When strip-tillers and researchers talk about the benefits of soil microbes populating the root zone of field crops, the conversation generally revolves around more efficient plant use of nitrogen and potential reductions in losses of plant life’s hard-to-hang-onto primary food source.
This year, however, corn growers across the South, parts of the Corn Belt, the Great Plains and California have been growing populations of microbes found to boost the mineralization and cycling of phosphorus (P) — another important macronutrient for plant growth. P is often tightly bound chemically to clay particles in the soil. Because of those bonds, P levels can accumulate faster than crops can access them In farm fields heavily fertilized with poultry or cattle manure — until recently.
We talked early this season with Justin McCoy a senior agronomist for Simplot, part of Innvictis Bioscience, about the company’s recent fielding of two specific growth-promoting rhizobacteria that mineralize bound-up P and transform it into the phosphate form readily useable by growing crops. The product, Revv-Up, contains the bacteria in a long-lasting spore form that “inoculates” the soil to foster populations of the rhizobacteria. Revv-Up can be applied in several ways with dry or liquid applications, in-furrow or at sidedress, to boost available P at critical plant growth stages.
McCoy says the bacteria were originally found growing naturally in a P mine, feeding on the element and mineralizing it there. They were cultured in a laboratory setting, where their ability to improve P cycling became obvious. Researchers took them to the field to test their practical use in nutrient management.
“Our tests in Mississippi, Iowa, Colorado and California consistently showed grain yield increases with Revv-Up on a wide-variety of soils and cropping conditions,” McCoy says.
The agronomist cited results from a large field study in Colorado where feedlot manure had been applied heavily over the years and soil tests showed high levels of P.
“We looked at various sections of that field based on changes in the soil texture, and across the field, we had yield improvements at harvest year in and year out,” he says. “We took half the field and applied Revv-Up, and we used historical grower-standard practices on the other half. We applied no P because P levels were already high. The treated zones showed corn yield increases from 5-12 bushels per acre.”
McCoy says after introduction into the soil, 10-21 days are required for populations of the bacteria to develop.
“We want to see it applied when soil temperatures are above 40 degrees F., so generally burndown applications in those conditions before planting would be appropriate,” he says. “It needs to be out there early in the growing season, so a typical corn sidedress application is about as late as we like to see.”
The product comes in two formulations, Revv-Up, a liquid water-based form, and Revv-Up G, an oil-based form. McCoy says the G formulation allows the bacteria to be impregnated on dry fertilizers and is recommended at a rate of 5 ounces per acre. The standard formulation used with liquid fertilizers, herbicide applications and at sidedress is pegged at 16-32 ounces per acre.
Even in high-P soils, such as the Colorado example, McCoy says strip-tillers can expect an increase in P cycling the first year throughout the season. However, surrounding clay particles often will bind up mineralized P that isn’t used by roots, so Simplot says annual applications are necessary to maintain optimum nutrient cycling.
Simplot worked with crop advisors and growers across their test areas this year with commercial sales of Revv-Up and expects to have it available for sale nationwide for 2024.