Get a head start on next year’s crops with these fertility guidelines, options and pro tips
Many Prairie farmers choose to apply fertilizers to their fields in the fall to save time in the spring — a strategy Farmers Edge agronomist Thom Weir believes makes good sense for a couple of reasons.
“There’s lots of data that shows seeding early has a significant benefit to yield,” he says, adding that for most crops it can be up to two per cent a day.
“If you can … start seeding five days earlier because you don’t have to worry about applying fertilizer, that can, right off the bat, give you around a 10 per cent yield advantage.”
Fall is also often the time when farmers can take advantage of lower fertilizer costs. Weir, who makes a point of tracking prices, says, “Ninety per cent of the time at least, fertilizer is significantly cheaper in the fall than in the spring. So that’s a big plus.”
John Heard, a soil fertility extension specialist with Manitoba Agriculture, says fall fertilizer applications continue to be a well-accepted practice, particularly in Manitoba.
“It works well with our production system here,” he says. “I think our fertilizer use surveys have shown somewhere between 35 and 45 per cent of (Manitoba) farmers put down fall fertilizer, and often (that’s) banded anhydrous ammonia or banded urea.
“We do less zero till than Saskatchewan and Alberta,” Heard says, adding farmers there favour more one-pass seeding and fertilizing.
“We certainly have some of that here. But, for now… rightfully or wrongfully, there’s more tillage being done in Manitoba, and that fall anhydrous ammonia pass sometimes just does the job.”
Of course, fall fertility applications may not be an option if Mother Nature doesn’t co-operate. “Sometimes, you just can’t get it done,” says Heard, noting the unusually wet fall two years ago prevented many western Canadian farmers from laying in fertilizer on time.
“In those cases, then farmers need to develop a Plan B, which is often a spring application of some description, but it may be one they’re not really set up to do with (their) equipment,” he says.
Heard says producers who miss the fall window for fertilizer applications can plan with their agronomists how to meet their fertility needs later. However, if too many farmers are in the same position, he adds, they could face a supply squeeze the following spring.
“A lot of our fertilizer dealers here, too, are not all set up to deliver and apply all the fertilizer in the spring. They really count on this fall application to get a good bunch of the nitrogen out,” says Heard.
Avoid nitrate forms of fertilizer
Nutrient losses are always something to consider when formulating fertility plans. Heard and Weir caution farmers against fall applications of nitrogen in a nitrate form because that’s when it’s most susceptible to losses caused by denitrification, volatilization and leaching.
“We’re not fans of nitrate forms going down in the fall,” says Heard. “(They) are vulnerable to losses right off the hop.”
Heard doesn’t recommend using urea ammonium nitrate for that reason and says better choices for fall applications are anhydrous ammonia, urea or an enhanced efficiency product like ESN or SuperU.
“Ammonium sulphate, generally used as a sulphur source, can provide nitrogen also,” he adds. “(It’s) best put down late in the fall so that nitrogen stays in the ammonium form rather than the nitrate.”
Heard says when it comes to fall fertilizer applications, in-soil banding is generally considered a much better option than broadcasting fertilizer on the soil surface. That’s because banding not only inhibits nitrate conversion but also helps protect fertilizer from immobilization by soil microbes, leaving more nutrients available for plant uptake.
If nitrogen is broadcast rather than banded, it becomes readily accessible to soil microbes, which will use it to decompose straw before the nitrogen is available for use by crop roots, Heard explains. “We want (soil microbes) to decompose straw, but we want them to be second in line behind our crop plants,” he says. “We don’t want them to be first in line.”
Heard says for optimal performance, it’s best that fall-banded fertilizer is not disturbed during spring tillage or seeding operations.
When banding anhydrous ammonia in the fall, it’s important the ground be sealed behind the knives to reduce the risk of nitrogen loss. Heard says the best time to do this is when the soil isn’t too wet or too dry.
“We like to have moist soil ideally to do that, then we have good tilth, meaning those slots can close up nicely and the moisture is there to hold (in) the ammonia also,” he says.
Heard suggests one way to assess soil conditions in a field is to do a test run with the fertilizer applicator to assess how cloddy the soil is and whether it can pack well enough to provide a good seal. Farmers can also do a short pass with anhydrous ammonia and then go back to check whether there’s a strong ammonia smell.
“If it’s unbearable, well, then you stop,” says Heard. “You park, and you wait for better moisture conditions.”
Heard and Weir agree farmers should avoid applying fall fertilizers into wet soils (or fields that are likely to become waterlogged) because that’s asking for trouble.
“If you’ve got a low lying, poorly drained field, that’s not where I put on a fall banding or fall treatment of any sort,” says Weir.
