Oct 14, 2019

Prevented planting (PP) acres will have another ‘P’ in their continued story line next year, when these fields come back into production. It’s the P for phosphorus, and a lot of current PP crop ground is going to be very short on this nutrient.

The problem, says Agtegra Agronomy Technical Services Manager Brad Ruden, is that many of these fields will be experiencing fallow syndrome. The combination of standing water and lack of seeded crops reduces the level of mycorrhizae fungi in the soil, resulting in potential phosphorus deficiencies.  

These fungi have a symbiotic relationship with the plants,” explains Ruden. “They get nutrition from the plants in the form of sugars. But they give back by colonizing the root zone and acting as plant root extensions, increasing nutrient absorption, which helps make phosphorus available to crops.”

While nutrients like nitrogen move through the soil profile, phosphorus is not very mobile. Plants intercept phosphorus through strong, biologically-enhanced root systems, aided by mycorrhizae. These beneficial fungi also flourish more on grass crops, like corn. If soybeans were grown in 2018, followed by this year’s idled acres, that two-year lag will have further affected soil biology and reduced the fungi population. 

Without these normal levels of fungi, a different phosphorus strategy has to be implemented. “We’re going to have a real challenge of phosphorus availability in our PP acres, if we don’t pro-actively manage for this,” says Ruden.  Low testing soils will be more affected, but all acres will see some potential issues.

Whether it’s corn or soybeans going in, starter fertilizer for immediate uptake by seedlings must be applied. “Starter is going to be an absolute necessity on these PP acres,” says Ruden. The Prescription Agronomics blends of 8-20-5-4S-.5Zn or A7-23 (7-23-4-1S-.25Zn) will be very effective starters in this situation, along with standard 10-34-0 starter. The general rate will be 5 gallons per acre for corn, and about 2-3 gallons for soybeans.

“That’s enough to get them out of the ground, but it’s not going to be enough near the plants. There will be a need for additional phosphorus,” says Ruden. University of Minnesota research on fallow syndrome reclamation recommends a phosphorus rate of around 30 lb./a near the plants, but that initial starter application is only going to provide about 10-15 lbs. of nutrient underneath the plant.

Ruden suggests a visit with your Agtegra agronomy team to consider additional 2x2 or 3x1 application placements. “We can put on all you’ll need just a few inches away. It will be off the side of the seed row but still available to that upcoming plant,” says Ruden. A phosphorus-availability agent, like Agtegra-proprietary EnhanZe or AVAIL®, is also going to be crucial for getting the most out of your phosphorus strategy, as you manage these former PP fields.

The final piece of the fertilizer strategy is some additional base phosphorus across the field. Consideration of your total phosphorus load, as well as economics, may go into the decision making. “This is a good opportunity to bring up those levels,” says Ruden. “It won’t be immediately corrective, and it will only work if the starters are in there.”

Ruden notes there are some biological products in the marketplace that will directly build mycorrhizae populations. He says the “jury is still out” on their efficacy and success results. But could be considered by some growers, in some situations.

If weather permits, another excellent method for mitigating the effects of fallow syndrome on idled acres is cover crop seeding. Oats and rye and other grass forages will stimulate and restore mycorrhizae levels again. Turnups and radishes, while greatly beneficial, are less efficient at hosting the fungi.

While phosphorus is going to be the most immediate nutrient lacking from a season of PP, Ruden says the entire spectrum of nutrient management needs to be scrutinized after this year. “We had a lot of moisture, so a lot of nitrogen and sulfur will have moved through the soil profile. It’s been a year like no other in so many ways. It will be vital to soil test these fields to see exactly what is available to develop our plan for 2020.”  


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