Control weeds with cover crops
Growing fall rye, winter wheat or sweet clover during April and May of a fallow year greatly reduces weed growth, according to initial research at the Agriculture Canada research centre in Lethbridge.
The extra plant residue prevents erosion and conserves soil moisture.
In Alberta, about 3.5 million acres of farm- land is summerfallowed each year to conserve soil moisture or to control weeds. Cultivation for weed control during fallow, which buries crop residue and normal stubble breakdown, can leave the soil exposed to wind and water erosion. Residue from canola and lentil crops break down rapidly, leaving soil especially vulnerable.
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Cover crops were tested as an alternative to tillage for weed control in fallow systems. Fall rye and winter wheat were seeded on dryland fields at Lethbridge in September 1992, immediately after harvest. No herbicides were used for weed control from September until the crops were killed with Roundup or tillage the following June.
Growing fall rye or winter wheat reduced the amount of herbicide required for weed control in the fallow year by about 50 percent. The additional plant residue would have permitted at least three operations with a wide-blade cultivator without making the soil susceptible to wind erosion.
In a second experiment, flax, peas or mustard were underseeded with sweet clover in May 1993. The sweet clover was killed by mowing or cultivation in June 1994. Sweet clover eliminated almost all weed growth during the fallow year.
Although cover crops used moisture in early spring of the fallow year, the additional crop residue conserved more soil moisture from June to the next spring than bare fallow. Wheat yields in 1994 were similar following cover crop, minimum tillage and zero tillage fallow.
These results are from one fallow-crop cycle. Tests will be continued and extracts from plant residues are being tested for their ability to control specific weeds and plant pathogens.
– Agriculture Canada
