Fertilize in fall or spring? That’s the question winter wheat growers face every year at seeding time.
There are several advantages to applying nitrogen (N) fertilizer in fall. Usually, N is more economical in autumn than spring, applying it in fall ensures nutrients are immediately available to the crop, and a wet spring can make it difficult for growers to get on their fields to apply fertilizer. That’s true in Manitoba, where a series of wet springs in recent years often delayed fieldwork. Another advantage to applying N in fall is that you don’t have to handle all of that bulk in spring when you’re under time pressure.
There are also advantages to applying N in the spring. Winter wheat plants need a shot of energy as they break dormancy. The earlier N is available to the plants the more likely they are to grow vigorously, especially if they’ve been under stress from the winter.
“The biggest spring management tip I give is, as soon as you can get equipment on the field, get out there and put your fertilizer on because it’s going to need a little shot in the arm,” says Ken Gross, an agronomist with the Western Winter Wheat Initiative. “A little fertility early on will help it get going vigorously.”
If you’re broadcasting N in spring, do it early while the soil is still cool, Gross advises. Applying N too late may limit yield as the seed head for winter wheat is produced very early in the spring. Plants require early nutrition to develop the seed head to its greatest potential.
“On most fields, if you get it [N] on in April, you usually don’t have to worry about protecting it from loss because the soil is cool and you generally get rains in April to wash it into the soil,” Gross says. “If you can’t get there to fertilize the crop prior to the four leaf stage, it’s going to produce a smaller seed head with fewer florets.”
Gross says the recommended practice for wheat is to apply nitrogen in spring before the four-leaf stage, but there are advantages to applying it even sooner.
“Research shows that if you can get fertilizer on earlier, even before the plants start actively growing, you can get a 15 to 30 per cent yield increase.”
Another approach is to split nitrogen fertilizer applications between fall and spring. Doing so limits nitrogen losses to volatilization and leaching in fall while still giving plants the fertility they need. Because nitrogen fertilizer is a winter wheat grower’s most expensive input, no one wants to lose half of it to the environment.
How big should that split between fall and spring applications be? Brian Beres, an Agriculture and Agri-Food Canada research scientist in Lethbridge, suggests the greater application should be in spring, especially if growers are looking to maximize yields.
“Some of the follow-up work we’ve done shows that, as you start to push and intensify the system, the more favourable results will be from a split application where you’re putting the larger balance on in spring,” says Beres.
Beres notes that winter wheat yields up to 40 per cent more than CWRS wheat. Therefore, it requires more nitrogen, especially since winter wheat today yields twice as much as it used to. For that reason, growers should enhance their fertility practices if they’re looking for optimum yields.
It depends on what you want, Beres adds. “If you’re putting a lot of effort into making it a highly intensive crop, then it’s going to pay off to split applications between what’s put down at planting and what’s top dressed in spring,” says Beres. “If you’re more risk averse and shooting for lower yield targets, you’re probably fine putting down the majority of N at planting.”