Oftentimes, finding the right formula for applying fertilizer can be a delicate balancing act for farmers. Apply too much or in the wrong place, you’ve wasted some money. Apply too little or not where it’ll benefit most, and you can lose money by failing to maximize your yield potential.
And as soil fertility expert Don Flaten points out, with prices continuing to climb, it’s more important than ever to be stringent with your fertilizer dollars.
Read Also
Ergot resistance may open new doors for durum on Prairies
Canada’s first durum variety classified as resistant to ergot may expand the wheat’s acreage in parts of Western Canada where it’s not been typically grown.
“Fertilizer that’s overapplied is a waste of resources,” he says. “But if it’s underapplied, then you don’t reach the crop yields you’re hoping for, and you can’t capitalize on these exceptionally high crop prices.”
Flaten, who retired last year after 33 years as a member of the University of Manitoba’s department of soil science, says he believes the high cost of fertilizer means the penalty for overapplying can be severe as well.
“We’ve got this double-edged sword situation, where the combination of high crop prices and high fertilizer prices make it very important to hit the target in terms of the optimum rate of fertilizer,” he says.
The fact that Prairie farmers are coming off of a drought year complicates matters even more.
“One of the most important steps in any fertilizer program is estimating the yield potential of the crop so you can match its nutritional requirements with a combination of the soil’s reserve of nutrients and the applied fertilizer,” says Flaten.
“If you don’t know whether you’re going to get a 30-bushel wheat crop or a 90-bushel wheat crop because your moisture reserves are pretty scarce, that makes the decision even more difficult.”
There can be a silver lining though. Many fields will likely have plentiful soil reserves of nutrients like nitrogen and sulphur due to last year’s drought, which reduced crop growth and nutrient uptake as a result.
“If there wasn’t sufficient rainfall to cause nitrogen to be lost by leaching or denitrification, we end up with, typically, high concentrations of leftover nitrate nitrogen, for example,” says Flaten.
“This means if we capitalize on that going into this year’s crop, we don’t have to apply as much nitrogen fertilizer because there is already a reserve of leftover nutrients.”
Ross McKenzie, who conducted soil and crop research with Alberta Agriculture for 38 years and is currently a Grainews columnist, agrees. He believes most Prairie farmers who saw a significant yield reduction in their cereal and oilseed crops last year “can probably cut their nitrogen fertilizer rates back by 20 to 50 per cent, or perhaps even more.”
Consider soil testing
Nitrogen levels can also vary widely within fields after a dry year, especially those with undulating terrain and variable soils. A field’s management history can also contribute to nutrient variability, Flaten notes.
“If one portion of a field has a different management history — for example, it was in perennial forage or it received manure many years ago — we can see the impact of that, even in situations where the soil itself and the topography seems to be uniform,” he says.
Of course, the best way to know where and how much nutrients are available to crops is to soil test your fields.
McKenzie maintains the more variable the soils or the landscape within a field, the more important it can be to consider soil testing for variable-rate fertilizer applications. He says agronomists can help farmers identify different management zones — upper slopes, mid-slopes, lower slopes and depressional areas, for instance — which can be sampled separately.
“Then you can develop a different fertilizer recommendation or blend for each of those uniquely different areas in your field, and that becomes a much more efficient way to spend your fertilizer dollar,” says McKenzie.
Flaten points out soil testing serves another useful purpose by helping farmers decide where to best grow their crops.
“After a drought like last year in many areas of the Prairies, soil testing can be a very useful tool to guide the selection of crops for different fields,” he says.
“Crops like canola and wheat that use up large amounts of nitrogen can be a more profitable crop to put on a field that’s high in nitrogen (rather) than a legume crop like soybean or lentil, especially in a year when fertilizer prices are high.”
Most farmers prefer to do soil sampling after harvest because there’s more time to make fertility plans and there’s simply too much to do in the short time before seeding. However, there could be a case made for doing some soil testing this spring.
“If you come out of a drought year and you sample in early September, as long as it stays dry (until) freeze-up, you’re not going to see much change,” McKenzie says. “But if you do get some significant rains after you soil sample, then the nutrient status can start to change, particularly nitrogen and sulphur.”
Flaten also sees some benefits to soil testing in the spring, in certain situations.
“The challenge with any kind of spring testing is, first of all, you have a very narrow window between the thawing of the soil and planting, and that makes it quite challenging to squeeze in the sampling,” he says.
“But it can still be helpful, especially in areas which might have excess moisture, like depressional areas of a field or in regions where they had lots of fall rainfall … or there’s ponding in the spring.”
If you’re worried about seeding your crops in time, one strategy Flaten suggests is to soil sample just prior to planting and then apply a moderate rate of nitrogen even though you’re lacking information on nutrient levels. Then, you can do a followup application of nitrogen if soil tests determine it’s needed and if the weather co-operates.
“There are ways of squeezing in spring testing without compromising timely planting of crops, but it is tricky,” says Flaten.
