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Empty soils

Today’s big-yield genetics really are draining the nutrient supply in our soils

The power of today’s corn hybrids and soybean varieties to exceed farmers’ expectations is a testament to the science of plant breeding, and also to the value of selecting the best elite genetics. That farmers in Eastern Canada have been able to push corn yields to 200 bu./ac. and soybeans to 60 bu./ac., even in high-stress growing seasons, has created some pleasant surprises in the past five years.

In the spirit of always having to “pay the piper,” however, growers need to keep asking whether those higher yields can continue without rebuilding soil fertility levels.

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Talk surrounding this question is on the rise as advisers and soil laboratory representatives continue to have conversations with growers regarding response rates to fertilizers. Many farmers are noticing a lack of response to increased applications of different fertilizer compounds, while others are learning they’re getting close to a new limiting factor.

Steph Kowalski was having similar discussions even before she joined the AgroMart Group last summer as agronomy lead. In the past, she created numerous nutrient budgets as a means of drawing a parallel between soil fertility levels and a bank account. For many of her clients, then as now, the discussion always focused on how what they were depositing into the bank wasn’t enough to match what was being taken out by higher-performing corn hybrids and soybean varieties.

“I would add to it that N, P and K are the obvious factors, but we’re also getting more into the micro-world,” says Kowalski. “We’ve caught on to sulphur in the last few years on a wider scale, and we’re starting to look into boron as well.”

Not only with corn and soybeans

Kowalski has also noticed frustration among growers who have applied upwards of 180 lbs. of N and 45 lbs. of S to their wheat, yet have seen little or no response. Although some of that has to do with the performance capability of corn hybrids and soybean varieties, much of it is also a cumulative long-term effect. Growers have cut back on their fertilizer programs, and these hybrids and varieties continue extracting nutrients out of the soil.

Conventional thinking also plays a part in this equation, including rotations, a reluctance to fertilize soybeans, and the rise in the use of cover crops. Kowalski looks at rotation and takes one step beyond the rationale that says, “Corn-soybeans-winter wheat (with red clover) is the standard.” That may be true, but it’s the detail within some of that rotation that can make a difference.

“If you’re baling the straw off from that wheat, that’s removing more potash, or if you’re doing corn silage, you’re removing an immense amount of potash,” says Kowalski. “Rotation is absolutely key, and even factoring in the details of those rotations, of baling straw or that field that was silage, and then with soybean, the lack of organic matter you’re getting from that, it plays a huge role in your nutrient trends.”

Another factor adding to the fertility story is dealing with rented versus owned land, a scenario that Kowalski suggests goes unspoken. It can be hard enough to get farmers who own their land to invest in increased P and K applications; it’s even harder with those holding a one-year lease without any guarantee that they’ll have the land next year.

Kowalski cites the results from a 2013 University of Guelph/University of Manitoba survey of farmers in both provinces, on how they farm owned versus rented land. In all, 53 per cent said farmers take better care of the land they own versus the land they rent, and a majority agreed that farmers would use more manure, fertilizer and complex crop rotations on land they own rather than on land they rent.

Fertilizing soybeans might be another of these “obvious but oblivious” aspects. In past, it was common to say, “Feed your corn and wheat, but don’t worry about soybeans,” since soybeans fix their own nitrogen. But it’s not the nitrogen that they add, but the potash and phosphorus that they extract that is now the issue.

“I know there’s been frustration with soybeans that growers don’t get consistent responses, but soybeans are net users, so it’s important to fertilize the crop,” says Kowalski. The best farms she saw during the driest parts of 2016 were those that had been fertilized, were planted with cover crops in the past, and had high soil organic matter levels that could buffer the crop through those tougher conditions, she says. “They were fed well enough that the soybeans were able to carry through.We need to be feeding these soybeans to counteract that drawdown that we’re seeing.”

Banking on better soils

Drew Thompson has had similar discussions with customers and at company meetings, and he believes the frequency with which he’s having these conversations is on the rise compared to 10 or 15 years ago. Like Kowalski, he uses the banking analogy to indicate to growers where they’re losing fertility levels as they rely increasingly on elite hybrids and varieties.