Wait for soil to cool down
Fall-applied nitrogen is best applied banded when soils have cooled down to 5 C, or are at least below 10 C at depth, says Heard. At those temperatures, it will tend to remain in a stabilized form until spring, reducing the risk of ammonia to nitrate conversion and subsequent nutrient losses.
“The cooler it is, the less conversion there is,” Heard says. “When it’s warm, it’s much quicker.”
Heard and Weir say on most Prairie farms, optimal soil temperatures will usually occur around Canadian Thanksgiving.
Heard says farmers may be tempted to apply nitrogen earlier if they have time, particularly if there are attractive pricing offers from fertilizer dealers, but they could end up regretting the decision. “If it was to be put on (too) early, even nitrogen that’s in anhydrous ammonia will convert from the ammonium form to nitrate, and then it is vulnerable to losses.”
Heard says nitrogen losses with early applications don’t always occur, noting that fall banding on warm soils performed as well as — or better — than spring banding at some Manitoba research sites located on well-drained upper slopes. Early banding on warm soils did result in high nitrogen losses in wet conditions with poorly drained, depressional soils, however.
As Heard points out, farmers do have options if they’re planning an early fall fertilizer application when conditions aren’t ideal.
“If a grower makes a decision to apply at what we would normally consider an inappropriate time, now, fortunately, we have some technology that allows him to do some of that while reducing the risk,” he says.
These technologies include nitrification inhibitors, like N-Serve or Centuro for anhydrous ammonia and eNtrench for urea, which contain ingredients toxic to nitrifying bacteria that help keep fall-applied nitrogen in the ammonium form, says Heard. SuperU has both a nitrification inhibitor and a urease inhibitor, which slows the initial conversion of urea to ammonia, he notes.
Weir maintains nitrification inhibitors can be useful in situations where there are variable moisture levels within a field. If there are low spots that aren’t as well drained as the rest of the field, for example, a nitrification inhibitor can be added to delay ammonia to nitrate conversion in those areas.
Weir says controlled-release products like ESN, a urea fertilizer with a polymer coating, are another option for farmers considering early fall nitrogen applications. These products can reduce losses by delaying the initial release of nitrogen and providing it gradually to better match crop uptake needs.
The urea in ESN needs warm, moist conditions in order to leak out of the polymer and into the soil, which physically reduces the amount of product that is available for losses in the fall, especially in dry conditions, Weir notes.
He says some farmers will blend ESN with regular urea and then band it as a way to hedge their bets if conditions worsen after fall applications. “If they lose 50 per cent of the urea, they’ve still got all the ESN, so it’s an insurance program,” he says.
Consider co-banding phosphorus
Putting in phosphorus not only helps replenish fields depleted in the nutrient, but it can also boost yields.
Fall can be a good time to apply phosphorus, since it doesn’t move around as easily in the soil as nitrogen and is less susceptible to losses as a result. It’s also a way farmers can spread out their phosphorus programs, so that what’s being put in at seeding time doesn’t exceed seed-safe rates.
“If they’re putting on fall nitrogen anyway, that’s an opportune time to co-band phosphorus with their nitrogen,” Heard says. “We see that as another gold star practice that doesn’t encumber spring fertilization and reduces risk of damage from you having to put down too much phosphorus with the seed.”
Heard says the dual placement of phosphate with nitrogen will tend to increase the availability of the phosphorus to the following year’s crop due to the acidifying nature of anhydrous ammonia. Banding phosphorus and nitrogen together also keeps the phosphorus under the soil surface so it’s less vulnerable to losses from runoff and snowmelt.
Monoammonium phosphate is a widely used source of phosphorus and nitrogen. Weir says it works well on its own or blended with other products like urea, ESN or SuperU in a banded fall application.
Weir recommends farmers who do this save some phosphorus to put in with the seed row in the spring. Heard agrees. “Certainly, we advocate some starter phosphorus in the spring to provide some nutrition until the seedling reaches those bands,” he says.
By co-banding nitrogen, phosphorus and, if needed, sulphur in the fall, it can make things easier and safer for farmers come spring seeding time, adds Heard.
“Canola crops need sulphur and ammonium sulphate is harsh (when placed) in the seed row of canola,” he says. “If you can co-band your ammonium sulphate, if that’s what you’re using, with your nitrogen in the fall … (that’s a) good spot to put it in.”
Weir maintains some growers are moving away from putting down sulphur at seeding time because of toxicity concerns with ammonium sulphate as well as some handling issues.
“It takes up moisture and can cake in the air drills and stuff like that, so a lot of guys are looking for alternatives,” explains Weir. By applying ammonium sulphate in the fall, he says, this enables farmers to get their sulphur in and a good chunk of their nitrogen out of the way as well.”
Farmers who use ammonium sulphate likely won’t have to apply any more sulphur to their fields for the following three cropping years, Weir adds.
