Source: North Carolina State University Cooperative Extension

The North Carolina Department of Agriculture and Consumer Services reminds growers that properly timed spring nitrogen (N) applications are essential to the growth and development of wheat. Assessing N needs now will optimize yield later and is especially important for organic grain growers.

To decide how much spring N to apply, wheat specialists advise submitting two samples of wheat leaves to the department’s Agronomic Services Division for testing. One sample will be used to measure plant nutrient content, the other to measure biomass. Both tests are necessary to obtain the most precise recommendation. The fee is $5 per sample for North Carolina residents and $25 per sample for residents of other states.

“Tissue sampling should be done when wheat reaches Zadoks growth stage 30 (GS-30),” says 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 1/2 inch up the stem.”

Agronomists expect most wheat in the eastern and piedmont regions of the state to reach GS-30 sometime in early to mid-March. Applying N earlier than that could cause tender new growth that would be susceptible to injury during cold snaps. On the other hand, waiting until after jointing increases the chances of damage by application equipment.

“Once GS-30 is reached, growers should immediately collect tissue samples and matching above-ground biomass samples,” McGinnis said. “This is especially true if wheat is lush due to warmer weather or early planting dates. If the crop’s need for N is not met at this time, then tillers will abort and yield will be reduced.”

To tissue sample, cut wheat plants about 1/2 inch above the ground in 20-30 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.

A biomass sample, on the other hand, should contain all the above-ground wheat-plant tissue from one representative, 36-inch section of row. In broadcast fields, collect 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.

Collecting biomass samples has only recently become part of the N determination process. Crop scientist Randy Weisz of N.C. State University developed a method of using biomass weight along with tissue test results to calculate more site-specific N recommendations. His approach 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.

Upon receiving the NCDA&CS plant analysis report, growers should first look for the biomass and N percentage values. These values and certain crop planting details help determine the appropriate N rate, based on Weisz’s interactive tool. This method is explained fully online at www.smallgrains.ncsu.edu/_Pubs/PG/Nitrogen.pdf.

North Carolina growers wanting more information about this method should contact their 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 www.ncagr.gov/agronomi/rahome.htm.