They come in waves – products that promise to do more growing for less money.
The waves usually occur when the price of fertilizer moves out of step with commodity prices.
While prices for fertilizers such as nitrogen and phosphorus are lower than the stratospheric highs of 2008, this year’s prices are still stronger than those of the crops they support.
Claims that orthophosphate fertilizers have an economically effective edge over the more available polyphosphates are circulating across North America this season.
Tom Jensen of the International Plant Nutrition Institute in Saskatoon said the messages are generally the same.
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“The ortho form of the phosphorus is more available to the plants than the poly and because of this you can effectively cut your rate of application and still meet the crop’s needs,” he said.
“It’s true, but not in any sort of economically important way and not as it is presented. In fact, what is happening is reducing the phosphorus that is going into the soil to reduce operating costs. It just isn’t being presented to farmers that way …. Price has a lot to do with convincing people that this will work, but there is something else.”
John Lee, a soil scientist from Advise Laboratories in Northwood, North Dakota, thinks he knows what that “something” is.
“It’s the new factor. I think these new fertilizer products, especially orthophosphates, which aren’t new at all, appeal to producers looking for a production edge they have come to expect from other inputs,” he said.
“They see ads for new pesticides and genetics every year. And in some cases there are improvements. Why wouldn’t the same be true for fertilizers?”
The problem is plants need the same nutrition every year, mainly nitrogen and phosphorus.
“Research has shown that we can cut the rates of phosphorus by banding it close to the seed,” he said.
“There aren’t any wonder products that will let us cut the rates like some new pesticides. I wish there were.”
John Heard of Manitoba Agriculture said orthophosphates are marketed to outperform the polyphosphate versions, which isn’t the case under normal conditions.
Jensen said only under the most severe of droughts, when crops are seeded into extremely dry soil, could orthophosphates have a slight advantage.
“The truth is, either form will give you an equal response in your crop,” he said.
Removing some of the water from phosphoric acid produces short chains of orthophosphate, which become linked together to form polyphosphate or long chains.
When the polyphosphate fertilizer is applied to the soil, it mixes with soil moisture and converts to orthophosphate. Most dry phosphorus fertilizers are orthophosphates, while liquids are mainly polyphosphates.
Plant uptake is mainly in the form of orthophosphates.
Jensen said ammonium poly-phosphorus, 10-34-0, is a common liquid fertilizer that contains nitrogen and phosphorus. According to fertilizer maker Agrium, in this popular form of fertilizer the phosphate is 70 percent polyphosphate and 30 percent orthophosphate.
Polyphosphates become orthophosphates when hydrated by soil moisture, but it takes time. Micro-organisms and the phosphatase enzymes that result from plant root activity also support this conversion.
“The time relates to moisture availability and temperature,” Jensen said.
Researchers have found that the conversion from poly to ortho forms after 72 hours was 42 percent at 5 C, 63 percent at 20 C and 84 percent at 35 C.
Jensen said the use of orthophosphates to supply a crop’s need for phosphate is just as effective as the poly form, but reducing rates because the ortho form is more available isn’t scientifically supported.
“If you have been applying P for a number of years to a field, you can probably get away with cutting your rates for a while, living on what is in the (soil) bank, so to speak,” he said.
“But that works with polyphosphates, too.”
Agrologists warn that products are reflecting this effect when they appear to be effective even though lower amounts of phosphate are applied.
Farmers should be aware that any reduction of phosphate “is just that, a reduction in P,” Lee said.
“Over time if you continued to use these products at reduced rates, you would run out of P.”
