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How to know when you need a preplant N test

Nitrogen costs are high this spring, a situation that has many farmers looking for ways to apply only the nitrogen their crops really need as a way to maximize the economic benefit. A preplant N test could help you answer the question of how much nitrogen to apply this spring.

In an Extension factsheet, University of Missouri Agronomists John Lory and Peter Scharf say as a supplement to the standard soil test, a preplant N test at a depth of two feet will measure the fertilizer value of inorganic N (nitrate N + ammonium N) in the soil.

They note the preplant N test is not recommended under typical weather conditions on cornfields receiving all nitrogen as spring applied fertilizer. They do recommend it in springtime in the following situations:

- On fields that have received manure anytime since the previous summer.

- On fields that have a history of heavy manure applications.

- Following a drought year on fields with a high potential for carryover of fertilizer N.

- Following fall and early-spring fertilizer applications where excessive rainfall may have caused losses of fertilizer N.

Learn more

Complete recommendations and a formula for interpreting the preplant N soil test for cornfields are available in a University of Missouri Extension factsheet Preplant Nitrogen Test for Adjusting Corn Nitrogen Recommendations

A Soil Nitrogen Test Option For N Recommendations with Corn is available from University of Minnesota Extension.

Do you have an agronomy question? Email cheryl.rainford@meredith.com. We'll send some of the most common questions to professionals in the industry and see what they say. Look for answers in upcoming Agro-Connect Ask the Experts columns.

Nitrogen costs are high this spring, a situation that has many farmers looking for ways to apply only the nitrogen their crops really need as a way to maximize the economic benefit. A preplant N test could help you answer the question of how much nitrogen to apply this spring.

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