Standing on the edge of his overgrown field, John Hardman of Dauphin, Man., commented on the thick stand of growth that had accumulated since he was last able to get on it with a tractor. “My grandfather grew clover in this field 40 years ago,” he says. “I was lucky and ended up with a volunteer crop of it this year. It’s like a weed; you never really get rid of it.”
The overgrown field wasn’t the plan, of course. Due to extremely wet conditions, Hardman hand’t been able to seed or get on the field.
That clover growth really was a stroke of good luck. Hardman spoke to an agronomist to discuss his options, and he decided to use the volunteer clover and other weeds as a green manure crop to recycle the nutrients they contained. “She said I could get up to 90 pounds of N (per acre),” he says. “I’m doing the make lemonade out of lemons thing.”
But getting the tangle of plants incorporated back into the soil was far easier said than done. “It was up to the hood on my 1070 Case tractor when I mowed it,” he says.
After cutting the field with a rotary mower to make it easier to deal with the growth, Hardman decided to use his IH model 700 plow to bury all the plant material. Although the plow has been in his machinery fleet for some time, it doesn’t see regular use. This year, however, he decided it was the right tool for the job. “I thought, I had it, so why not use it?”
DISCS VERSUS PLOWS
“Normally I don’t plow every year,” he says. “It takes a little longer than my cultivator would, but it only (takes) one pass. My discs aren’t heavy enough (for these field conditions).”
Using a plow instead of a heavy disc may offer some advantages, according to Patrick Mooleki, a soil and nutrient management specialist at the Saskatchewan Depar tment of Agr icul ture, although he notes each implement has its own benefits. “The disc will incorporate the material better,” he says. “But the disc also pulverizes the soil.” That increases the risk of wind erosion. The plow leaves a more stable surface that’s better resistant to blowing.
“The disc chops and mixes the material with the soil; the plow simply turns the soil over, burying the material,” Mooleki says. “Chopping it creates more surface area, which increases the rate at which it breaks down. The faster it breaks down, the better it is for the green manuring process.”
SPEEDING UP THE BREAKDOWN PROCESS
Typically, plant organic matter takes several years to fully recycle the nutrients it contains. Farmers should see the biggest benefit in the following year after terminating a stand, when about 10 to 20 per cent of those nutrients become plant available.
“The first year benefits more from green manuring than the second,” says Mooleki . “Probably, for the next 10 to 15 years that nitrogen will still be made available, slowly.” The reason is nutrients within a plant are in organic form. In order to be recycled, they must be mineralized, only then are they available to subsequent crops.
By cutting the field with a rotary mower before plowing, Hardman’s green manuring procedure gets the benefit of faster material breakdown without leaving the soil pulverized from discs. And because he uses a traditional approach to plowing, having the plants cut down makes it easier for him to measure out the distance necessary to create precise furrow spacings.
By limiting the depth his plow goes down, he doesn’t have a problem with mixing soil horizons. The necessity to work deeply seems to be one of the popular misconceptions about plow use. “I’m not going much deeper than I would with my deep tillage cultivator,” he says.
SMOOTHING OUT THE ROUGH SURFACE
Bill Agnew of Hartney, Man., is another farmer who has chosen to reclaim overgrown fields with a plow. Sitting at the wheel of his 9280 Case IH tractor pulling a model 900 IH plow, he looks back at the tall, standing mass of weeds disappearing behind each moldboard. “It does a pretty good job,” he says. Ahead of Agnew’s tractor is a stand of various weeds and volunteer crop waist high and taller.
Agnew plows with a different style than Hardman, which allows him to simply turn weeds directly under. That pays dividends in time saved, which is important to him because he has an off-farm job. “I’ll go over it (the field) with the cultivator in a couple of weeks once all the plants are dead,” he says. That will help further incorporate everything and smoothen out the relatively uneven surface left by the plow.
Agnew is a certified organic grain grower and has used plows for several years. “I started with a seven-bottom, then had an eight, now I have this one,” he says of his current 12-bottom model. Although he’s no stranger to using it, putting it to work in fields as overgrown as his are this year due to the wet weather is a new experience. He wasn’t able to seed any acres at all this spring.
Most of his neighbours, who are conventional growers, are facing the same problem with overgrown fields; some were interested in seeing the plowing
results. “I’m sure a few guys will be around to see how it turned out,” he says.
Although it would be a pretty rare sight to drive down a road on the Prairies and see anyone using a plow, the farmers who do use them may not be in a club as exclusive as most may think, sayss Hardman. He had recently gone to his local Case IH dealer to buy replacement shares for his and was surprised by the response. “I thought I’d have trouble getting them,” he says. “But he (the parts person) said they could get them out of Regina overnight. He told me they sell about 80 to 100 a year. I don’t know who else buys them around here.”
THE CARBON TO NITROGEN RATIO
For farmers with overgrown fields, using tillage to bring them back into condition may be one of the few options available, and it has the potential to be a good one. Mooleki says using a green manuring practise creates a soil benefit that goes beyond just recycling the nutrients contained in growing plants. “It improves the quality of the soil, because you’re also adding carbon. You have the added advantage of increasing organic material in the soil,” he says.
Just mowing the growth and leaving it on the surface would protect the soil, but nutrient recycling would take significantly longer. With many no-till growers already struggling to cope with high residue levels, this approach isn’t viable for many.
Farmers worried about tying
up available N in the soil after incorporating so much plant material shouldn’t be, says Mooleki. Green, growing plants have a much lower carbon to nitrogen (C: N) ratio than dead, dried plants, such as cereal straw. The problem doesn’t occur to any extent to worry about.
Getting the C: N ratio right is important, however. “(With the right balance) you probably won’t see a significant blip in the rate of mobilization,” says Mooleki. Applying synthetic fertilizer the following crop year won’t be adversely affected.
To get the proper C: N ratio, Mooleki says farmers should terminate green manure stands while they are still actively growing. “(At that stage) the crop has not started mobilizing most of the nitrogen into the seeds,” he says. “The stems are still nice and succulent. [They] will break down faster. The other thing is the crop has not sucked too much moisture from the system (soil).”
ScottGarveyismachineryeditorfor Grainews.Contacthimatscott. [email protected]
The necessity to work deeply seems to be one of the popular misconceptions about plow use