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How Much Nitrogen Should I Use at Top-Dressing?

By Jenny Carleo and Dr. George Place

Tissue testing is an easy way to know exactly how much nitrogen to put out at top-dress so that we optimize yield and save money on fertilizer applications.

When Should I Sample?

When the growing point has started to move slightly up the stem (growth stage 29). Our target top-dress date is when that plant is at growth stage 30 so be sure to take samples after tillering has finished but before the stem elongates.

How Should I Sample?

We’ll take two different samples that get submitted together: a biomass sample and a percent nitrogen sample. Sample only fresh, living material and remove any dead leaves, previous crop residue or soil before shipping.

Step 1: Lay a yardstick next to a representative row. Cut all of the leaves in that 36″ of row, 1/2″ above the ground and put them into a paper bag labeled “Biomass”. The lab will use this sample to determine what an average biomass is for that length of row in your specific field.

Step 2: Sample about 20 to 30 plants throughout the field. Snip leaves 1/2″ above the ground. Put them all in one separate bag to get the percent nitrogen tissue analysis. Label this bag “percent nitrogen”. This second sample is going to determine the percent nitrogen in the tissue matter;

Step 3: Send samples to the NC Department of Agriculture and Consumer Services lab (or a private lab of your choice). Be sure to let them know your row-spacing on the form, or mention if you broadcast the seed.

Remember that each growing point can ultimately be a wheat head, so if there’s a nitrogen deficiency at growth stage 30 we know we’re going to have lower yields. Tissue testing is the best way to be sure we will get that nitrogen application rate correct.

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