“That’s why the logistics of spring sampling are challenging and, furthermore, applying nitrogen fertilizer after planting will only be effective if you have rainfall to move the nitrogen into the root zone. If the weather stays dry after the nitrogen is applied on the surface of the soil, the fertilizer is not going to be very effective.”
Focus on nitrogen and sulphur
If you do decide to go ahead with some soil sampling this spring, what types of tests should you get?
McKenzie says he believes your basic tests for nitrogen, phosphorus, potassium and sulphur should be sufficient in most cases. He says nitrogen and sulphur are the nutrients you want to pay closest attention to, since they’re much more mobile in the soil than either potassium or phosphorus.
“Typically, phosphorus and potassium are relatively stable. You don’t see a lot of change in those numbers from one year to the next,” he says. “Nitrogen levels can change quite dramatically. That’s the one I’d be most interested in.”
McKenzie says you’ll generally find good sulphur levels at depth in Prairie soils, particularly in the brown and dark brown soil zones, but it’s not uncommon to see sulphur deficiencies in surface soils.
Both McKenzie and Flaten recommend sampling soils down to a 24-inch depth when testing for nitrogen and sulphur.
“There are some people who recommend sampling to shallower depths, but the data we have has shown that doesn’t work very reliably,” says Flaten. He maintains for potassium and phosphorus, sampling surface soil at the zero- to six-inch depth is usually just fine.
McKenzie points out that most soil test correlation research across the Prairies with phosphorus and potassium is with the zero- to six-inch soil depth.
There are also soil tests for other macronutrients like calcium and magnesium, micronutrients, such as copper, iron, manganese, zinc and boron, and soil characteristics like soil pH, electrical connectivity (EC), organic matter (OM), cation exchange capacity (CEC) and base saturation (BS).
For McKenzie, that doesn’t mean you necessarily need them. “When the same locations are soil sampled each year, soil texture, cation exchange capacity and base saturation don’t change and do not need to be analyzed every year,” he says.
“A lot of agronomists and labs, they like to do a whole suite of analyses, and many of those just aren’t required. For example, if a farmer has been doing testing of micronutrients every now and then and seeing that his micronutrients are all adequate, there’s no point in doing that next spring,” McKenzie adds.
“Odds are if we had a drought year, there’s going to be a certain level of nutrient carryover and maybe a bit more release of organic matter, so you’re probably less likely to run into micronutrient problems.”
Flaten says given the high cost of fertilizer, he recommends farmers be conservative with their supplemental applications of micronutrients and to apply them only if they’re required, according to provincial recommendations.
“It’s difficult enough financially to supply adequate N, K, P and S without spending money on nutrients that are unlikely to be required,” he says. “At the same time, if a soil is low in micronutrients, that information is important to acknowledge and deal with that deficiency, just like any other nutrient deficiency.”
Flaten says he believes if producers can manage it, getting a full assortment of soil tests done can be beneficial for their farms as it allows them to track soil health over time.
“Getting a complete analysis is probably a sensible thing to do, because the whole package is not that much more expensive than getting only a few tests done,” he says. “Once the samples are ready to go, the analysis doesn’t take long.
“Taking samples from different parts of your field on a year-to-year basis will supply data for tracking things like organic matter, salinity, pH — measurements that don’t change too much from one year to the next. If you sample them every year, you have a better idea of what general trends you’re dealing with in terms of soil quality,” Flaten adds.
“For example, I know some agronomists and farmers who have been tracking their soils quite carefully over the last 20 or 30 years, and they are noticing that their soil pH is dropping. They started off with soils that were neutral, and now they’ve got soils that are becoming acidic, and they’re having to confront some of those challenges of dealing with acid soils.”
Select the right lab
Cost shouldn’t be the only consideration when choosing a lab for soil testing, McKenzie stresses. You also want to make sure your soil samples are being tested and analyzed the right way, using the same soil test methods year after year for consistency.
Most soil-testing labs in Western Canada, says McKenzie, “tend to be fairly reasonably priced and do a fairly good job.” If the soil samples are going to a lab outside of Western Canada, farmers must ensure they are assessed according to local and regional fertilizer research and recommended fertilization practices and standards for each Prairie province, he adds.
As an example, McKenzie cites the different tests for measuring phosphorus — in Alberta and Saskatchewan, the recommended technique is the modified Kelowna method, but in Manitoba it is the sodium-bicarbonate method, due to differences in predominant soil types in the Prairie region (also see McKenzie’s column on page 18). Producers should ensure the recommended method for their province is used for best interpretation and fertilizer recommendations.
McKenzie says it’s also important to have a trusted and skilled agronomist to work with to help with sampling, lab selection and soil test result analysis.
“You want to make sure the agronomist you’re working with has been very well trained and is very knowledgeable and, hopefully, has at least five or 10 years of experience working with farmers in terms of making fertilizer recommendations,” he says.
McKenzie also recommends choosing an agronomist who specializes in soil fertility and is either a certified crop advisor or is a member of the Alberta, Saskatchewan or Manitoba Institute of Agrologists.
