Clearing up nutrient unknowns on In the Weeds podcast series

Christine Charles<charl122@msu.edu>, Monica Jean<atkinmon@msu.edu> and Paul Gross, Michigan State University Extension - January 19, 2023

“In the Weeds” podcast navigates the uncertain waters of the fertilizer markets with Kurt Steinke, MSU Extension soil fertility specialist.

Wheat — Photo by Monica Jean, MSU Extension.

A variety of uncertainties with the national supply chain, world events and cases of extreme weather will continue the trend of price spikes with fertilizer and nutrient amendments we have seen since 2020. Knowing how to prepare may make or break the budget for the next year. Michigan State University Extension field crop educators Monica Jean (Saginaw Bay region) and Paul Gross (central Michigan region) sat down with MSU soil fertility specialist Kurt Steinke to talk through soil fertility options for the next year in these next two episodes of the Michigan Field Crops Podcast, “In the Weeds.”

Adjusting nitrogen (N) sources and management to be less of a financial strain has been a regular topic of conservation considering current markets. In this podcast, Steinke recommends a variety of techniques to weigh when deciding when and what to buy, like including crop prices and storage costs into the bottom-line equation when deciding when to purchase fertilizer, a reminder to use inhibitors with surface application of urea in case you had a plan to switch N sources, and much more.

The most recently published maximum return to nitrogen (MRTN) N rates for corn yields may also help with making decisions on N rates that are more reasonable for your farm. Steinke also discussed the usability of the MSU fertilizer cost comparison tool to easily compare the prices of multiple N fertilizer options based on the amount you need to apply on your land. With significant advancements to corn hybrids, fertilizer rates needed for N crop removal have decreased across all states and climates. Steinke reminds listeners that “the N efficiency of most corn hybrids means that we are no longer needing a fertilizer replacement of 1.25 pounds of nitrogen per bushel. A 0.8-0.9 pounds of nitrogen per bushel replacement is more realistic” when calculating an N rate for corn removal.

Phosphorus (P) and potassium (K) fertilizer are just as important in the cost equation; what management considerations should be made in response? Steinke underlines the importance of soil testing in determining next steps. Steinke also discusses changes to the newly published Tri-State Fertilizer Recommendations, which may help fertilizer decision making. The new recommendation includes two changes: 1) A recommended but not required buildup period for “deficient” soil test results and 2) the removal of the drawdown period above “optimal” soil test results. These two changes were incorporated to recognize ultimate profitability with fertility decision making. A higher fertilizer rate may be beneficial in nutrient deficient soils to protect against yield loss, but research has shown no agronomic or yield benefit in applying P and K when soils have reached “sufficient” soil test levels. Keeping fertilizer use to just the maintenance rate provides farmers with the flexibility to save money without risking their crop’s nutrient needs.

“Maybe 10-20 pounds P2O5 in starter strip if it’s a rough start to the spring,” Steinke recommends, but beyond that, farmers can rest easier knowing that reductions in fertilizer for the sake of their budget likely won’t threaten yields.

Graph of fertilizer recommendations — The original tri-state recommendations (Figure 1, left) had three distinct recommendations based on soil test values: 1) build-up, 2) maintenance and 3) drawdown. The new tri-state recommendations (Figure 2, right) use a similar but simplified framework in which 1) the build-phase becomes optional at low test levels and 2) the drawdown phase is removed.

Steinke suggests that now may be the time to update yield goals when developing nutrient plans this year. “Go back and look at your average of the past several years, maybe throwing out the drought of 2012, and set your yield potential closer to that,” Steinke says in conversation with Gross and Jean. “Realistic yield goals should be achievable every two to three years.”

“Don’t forget your starter!” Steinke emphases for all commodities, “It won’t pay every year but in not knowing what June or July will look like, applying starter will help set you up as much as possible for the unknown.” “Start right to finish well!” Gross adds in agreement.

Speaking of starting well, would this be the year to start using biologicals? The jury’s still out in terms of published research findings on microbial amendments for nutrient management, but Steinke reviews some important considerations and applications when testing out biologicals on your farm. When soils are within the pH shoulder zones—just below 6 or above 8—biological activity may be inhibited no matter what is applied, Steinke reminds.

Strip trials, rather than applying a product across an entire field, is also key when testing something new. Steinke also pushes growers to directly test the claims when trying a new product. If a new product claims to fix 40 pounds nitrogen (N) per acre and you normally apply 180, you must apply 140 to compare if these biologicals make up the difference, Steinke advises. “There is a time and a place for everything”, said Steinke, and he acknowledges that using biologicals may be helpful in combatting soil borne pathogens.

All in all, testing products on your own field in a side-by-side comparison and looking in published data beyond Google search results will be most informative in making that choice.

Is this the year to use a pre-sidedress nitrogen soil nitrate test? Can you increase N mineralization on your own like most biological products claim? What do we learn from foliar testing? Is there a best way to apply biologicals? How much will pH management matter to fertility planning with this winter and spring’s long-term weather forecast? Listen to the full chemical fertility and biological amendments episodes for the answer to these questions and more!

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