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Tissue samples offer nitrogen guidelines for wheat

Tissue samples offer nitrogen guidelines for wheat

• The North Carolina Department of Agriculture and Consumer Services reminds growers that properly timed nitrogen applications are essential to crop development.

Prolonged cold temperatures have delayed wheat development this year. However, a growth spurt can be expected to follow the unusually high temperatures recently experienced in most of the state.

The North Carolina Department of Agriculture and Consumer Services reminds growers that properly timed nitrogen applications are essential to crop development.

“It is getting late for a split nitrogen application, but some fields in central or western counties could still benefit, especially those where plants are just spiking and have only a main stem and one tiller,” said Ben Knox, NCDA&CS regional agronomist.

For growers to determine how much additional nitrogen is needed to finish out the crop, they will have to depend on tissue test results. Knox predicts that growers in the Piedmont will be collecting tissue samples within two to three weeks. In the eastern counties, however, regional agronomist Dianne Farrer is advising her growers to be ready to collect samples very soon.

“Tissue sampling should begin when wheat reaches Zadoks growth stage 30 (GS-30),” Farrer said. “Rate of growth depends on variety, planting date, environmental conditions and location, with wheat in eastern counties reaching GS-30 soonest. When wheat begins to stand up tall and straight, 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.”

“Once GS-30 is reached, growers should immediately collect tissue samples and matching above-ground biomass samples,” Knox said. “This procedure will be new to many growers. Advisors began promoting it last year after research in North Carolina showed it could provide better nitrogen recommendations under most conditions.”

Site-specific recommendations

In the past, North Carolina growers had to rely on spring nitrogen recommendations that had been developed in Virginia. Now they can generate their own site-specific recommendations. This approach is more precise because it takes into account crop-growth differences due to planting date, row spacing and moisture levels.

For wheat grown on large acreages of poorly drained soils, however, growers should consult with an agricultural adviser about whether this method is likely to be useful.

At GS-30, tissue sampling involves cutting wheat plants about one-half inch above the ground from 20 to 30 representative areas throughout a field. In general, two large fistfuls of leaves make a good sample. Dead leaves and weeds should be removed.

Biomass samples, on the other hand, should contain all the above-ground wheat-plant tissue from one representative, 36-inch section of row. In broadcast fields where there are no rows, growers should collect all the plants from one square yard. The sample should be placed in a paper bag, with the sample ID from the corresponding tissue sample and the word “biomass” written on the bag.

Upon receiving their NCDA&CS plant analysis report, growers should first look for the biomass and nitrogen percentage values. Then, they should use an interpretive tool developed by Randy Weisz of North Carolina State University to determine the appropriate nitrogen rate. This tool is available online at

Weisz’ interpretive tool uses the biomass value from the plant analysis report along with planting details, such as the crop’s row spacing or whether it was broadcast, to rank biomass as low, medium or high. Having made that determination, the grower can locate the nitrogen percentage value from the plant analysis report on the appropriate biomass graph to find the site-specific nitrogen recommendation.

North Carolina growers who want to know more about this method should contact their NCDA&CS regional agronomist, county Cooperative Extension agent or other agricultural adviser. Regional agronomists, in particular, can offer advice on how to collect and submit tissue and biomass samples and how to interpret and use plant analysis report data. Contact information is available online at

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