Managing Nitrogen Inputs Using Petiole Testing

Published in the May 2013 Issue Published online: May 30, 2013 Neal Fehringer and Vance Lungren Jr.
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Today's sugarbeet producers have many tools at their disposal to accurately manage nitrogen. Yet we are still delivering beets with excessive nitrogen and less than acceptable sugar content. This inefficiency in nitrogen costs the producer unnecessary fertilizer dollars and lower sugar content on the production side, as well as increased sugar lost to molasses on the processing side. The challenge for each producer going forward is to look at the factory as an extension of his/her sugar production.

In order to manage nitrogen more effectively, producers and consultants must use soil and petiole sampling data, along with growing degree day, crop health, stand counts, and planting and harvest dates, to manage nitrogen. This will both maximize sugar production in the field, and maximize processing efficiencies in the factory. Petioles are the stems portions of the leaf. Depending upon the laboratory used and test parameters requested, they need the petiole as well as the leaf blade. For nitrogen management only, labs only need petioles. As with soil testing, petiole results are only as good as the sample collected.

A minimum of 16 petioles should be collected from the field or sample area. The correct petiole to be used is the one from the most recently fully expanded leaf. Do not sample within 80 feet of the feet edge (as there may be doubling of fertilizer application in this area), outside the last pivot tower and inside the first pivot span from the pivot point.

Place petioles in a cloth or paper bag so they can breath and not rot. Do not place in a plastic baggie or poly lined bag as they will rot on the way to the lab. In our experience, the nitrogen level wants to be on the line between "High" and "Normal" to produce tons while still having a good sugar level. If the field is targeted for early harvest, then the nitrogen level should be slightly below that line.

However, if the field is flood irrigated then the line needs to be slightly higher than for sprinkler irrigation for early or regular harvest.

Petiole data collected this year, in combination with GDD and plant health data, identified opportunities to add additional in-season nitrogen that allowed the producer to realize added field production without sacrificing processing efficiencies.

Nitrogen management using petiole sampling is proving to be a critical tool as we move forward in sugarbeet production and sugar processing. n

Editor's note: Fehringer is a certified professional agronomist at Fehringer Agricultural Consulting in Billings, Mont. Email nealf@vikingcable.net. Lungren is a beet grower in Wyoming.