“When you look at a crop removal budget of corn, soybeans and wheat, we’re probably on average 10 to 15 bu./ac. higher on corn, and hopefully, five to 10 bushels better on soybeans,” says Thompson, market development agronomist with Pride Seeds. “If growers are pulling off higher yields, they need to be putting down more fertilizer.

“If they aren’t, the extra fertility is coming out of the soil.”

Some are upping their fertility, says Thompson, and it showed in some fields in 2017 where yield potential was high thanks to a little more moisture, and growers who were able to manage their soils a little better saw higher yields.

The challenge is that perception doesn’t equal reality, where growers believe they’re putting down enough P or K only to find their rate is still too low. Thompson knows of one grower who applied 250 lbs. of potash on one field in 2016, believing it was more than enough. On closer examination, based on his crop insurance yields, Thompson determined the grower should have applied 350 lbs. of potash for his corn-soybean-wheat rotation.

“If you’re in a tight economic situation and you say, ‘I don’t really have to apply potash, and it’s not going to hurt me from a yield perspective,’ you can get away with that — maybe for a couple of years,” says Thompson. “But ask a grower what they want their soil potash level to be, and they typically want it in the range where it’s not a limiting factor, the point where there is little benefit to adding more. Yet if you look at it in that three-year rotation, you’d have to add almost 300 to 350 pounds of potash in that 0-0-60 product to maintain that level.”

That’s the challenge, where fertility recommendations ask, “What is the economic response?” — or “How much do I need to ensure I maximize my economics?” — versus “How do I maintain the soil level or build it?” Rather than thinking in minimal terms to maintain yield, you shift to thinking about fertility levels to ensure the soil bank is where it needs to be.

Soil test is best

The simple solution to this, despite an economic environment with low commodity prices, is to soil test, even if the results turn out to be overwhelming. It’s similar to the discussion on keeping yield data: When was the best time to start? A decade or two ago. When is the second-best time? Today.

Thompson advocates a greater focus on soil testing, specifically on benchmarking and establishing multi-year datasets. Changes in soil test levels from year to year aren’t apparent, but over a longer term of gathering data, trends begin to emerge and clearer recommendations are formulated.

“It is challenging because it can take many years to see what’s happening,” says Thompson, urging a “bigger picture” perspective. “You need to know what you have in order to make recommendations, but what we really need to do is get farmers to ask themselves, ‘Are you happy with where your soil is? Do you want to build it, do you think you can mine it or do you want to maintain it?’”

When it comes to regular soil testing, Jim Hazlewood has been preaching the benefits of such monitoring for years. As a certified crop adviser and agronomist with Stratford Agri Analysis, he’s concerned that in spite of efforts by soil labs and CCAs, the combination of fertilizer cutbacks and higher-yielding hybrids and varieties is pushing soils on many farms to a tipping point. Farmers who have maintained regular three-year cycles on their analysis have been noticing their soil test P and K levels trending downwards, in spite of fertilizing them at what were thought to be sufficient levels.

“This started before we began getting into these 200 bu./ac. yields,” says Hazlewood. “That’s not to say that the better varieties and hybrids aren’t pulling heavily on the soil, because I believe they are. But perhaps it’s a situation where some of the accepted standards for recommendations might be on the short side.”

There’s little doubt that commodity prices have played a part too, says Hazlewood. Corn prices are down, and soybean prices can’t compensate to any large degree, so farmers are predictably trying to rein in costs, which makes it even harder to sell higher fertilizer rates.

Another part of the soil test issue is understanding the results, where some growers can look at test levels without realizing their impacts. That’s also a part of the challenge for Hazlewood and others, particularly with producers who ask for recommendations, then default to what’s familiar, not what’s needed.

“If you don’t know what you have, you really don’t know what you should be doing,” says Hazlewood. “I’ve been to places where the growers have been completely shocked by the soil tests they got back; they really had no idea how poor things were.”

Hazlewood adds that it’s not a pleasant analogy, yet it’s true that “you have to eat the elephant one bite at a time.” Fertility can’t be the issue that overwhelms a grower.

“Over time, you can build it up — and worse-case scenario — put on enough that you’re not losing more,” states Hazlewood. “Hold your position and feed the crop what it needs, and try not to deplete the soil anymore than it is. If building it back up is not financially practical, at least hold your ground.”

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CG Production Editor

Ralph Pearce

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