Greg Patterson of A&L Laboratories Canada opens Engine of the Soil Season 2 by showing why a nitrogen rate depends on more than a nitrate test. He walks through the variable rate models his team has built since the mid-1990s: soil moisture, the soil’s holding capacity, estimated nitrogen release, and the balance of potassium, magnesium and calcium. Manitoba agronomist Trevor Thornton adds what he sees in a tight year, when growers cut sampling and variable rate first. Melissa Werkema joins the talk on boron, balance and what agronomists owe their clients. The takeaway for growers is to check what the soil can supply before changing a rate.
You paid for the nitrogen and put it down the tube on the drill. How much of it did the crop actually use? And if you cannot say, what is next year’s rate based on?
Greg Patterson of A&L Laboratories Canada has spent 35 years building nitrogen models for variable rate, starting in the mid-1990s with corn, tobacco and potatoes. In this first live session of Engine of the Soil Season 2, he shows how those models changed, from a heavy calculation to simpler indexes, and why the rate depends on more than a nitrate test. Trevor Thornton, who uses the models with growers in Manitoba, adds what he sees at the farm gate in a year when budgets are tight. Melissa Werkema joins for a frank exchange on boron, balance and what agronomists owe the people they advise.
What’s Inside
• Why Greg says a good year gets only about 45 to 50 percent of applied nitrogen into the crop, and about 15 percent of potassium
• How potassium sets up nitrogen use, including his rule of thumb of about three pounds of potassium for each pound of nitrogen early in the season
• The potassium to magnesium ratio he aims for, about 0.25 to 0.35, and the 10 to 30 percent more nitrogen his models call for when it falls below 0.15
• Why liming without revisiting the nitrogen rate can hurt crop quality, because nitrogen use efficiency rises with calcium base saturation
• Nitrogen holding capacity: why a sandy soil may hold only about 70 pounds of ammonium nitrogen from one application, and when to split it
• Why estimated nitrogen release and soil moisture often matter more than temperature, and what a 2.5 acre grid shows that a bulk nitrate sample hides
• How Trevor’s clients spend variable rate dollars, in his experience: about half the time the same money placed differently, a fifth to a quarter of the time more, and a quarter to 30 percent of the time less
• Cutting costs in a tight year: Greg’s advice to pull back on marginal acres first, and Trevor’s flags-in-the-field method for variable rate without a million-dollar machine
Related Episode:
Your Soil Type Is Costing You Yield
GTF Podcast: Where Does 46% of Your Nitrogen Actually Go?
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