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How to Sort Soil Fertility Claims

Make sure agronomics drive fertilizer and crop additive buys.

A university soil scientist once told me of a farmer friend who consistently padded profits by being on the leading edge of technology.

In one area, though, he delved into the bleeding edge by adding magical yield-boosting fertilizers and crop additives. These products included liquid starter fertilizers more plant available  than conventional ones. He dabbled in fertilizer packages that teamed vital nutrients like nitrogen (N), phosphorous (P), and potassium (K) with generous amounts of every micronutrient imaginable for his rich southern Minnesota soils. He even toyed with biological products that purportedly keyed plant processes. 

In his case, disappearing dollars were the only magic created when these products didn’t work as advertised.  

“Gosh, why didn’t you tell me about this?” asked the soil scientist friend. “I have reams of research showing these products just waste your money.” 

“I know that,” the farmer said sheepishly. “But sometime, one of them is going to work, and I don’t want to be left behind.”

Soils just aren’t sexy

That’s understandable. It is true, too, that some multifaceted fertilizer and crop additive packages may fit your farm. Just make sure you buy them when they make agronomic sense. 

“Most farmers know how to drop a transmission out of a tractor,” says David Franzen, North Dakota State University Extension soil specialist. “Others are really good marketers. Universally, though, the things that continue to mystify farmers the most are soils and fertility and plant nutrients.”

Maybe it’s just that studying soils and soil fertility isn’t as sexy as other agricultural areas. “When you go to elevators and fertilizer plants, there are lots of agricultural economics majors making agronomic recommendations, most of whom have never taken a soils course,” he says. “Farmers will come in and rely on them for recommendations. They will say to farmers, ‘Have you heard about this product that has everything you need in it?’ ”

Meanwhile, soil tests that cost $2 to $3 per acre often go ignored for an unnecessary product costing an extra $10 per acre. 

“I will never understand that,” says Franzen. 

Scant regulation helps key such claims. Pesticides endure years of company testing before firms submit them to federal and state regulators for approval. After they clear these channels, odds are high the pesticides will deliver as promised. 

Not so with fertilizer and crop additive products.  

“In most states, a company just needs one successful trial (out of 100 or more) to get a label,” says Franzen. “Once it is in the door and gets a label, no one ever gets thrown out.” 

Scrutinize Starters 

One product area to carefully evaluate are those liquid starter fertilizers that are advertised as being more available to the plant. That’s often the case with orthophosphate starter fertilizers with brand names. When you strip away the brand, these fertilizers often have an N-P-K ratio like 9-18-9 or 6-24-6.

Agronomically, they work well. It’s just that you’ll pay more for orthophosphate starters than you would for conventional polyphosphate starter fertilizers like 10-34-0 because they cost more to make. Numerous studies show no yield edge from their use. 

Typical is the result gleaned from several trials compiled by George Rehm and other University of Minnesota (U of M) soil scientists. In a comparison trial between polyphosphate and orthophosphate fertilizers, 15, 30, and 45 pounds per acre of P205 were applied. The phosphate form had no yield effect across all three rates, says Rehm.  

“All that farmers need to do is look at data to show high-priced starter fertilizers aren’t any better than commodity-type starter fertilizers like a 10-34-0,” says Franzen. “There is no replicated unbiased research that backs up these claims.”

These sales claims often extend to other branded liquid fertilizers, as well. 

“Many liquid fertilizer products sold on a per-gallon basis can be quite expensive on a per-pound-of-nutrient basis,” says Bob Nielsen, Purdue University Extension agronomist. “Yet, they are no more effective or efficient in supplying nutrients to crop plants.” 

Pick Your Battles

Then there are micronutrients.  

“The standard pitch is that a corn plant takes up 14 essential nutrients,” says Franzen. “You have to put all of them on eventually, so why not put them all on today?"

Concentrate first on major plant nutrients. Yearly N applications via manure or commercial fertilizer are almost always needed on corn. P and K levels can quickly be depleted if you forgo them for several years on many soils. 

Sulfur? You may need it for your corn. Since antipollution laws have nixed atmospheric sulfur (S), you need to monitor and correct S deficiencies.

Even that’s not a given. Between 2006 and 2013, only 47% of Iowa State University (ISU) S-rate trials resulted in corn yield increases. In Minnesota, corn yield increases have occurred in loamy and silt loam soils, but they haven’t occurred on silty clay loam-texture soils, says Rehm. 

Odds are lower that you need micronutrients like boron and manganese. 

“In North Dakota and many other states, there is hardly any need for micronutrients,” says Franzen. “They’re already in the soil.

Franzen says many companies told him last year was a tough year for normal fertilizer sales. A bright spot, though, were micronutrients. 

“There is not a lot of cost behind them, and profit margins are large,” he adds. 

When micronutrient deficiencies occur, they mainly occur on sandy, calcereous, or severely eroded soils, says Antonio Mallarino, an ISU soil scientist. Thus, target micronutrients on these types of soils, he says.

Warily Eye Biologicals

The current “sexy” products when it comes to nontraditional soil and crop additives are biologicals, says Franzen. These include growth hormones like auxins, cytokinins, gibberellins, and flavonoids that trigger crop responses. 

One that works well is Cerone, a plant-growth regulator that helps prevent lodging in wheat. It helps key those eye-popping 200-bushel-per-acre wheat yields that European farmers often grow, says Franzen.

 “A lot of these biologicals have done a good job signaling molecules that start certain processes in the plant,” he adds.

In many cases, though, plants already have feedback mechanisms that do this naturally. “So, you’ll spend money on something that is already done by the plant,” says Franzen. 

What To Do? 

Granted, everyone needs to make money. Just make sure you need such products before you buy them.

Start with soil tests. They don’t measure all nutrients accurately, but they’re a good place to start.  

Research questionable products at Iowa State Extension. This website, established by Extension and university soil scientists, lists unconventional products and research reports through a search engine. Type in the product name or a product category (such as ‘starters’ or ‘biologicals’ and the site will list downloadable research studies on the product or product category.

Hiring an agronomist who understands soils and unbiased product data can also aid you.  

Finally, keep this old cliché in mind: If it’s too good to be true, it probably is. 

“If companies just give testimonials and if there is no unbiased backing for the product, be really, really skeptical,” says Franzen. 

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