“Sixty-five pounds of nitrogen per acre is very possible in Manitoba.”
– MARTIN ENTZ
Researchers tending the fields at the University of Manitoba’s research farm here have another duty to add to their daily roster – moving sheep.
A small flock of ewes and lambs has taken up residence on site as part of the organic crop management studies.
They’re there to help researchers confront one of the biggest dilemmas facing organic crop production – how to make the all-important green manure component of an organic rotation pay for itself.
Martin Entz, the agronomy professor overseeing the low-input cropping systems research, said the organic rotation of spring wheat, soybeans, green manure (usually peas/ oats or hairy vetch/barley), flax, fall rye and oats has been working reasonably well.
But one of the drawbacks is
the green manure component of the system. While it is necessary for replenishing nutrients and helping to control weeds, it requires an outlay of about $70 per acre with no opportunity to directly recoup that cost.
The farmer does get that back in the form of improved fertility in following years. For every 1,000 pounds of biomass, the farmer gets about 25 pounds of nitrogen, Entz said. “Sixty-five pounds of nitrogen per acre is very possible in Manitoba,” he told a tour July 23.
Entz said he recommends against organic farmers measuring their soil nitrates in the spring through soil tests, because it doesn’t provide an accurate picture of what is taking place in their soil. “Legumes are mineralizing nitrogen all year and you can’t pick that up in a soil test,” he said.
Entz recommends organic farmers send samples of their crop at the dough stage for a feed analysis, which show the nitrogen/protein content. Those tests also measure micronutrients.
But even if they are getting a shot of low-cost fertilizer out of a green manure crop, many farmers can’t fathom the thought of receiving no cash revenue from a portion of their land every few years.
So researchers began looking for ways to make green manure pay.
One option is to graze it. The sheep pens are moved so they can graze an area 10 square metres per day. Preliminary data suggests that a dense pea/ oat green manure crop can pro-
ROLLED AND CRIMPED: University of Manitoba agronomy researchers Gary Martens (l) and Martin Entz examine a barley/hairy vetch green manure crop that has been newly rolled and crimped at the university’s research station at Carman.
vide 800 grazing days per acre for sheep.
Livestock retain only about 10 to 20 per cent of the nutrients they consume, which means 80 per cent is returned to the soil in a form that is more readily available to following crops. Plus, the farmer has lambs to sell in the fall.
Entz said other ruminants and even pigs are also a green manure grazing option. “It makes the green manure phase into a revenue-generating crop,” he said.
Another option is to hay it. But trials comparing what happens to the following year’s flax crop in plots that were hayed compared to plots that were left shows the hayed fields had more weeds and the non-hayed plots have more nitrogen. They won’t know until after harvest how that affected yields.
Researchers are also making headway at reducing tillage, another weakness in organic cropping systems. A roller apparatus imported from
NEW RESIDENTS: A FLOCK OF SHEEP HAS TAKEN UP RESIDENCE AT THE UNIVERSITY OF MANITOBA’S CARMAN RESEARCH STATION AS PART OF A GRAZING GREEN MANURE TRIAL.
Pennsylvania is being used to roll and crimp the green manure crops in a way that makes it possible to direct seed into the residue the following spring.
The weighted roller simply flattens the green manure crop, in this case a mix of hairy vetch and barley, without cutting it. “A no-till seeder can deal with anchored residue much more easily,” Entz said. The crop is still grazeable.
“With this roller, I think we can eliminate half of the tillage in organic rotations,” he said.
Researchers are also studying wheat varieties to determine whether some lines perform better under organic management than others. And they are looking at various methods of non-herbicide and minimum-tillage weed control.
It’s not just organic farmers who might benefit.
“A lot of these techniques we’re using would also be useful in other low-input systems,” noted Entz. [email protected]