan,” aimed to quantify N fertility remaining in the soil after two years of forage legumes that could be available to subsequent annual grain crops (in shorthand: NFRV, or N fertilizer replacement value).

The study, a collaborative effort between the Western Beef Development Centre (WBDC), Swift Current’s Wheatland Conservation Centre and Agriculture and Agri-Food Canada, ran from 2010 to 2013 on sites with a wide range of soil types — Swift Current (brown soil zone), Saskatoon (dark brown), Lanigan (thin black), and Melfort (black).

Rotations included alfalfa-alfalfa-wheat-canola, red clover-red clover-wheat-canola, barley-pea-wheat-canola and barley-flax-wheat-canola (control).

“After two years, the average cumulative net return on the alfalfa rotation ($346 per hectare) exceeded the control rotation (B-F-W-C), and the red clover rotation ($236 per hectare) was competitive with the control rotation ($298 per hectare),” concluded the study.

The results did depend on location, says study lead Paul Jefferson, vice-president of operations at the Western Beef Development Centre. The highest NFRV came from Melfort, which had excellent moisture in the years of the study. The lowest came from Swift Current, where there were drought problems during the trial years.

“Producers can see the advantage of using more legumes, not just for pasture rejuvenation and hay yield but to improve their cropland and their neighbours’ cropland,” says Jefferson. “Also it can produce high-quality feeds. A lot of guys aren’t mixed farming anymore, but we thought, ‘if producers have an annual crop neighbour, can they make an agreement with them?’”

Jefferson says forage quality was excellent with the study’s alfalfa and red clover, and in a straw blend they could be valuable to cow-calf operations. In Saskatchewan, where rain during hay harvest can wreak havoc on quality, high-quality forages can be used as a feed mix with lower-quality hays.

“It’s not a complex system. Producers only have to look at utilizing a crop they know well, using these crops in a different way,” he says.

Phosphorus availability

University of Saskatchewan soil scientist Jeff Schoenau was also involved in the study, analyzing phosphorus cycling and availability for short-rotation forage legumes, as well as NFRV.

He agrees that for many annual crop producers, five to seven years may be too long to have forage legumes in the rotation, but a couple of years could still offer significant benefits for nutrient availability.

In the ADF study, forage legumes didn’t have a negative impact on P availability due to their deep-rootedness — their ability to draw P from deeper in the soil. “Despite the fact that forage legumes remove phosphorus from the soil, we didn’t see a depletion or drawdown of P pools in the soil, which indicated that those legumes helped maintain P fertility,” says Schoenau.

Over the long term, however, forage legumes are high users of P and some other nutrients, and if annual crop producers are haying they will eventually have to replenish what they remove. “But there’s an opportunity to benefit from the soil improvement qualities of legumes in rotation to bring in some fixed nitrogen, to recycle some nutrients from depth, and in cases where we have excess water, these legumes help lower the water table,” Schoenau says.

The upshot of the study: depending on soil zone, there can be significant nitrogen benefits from including forage legumes in the rotation, even in the short term.

For producers like Thompson, it’s a technique that could be called “sustainability-plus.”

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