Shifting from alfalfa to a spring seeded annual requires careful management and some rain.
“Replacing alfalfa with a spring crop using spray and direct seeding? It’s the only call I get these days,” said Calvin Yoder, an Alberta provincial forage specialist talking about spring inquiries from farmers.
Yoder said the low price of cattle and hay and the high price of grain and fertilizer are causing farmers to consider shifting acres out of perennial forages that contain alfalfa and into spring seeded grain crops.
“If you waited to kill off your alfalfa until this spring you missed the ideal season to have done it – fall. But you wouldn’t be in that boat all by yourself,” said the agrologist.
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“If it’s pure alfalfa or with little grass in it, then the decision to move from the forage to grain is fairly straightforward,” he said about the economics of such a decision.
With urea prices higher than 60 cents per pound and wheat above $10 per bushel, the profit potential from putting cereals on land that has been in alfalfa for three or more years is far higher than what will be returned from forage feed. Savings in nitrogen costs add up quickly as producers harvest the nutrient sequestered by the perennial legume.
Research at the University of Manitoba and work done by Agriculture Canada has shown that a typical alfalfa stand releases 223 lb. of nitrogen into the soil in the two years after the stand is terminated.
Nitrogen levels from alfalfa appear to peak after three seasons of growth, but soil type, environmental conditions and the presence of grass or weeds that use the stored nitrogen in the field all determine how much may be available to subsequent crops.
Martin Entz of the U of M said despite missing a fall termination window, producers can still reap the rewards of a longer term alfalfa rotation by spraying it out in the spring.
“We know there is a 10 percent yield advantage from spraying out the alfalfa in the fall. However, if it is managed well, you can still see significant savings and good yields from cereals if you want to remove the alfalfa in the spring,” he said.
Research at Agriculture Canada’s Scott, Sask., station showed that an alfalfa crop sucks up 50 millimetres of water in the top metre of soil if it is not terminated in the fall.
“You’ll likely need some starter (nitrogen) put down with the seed, 15 to 30 lb. should do it, depending on your soil test,” said Entz.
Arvid Aasen of Alberta Agriculture said producers should wait until there is some spring top growth before applying glyphosate to the alfalfa.
“Alfalfa is fairly resistant to Roundup. You need to get into that 1.5 litres per acre range if you are going to get good control,” he said.
“You can go with a good broadleaf herbicide depending on what you intend to plant.”
Aasen said the danger of broadleaf herbicides is the effect the chemicals might have on the subsequent crop’s seedlings.
Yoder said glyphosate, at a minimum, would set the alfalfa back, giving a cereal crop a chance to become established.
“Cereals are your best bet as they offer some less expensive herbicide choices for in-crop weed control,” he said.
“Depending on the weather, if it’s cold and wet, or if it’s early in the season, you may only get suppression of the alfalfa.”
Neil Harker of Agriculture Canada in Lacombe, Alta., said having a little alfalfa left in the field might not be the end of the world.
“There aren’t any studies out there to confirm this, however having some alfalfa present will mean that nitrogen is being fixed by the legume. There are other benefits that are less tangible. The positive effect of intercropping a cereal and broadleaf is better known and has several short and longer-term advantages,” said Harker.
“But for that, you will need some moisture to support both crops successfully.”
Agriculture Canada researcher Kelly Turkington often deals with crop plant disease in integrated farming systems.
He said spring-terminated alfalfa crops cause few problems for cereals as the legume roots break down in the soil.
“There will be lots of fungal activity, but it won’t have much of an effect on a cereal crop planted into that soil.”
Broadleaf problems
If a broadleaf crop was sown, it could have some issues with pathogens from the legume breaking down, say researchers.
High percentages of grasses in the forage stand could result in fungi like take-all, scald or net blotch affecting cereals, especially barley.
Agronomists said producers should plan seed treatment for soil-borne disease and for pests such as wireworm.
Entz said the main issues for the subsequent crop are related to nutrients.
“The alfalfa takes two or three times more of these than a cereal crop, so plan for additional (phosphate, potassium and sulfur),” he said.
Aasen said if a cereal is planted, most post-emergent herbicides such as Banvel would further control the alfalfa, especially if tank mixed with 2,4-D or MCPA.
Harker said herbicides containing clopyralid, such as Curtail M, are especially effective with alfalfa, but not all of these herbicides are registered for all cereal crops.
