Late Season Stalk Nitrate Test for Corn

Hello I'm Jeff Graybill, agronomy educator with Penn State Extension at Lancaster County Today, I'd like to demonstrate and discuss briefly the proper technique for harvesting a stalk nitrate sample.

It's a tool that we can use to better manage the nitrogen on our farms, particularly in our corn crop.

The earliest that a stalk nitrate test can be taken is at one quarter milk line. Milk line is visible only on the top or tip section of an ear when you break that ear in two.

Here you can see that the milkline has migrated one third of the distance from the outside of the ear toward the center.

After the milkline had migrated to the center and is no longer visible, the corn has reached physiological maturity.

This is evidenced by the formation of the black layer.

Black layer is visible by carefully scraping back the kernal tip.

The test can be performed until approximately three weeks after black layer formation.

You need to collect ten representative plants from each field. Harvest random samples from several sections of a field, taking care to avoid off-types and visibly diseased plants.

I like to pinch the stalk to avoid plants which are developing stalk rot diseases.

An eight inch stalk segment beginning approximately six inches above the ground needs to be harvested for analysis.

I like to use a pruning shears for harvesting samples.

And I've marked my shearers with duct tape at six inches and fourteen inches for an easy yet consistent sample collection method.

Looks like we've got a good, healthy disease free sample.

Now that we've harvested our ten representative samples there's a few more steps we should take before we send them off to the lab. The protocol requires us to cut these sections into smaller, two inch sections. Then they supposed to be put in a paper bag or a breathable container so they will not mold, and send them to the lab.

If you're having to be storing for an extended period of time, say a couple of days or over a weekend, before you would send them to the lab, it's recommended that you put them, again, cut them in a paper bag or breathable container and store them in a refrigerator. It is however, not recommended that you freeze them. This can interfere with the efficacy of the test.

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