MINOT, N.D. — Growing forage is one way farmers can combat increasing problems with herbicide-resistant weeds and annual crop diseases, a University of Manitoba researcher says.
Martin Entz told the Manitoba-North Dakota Zero Tillage Workshop that including forage stands in a crop rotation is making a comeback as a practical option.
Forage was used in the days before commercial fertilizers and herbicides to improve soil fertility and controlling weeds.
But new research, including a survey of 250 farmers in Manitoba and Saskatchewan who are using forage in their crop rotations, is finding it has some modern-day benefits.
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“Observed benefits of short-term alfalfa stands included higher yields in following cereal crops, suppression of annual and perennial weeds, improved soil structure and recovery of deep-leached nitrates,” Entz said in a conference paper.
Using forages to reclaim nitrogen that has trickled too deeply into the soil to be used by annual crops could be a partial solution to a growing environmental problem, he said. The concern is over the potential for nitrates to contaminate water supplies.
But researchers found one year of alfalfa or reed canary grass could significantly decrease the nitrate levels in the top metre (four feet) of contaminated soil. Leaving an alfalfa stand for three years will reclaim nitrates from as far down as two metres.
They also discovered that cereal crops sown into forage land developed deeper root lengths, suggesting the possibility of forage conditioning the soil through “biological tillage.”
Think short-term
Entz said the key phrase for farmers to remember is “short-term” alfalfa stands.
“The yield-enhancing effect of the forage on subsequent crops decreased with forage stands greater than five years.”
Most farmers leave their forage in place twice as long as they should to maximize the benefits. Terminating the forage after three to four years, instead of leaving it for six or seven years, is one way farmers can get the most out of the strategy.
About 12 percent of the arable land in black and grey soil zones of Western Canada is seeded to tame forage crops at any one time. Those are the zones that sweep northward across the Prairies from southern Manitoba through the Peace River regions of Alberta.
Entz said the major factor preventing more farmers from using forages in their cereal crop rotations is the difficulty in getting a stand started and stopped.
But he said management tools such as zero tillage and the use of herbicides to terminate a stand are giving farmers ways to meet those challenges.
Forage seeds are small and must be seeded shallow. In seedbeds prepared by conventional tillage, that increases the risk of poor germination due to lack of moisture. A zero tillage management system improves the moisture conditions and germination.
When it comes to removing the forage stand, Entz said farmers can spray the stand with a herbicide in the fall and then direct-seed a cereal crop into the alfalfa residue the following spring. In ongoing research, that’s proving to be more effective than tillage to remove the forage stand.
“In one study where alfalfa was terminated in mid-September, Roblin wheat yielded 60 bushels to the acre in the herbicide removal treatment and 46 bu. to the acre in the tillage removal treatment.”
