An organic crops field lab at the University of Manitoba’s Carman research station is providing a long-term site for plot-scale organic field crops research.
John Hollinger, an organic business development specialist with Manitoba Agriculture, said the practices used in the field lab are applicable to any conventional or organic grain farm that doesn’t have livestock as a nutrient source.
Martin Entz, who established the field lab, designed a six-year rotation that accounts for limiting factors inherent to Carman-area farms: erosion susceptible soils; poor drainage, and a history of broadleaf weeds and leaf diseases.
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Year 1: Berseem clover
The annual legume, also known as Egyptian clover, tolerates both drier-than-normal and wetter-than-normal conditions. After being cut for hay, once or twice depending on moisture received, the berseem clover re-growth is plowed down in autumn. The seed costs about $20 per acre and the clover contributes about 100 pounds of nitrogen per acre to the soil.
Year 2: Flax
Flax thrives in rotations following clover because of lower weed populations, and flax does not compete well with weeds. Flax also sells readily in the organic marketplace, and few insects or diseases bother it.
About 60 lb. of nitrogen per acre will be removed from the soil by the flax, which looks like it will yield about 20 to 25 bushels per acre this year.
Year 3: Oats
Alternating broadleaf and grassy plants on a continuously cropped field is always a good idea, so oats make good sense in Year 3.
Oats are also easy to market, which makes them a good choice to follow flax in the rotation. This year’s crop of about 70 bu. per acre will remove nearly 80 lb. of nitrogen per acre.
The variety AC Assiniboia grown in 2006 has shown that a rust-resistant variety would have been a better choice, given the history of rust on this farm. The incidence of leaf rust in the oats this year most likely restricted both yield and bushel weight.
Year 4: Chickling vetch (green manure)
The nitrogen budget is now minus 40 lb. nitrogen per acre, so a leguminous green manure is used in Year 4 to put some back in, about 100 lb. per acre in the case of chickling vetch.
Also known as grasspea, chickling vetch breaks down easily in the soil and much of the nitrogen is readily available to the succeeding crop.
The seed costs about $20 per acre. Vetch, like most green manure crops, is worked down at the mid- to full-flowering stage, so land prone to wind erosion will need a cover crop to protect it until the next crop is sown.
Because brassica crops use a lot of nitrogen in the early growth stages, a catch crop of oilseed radish or non-genetically modified canola is used to catch the nitrogen being released from the decomposing vetch. The catch crop is seeded at the end of August and left to grow until freeze up, then worked in the following spring. The following crop is then able to use the nitrogen to its full advantage.
Year 5: Wheat
The nitrogen budget is now more than 60 lb. of nitrogen per acre. AC Barrie wheat makes good use of the nitrogen for producing high yields and protein.
The projected yield will be 35 to 40 bu. per acre, but the low weed population is one of the most outstanding features of the test field. That is credited mainly to the post-emergent harrowing operation. A Lely flexible-tine harrow is used at the one- to two-leaf stage of the wheat and later at the four- to five-leaf stage. The vibrating action of the tines uproots weeds without causing too much damage to the wheat. This technique works best on lighter soils, on wheat compared to oats, where too many plants are destroyed. It also works better on broadleaf weeds compared to grassy weeds.
Since the crop will remove about 60 lb. of nitrogen per acre, the nitrogen budget is now back at neutral.
Year 6: Soybeans
Pulse crops normally contribute as much nitrogen as they consume, so soybeans are a good choice for the final rotation. If the field is row-cropped, then cultivation between the rows works well to control weeds.
In about 20 of the crop rows, Entz planted fall rye within the rows of soybeans to provide a smothering effect on the weeds. It was effective in keeping the weeds out, but this year the rye competed too well with the soybeans and the plants aren’t as vigorous compared to the rest of the field.
Next year, Entz plans to reduce the seeding rate of the rye or use a less-competitive smother crop, such as Italian ryegrass.
An annual cereal is planted in late fall to provide winter cover.
