Phosphorus (P) is an essential element for early crop growth and root development, however, producers face many challenges managing P in the soil. A recent CropLife Media Group Webinar, “The Great Tie-Up: Phosphorus vs. Your Soil,” presented by sponsor SFP, analyzed the interaction between P and different soil elements, as well as identified ways to improve this important relationship.
Attendees of the Webinar viewed presentations by Dale Leikam, Ph.D., president, Leikam AgroMax, describing the dynamic relationship between P and other elements in the soil, and by Jeff Thompson, regional manager, Iowa, explaining research trials and data with AVAIL Phosphorus Fertilizer Enhancer.
To begin his presentation, Leikam discussed P deficiencies and cautioned attendees most P deficiency symptoms, today, aren’t readily evident by just visually examining crops.
Historically, P and other nutrient deficiencies have been diagnosed primarily via soil test values or a “visual deficiency symptom being observed.” According to Leikam, this is one approach to crop input management that needs to change.
Leikam also made a clear distinction between nutrient availability and nutrient uptake. “They are not the same thing,” says Leikam. “Frequently, when people talk about nutrient availability, many times they are talking about soil test values, and they talk about it as being the availability of that nutrient to the crop, and it may be true in a general sense, but it has nothing to do with the plant’s ability to take up these nutrients. There are many factors affecting nutrient uptake.”
Leikam says moving forward, growers and agronomists need to keep in mind nutrient demand per acre, on a per day basis during critical stages of crop development, as opposed to just relying on soil test results for P.
“The greatest demand for P by the crop, per unit length of roots, occurs very early in the season,” says Leikam. “Right after the crop has used up all the nutrients from the seed, it has a small, little root system and now it has to depend on the soil for nutrients. It’s a critical time for phosphorus nutrition.”
As growers continue to press yields and plant populations higher, one concern is the smaller root system these plants have, per bushel of production, in comparison to crops grown in fields with lower yield potential, notes Leikam.
Another factor to consider is P soil chemistry is “more complex than for other nutrients,” according to Leikam. “When we add P fertilizer to the soil, it reacts with soil cations, like calcium and magnesium, and reverts to much less soluble forms of P,” he says.
Banded applications of P have many advantages in improving nutrient availability to the plant, including:
- Minimizes initial contact with soil “impurities.”
- Reduces soil contact, which increases solution P.
- Delays P “fixation” due to reduced soil contact.
Building on P management, Thompson explained that using AVAIL can increase P availability and presented several slides detailing AVAIL trials conducted in Iowa, as well as other geographical regions throughout the country.
A 2012 Calhoun County, IA, study showed the difference between corn acres treated with standard DAP and DAP treated with AVAIL. “With the ability to take up more phosphorus early in the plant’s life, you can really see the difference between the AVAIL-treated DAP and the untreated,” he says. “You see larger root systems, a bigger plant and more uniformity across the field.”
In a summary of 208 AVAIL corn trials conducted between 2005-2012, including both granular and liquid applications, AVAIL showed an average 9.8 Bu./A yield increase, or a 5.8% average yield increase, according to Thompson.
Another study summary, this one aggregating 13 on-farm corn trials conducted 2005-2010 on fall-applied P treated with AVAIL, showed an average yield increase of 8 Bu./A.