Ensuring that your crops are rich in nutrients like nitrogen (N), phosphorus (P) and potassium (K) is a crucial aspect of a successful no-till operation. But oftentimes, most of the N, P and K applied to the soil is never absorbed by the crop and does not have a chance to improve crop performance. David Miller, director of education for Advancing Eco Agriculture (AEA), explained in a recent No-Till Farmer webinar why many no-tillers aren’t getting what they expect out of their fertilizers. And it all starts with the label on the package. 

Most fertilizer labels have a series of 3 numbers separated by hyphens on them. But according to Miller, many farmers don’t fully understand what these numbers represent.

“Your first number is always going to be N,” Miller says. “Your second number is P and your third number is K. So just be aware that a higher number of any of those three things is going to indicate that you have a higher concentration of that specific element in that bag of fertilizer."

But even keeping that in mind, it’s not that simple according to Miller. If a bag of fertilizer was labeled 11-52-0, and you apply 100 pounds of that fertilizer, then you’d be applying 11 pounds of N and 52 pounds of P, right? Wrong, says Miller.

“52, or the P number, is actually P2O5, not actual P,” Miller says. “So if you apply 100 pounds of monoammonium phosphate (MAP), it'll give you 52 pounds of P2O5, of which 44% is P. So at 100 pounds, you're going to end up with 22 pounds of actual P.”

MAP is one of the most available forms of water soluble or simple ion P, according to Miller. He also notes that after doing some research, the highest percentage of plant absorption of applied P in the first season was 25%, meaning that 25% of the 22 pounds of actual P is what a no-tiller could expect their plants to take up in the first season at best.

“That's 5.5 pounds of P that you're putting out for your crop,” Miller says. “So what are you spending per ton for 11-52-0? What is that costing you per acre? And how much P are you really getting? 22 pounds of total P in 100 pounds of MAP, of which, at best, you're going to get 5.5 of that taken up by the plant, and at worst, you might get very little taken up. A lot of that is dependent on the amount available calcium that you have because this P in the soluble forms has been denatured through various chemistry interactions that have broken the naturally occurring calcium triphosphate bond.”

As this P is mined in nature, according to Miller, the raw ingredient that these P products started out with is tricalcium phosphate.

“Essentially that means that calcium is attached to this P ion," Miller says. "Through this chemistry process, the P and the calcium are separated, the calcium is taken out, and the P is reacted with a N source and is very heavy. It’s very loosely attached to that, meaning it's very reactive and for any growers who have ever made the mistake of accidentally putting soluble P with calcium, you get an immediate instant reaction.

“When you put the soluble P out in your soil, like for example, in your pop-up or as a broadcast, you are effectively tying up the available calcium that was in your soil. And so now your fertilizer program doesn't have very much calcium and is tying up the available calcium that you had. And therefore, this P fertilizer could actually be a detractor in your overall system and your overall nutrient availability to your plant because of it tying up calcium in the process.”

Miller says understanding the scientific explanation behind the fertilizer label is crucial because growers could likely be reducing their fertilizer usage without sacrificing yield numbers. But in order to successfully make an accurate reduction, a grower has to understand what is in the fertilizer bag behind the meaning of that label. Check out the full webinar below to hear Miller's full explanation for how to reduce fertilizer usage without sacrificing yield numbers.

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