In this week’s Boots In The Field podcast, Ken Ferrie addresses a concern he says has come to his attention several times during the past week. Specifically, a corn grower called his office at Crop-Tech Consulting and said he attended a farmer event where the speaker said because phosphorus prices are too high, he would not put any on fields for the next two years.
“He supposedly hasn’t applied any on his ground for the past two years and has seen no yield loss. Now, my first response is that this presenter is probably being taken out of context,” says Ferrie, Farm Journal Field Agronomist.
When something is taken out of context and run through the local coffee shop talk, information can get off base quickly.
“But we’ve had 10 or 15 people calling the office with the same story, wondering about not putting any phosphorus (P) on fields for two years, so I feel I need to address this,” Ferrie says. “While I still believe the presenter’s being taken out of context, for the purpose of this discussion, let’s say he’s not.”
How Well Does Your Pickup Run Without Gas?
The speaker telling corn growers to not put phosphorus on for two years because he didn’t and had no yield reduction is concerning, Ferrie says. He offers a lighthearted scenario to provide some perspective.
“Imagine you come to one of our winter seminars and I say, ‘Boys, gas prices are too high. I recommend when you go home that you don’t put any gas in your pickup truck. I’ve come to work for two days in a row without putting gas in my truck, and I’ve made it home fine.’ Now for the 90% of you that came to the meeting with a full tank, this advice would work for you. But for the 10% who came in here on a nearly empty tank with the idiot light telling you you’re about to run out of fuel, it might not work so well.
“When the tow truck driver comes to rescue you because you ran out of gas on the way home and he asks, ‘How did you run out of gas? Doesn’t your gas gauge work?’ And you say, ‘Yes, it does, but my agronomist said I shouldn’t fill up with gas that I’d be all right,’ the tow truck driver is going to be shaking his head and wondering about your intelligence level.”
The same is true for arbitrarily deciding to not use inputs like phosphorus for the next two years. Ferrie says growers need to reference their farming gas gauge – their soil test – to determine whether they have adequate fuel to grow the next crop and whether they can cut back on inputs like Phosphorus.
Potential ROI From P Use – The Heart Of The Matter
Here are three examples of available P levels in the field and potential returns-on-investment (ROI) from making an application, based on a Bray 1 soil test:
- With a P level in the 20- to 25-parts per million range, you can expect about a 25% chance of a positive ROI to applying phosphorus.
- When P values drop down to between 10- and 20-parts per million, you can expect a 55% to 60% chance of a positive ROI to applying phosphorus.
- Below 10 parts per million, you have an 80% to 90% chance of a positive ROI to applying phosphorus.
“The top end of these ranges would be true when we have low phosphorus prices and high commodity prices, while the opposite end is true when we have low commodity prices and high phosphorus prices, as we do now,” Ferrie says.
He adds that if you’re growing corn or soybeans, you have to consider both the P removal rates as well as the crop uptake rates.
For a 250-bu. corn crop and a 75-bu. soybean crop, the removal rate is about 140 pounds of phosphorus or 300 pounds of DAP (diammonium phosphate).
“These are the amounts that we know left the field in truckloads of grain,” Ferrie says. “But we had to grow these plants to produce the grain, which are the uptake rates.”
The uptake for 250-bu. corn and 75-bu. soybean crops is about 430 pounds of DAP.
“If you only have enough fuel in the tank (phosphorus) to satisfy removal, yields are going to drop. If your gas gauge is on low end and the idiot light is on and you don’t apply P to these fields, yields will drop,” he says. “But if the whole field is not spread with phosphorus, you might not know the yields drop in areas of it, because P issues are not as visible as nitrogen and sulfur deficiencies.”
It takes about 18 pounds of P₂O₅ to move your “gas gauge” 1 part per million. Not applying for two years could drop your gas gauge by 7 to 8 parts per million.
Now, if you started the season with a soil test showing 30 parts per million, that’s most likely not going to result in a yield reduction. But if you start the growing season with a soil test showing 15 parts per million in the field, you’ve dug yourself into a hole.
Get Ferrie’s full explanation on how to evaluate P use in this week’s Boots In The Field podcast:
P Rates Required To Get Fields Back On Track
To get your “gas gauge” from 7 parts per million back up to 25 parts per million, you’ll need to apply removal rates plus the build rates over multiple years.
“That would take about 150 pounds of DAP per year for removal and another 120 pounds of DAP for build, so 270 pounds of DAP per year for the next six years,” Ferrie estimates.
Many growers do have enough “gas in the tank” that they can pull back on some of their phosphorus. In some cases, complete fields can be pulled back. In other cases, certain zones can be pulled back, but be sure to know what is in your tank in each field.
“Taking a hit in yield because we didn’t look at a working gas gauge is not something you want to be guilty of,” he says. “And guys, we’ll navigate through these tough times. Don’t let emotions, coffee shop talk or some speaker taken out of context, derail your program. Use your tools. Stay the course. Make your plan, follow the plan, and remember your agronomist is just a phone call away.”
Your next read: 7 Tips To Make Your Phosphorus Work For You
