Time to Submit Wheat Tissue Samples for Spring Nitrogen Needs

— Written By Molly Hamilton

RALEIGH – The N.C. Department of Agriculture and Consumer Services reminds growers that properly timed spring nitrogen applications are essential to the growth and development of wheat. Assessing nitrogen needs now will optimize yield and economic return later, and is especially important for organic grain growers.

To decide how much spring nitrogen to apply, growers should submit a wheat sample to the NCDA&CS Agronomic Services Division for plant tissue testing.

“Tissue sampling should be done when wheat reaches Zadoks growth stage 30  (GS-30) because this is the most important time to apply nitrogen,” said Michelle McGinnis, the division’s field services chief. “To determine growth stage, wait until wheat begins to stand up tall and straight. Then pull several plants, split the stems from the top to the base and look for the growing point. Before GS-30, it will be just above the roots; at GS-30, it will have moved about one-half inch up the stem (Figure 1).”

drawing showing the location of the growing point at gs 30 in wheat

Agronomists expect most wheat in the Eastern and Piedmont regions of the state to reach GS-30 sometime between February and mid-March. “Once GS-30 is reached, growers should immediately collect tissue samples and matching above-ground biomass samples,” McGinnis said. “This is especially true in wet years where pre-plant or residual nitrogen may have leached out of the rooting zone. If the crop’s need for nitrogen is not met at this time, then tillers will abort and yield will be reduced.”

To tissue sample, cut wheat plants about one-half inch above the ground in 20 to 30 representative areas throughout a field. Generally, two large fistfuls of leaves will make a good sample. Remove dead leaves and weeds before placing the sample in a paper bag.

Wheat tissue sampling involves the additional collection of a corresponding biomass sample. A biomass sample should contain all the above-ground wheat-plant tissue from one representative, 36-inch section of row or, in broadcast fields, all the plants from one square yard. Place the sample in a paper bag, and write the sample ID from the corresponding tissue sample and the word “biomass” on the bag (Figure 2).

correct sampling wheat

The first sample will be used to measure the percentage of tissue nitrogen and the second sample measures the plant biomass or dry weight. These two pieces of information together are used to determine the site-specific nitrogen  recommendation. This approach takes into account crop-growth differences due to planting date, row spacing and moisture levels. This method is explained in the chapter on Nitrogen Management in the Small Grain Production Guide.

In addition to the nitrogen analysis, the wheat tissue test includes a full elemental analysis of 10 other essential plant macro- and micronutrients. The fee is $5 per sample for N.C. residents and $25 per sample for samples from other states. There is no additional charge for the corresponding biomass sample.

North Carolina growers wanting more information about this method should contact their regional agronomist, county Cooperative Extension agent or other agricultural adviser. Regional agronomists can offer advice on how to collect and submit tissue and biomass samples and how to interpret and use plant analysis report data. More information is available online at www.ncagr.gov/agronomi/rahome.htm or 919-733-2655.