Tissue sampling valuable wheat guide

Just because it's winter, it doesn't necessarily mean your wheat crop needs nitrogen. In tests in North Carolina, field-specific nitrogen application based on tiller density and tissue sampling meant up to 60 fewer pounds of N applied, while maintaining yields in the 50- to 70-bushel range.

The trick lies not in the automatic application, but in checking the stands in late January and early February (Growth Stage 3) and sampling tissue in early March (Growth Stage 4-5) to determine the exact nitrogen needs of winter wheat.

In two years of study, Randy Weisz, North Carolina small grains specialist, has been able to get top yields, reduce nitrogen levels and increase net profit. In some cases, fields where he didn't apply nitrogen to wheat did as well or better than single or split applications. He presented the findings at the joint meeting of small grains, corn and soybean producer associations.

The irony is that only a relative handful of folks are using the tissue sampling method, a practice that costs $4 per field. Instead, they're either applying N all at once or in a split application.

The Agronomic Division of the North Carolina Department of Agriculture and Consumer Services only received 430 tissue samples from wheat fields last season, says Richard Reich, division director.

In his research, Weisz set out to see if field specific nitrogen application really works and asked the question, “Does it really matter?”

At three research sites, Weisz compared single, split, and no nitrogen applications with specific rates based on tiller density and the results of a tissue sample. He tested four different methods of N application: 120 pounds of N in early February; 120 pounds of N in March; no application; and the field-specific rate based on tiller density and a tissue test.

He found the answer to the question rather striking. In short, it does make a difference — in all the right places — to apply nitrogen based on tiller density and a tissue sample.

Last year's frost in mid-April affected the yields, but even that event pointed up the benefits of field-specific application. The fields that had the early application of N had a yield of only 20 bushels per acre due to frost; the March N application, a 59 bushel yield. The field without N yielded 35 bushels, while the field-specific site hit the 50-bushel mark.

The telling part, however, is Weisz used 20 pounds less N on the field-specific application, increasing net returns.

The story was much the same at the Lower Coastal Plain Tobacco Research Station and the Piedmont Research Station. The tissue test called for 30 fewer pounds of N in the lower Coastal Plain and 60 fewer pounds in the Piedmont without reduction in yield.

Fewer pounds of N used meant less money on production costs and a larger net profit, Weisz says. “The field-specific systems always resulted in the highest net return, from $5 to $90 per acre more when N was applied based on tiller density and a tissue sample.”

“Nitrogen application isn't generally a timed practice,” Weisz says. “Most growers are putting it out all in early February and March or they're splitting the application.”

In contrast, knowing the tiller density in early February tells the producer exactly when N is needed and a tissue sample gives the producer an exact idea of how much N is available in the field and makes a treatment rate recommendation.

Tissue samples are generally done in early March (Growth Stage 4-5). Producers can collect 20 to 30 handfuls of wheat and send them to either the state department of agriculture or a private lab. Within 48, hours the producers will know exactly what their wheat N needs are, Weisz says. “If you're not sure, ask your county agent or a regional agronomist with the North Carolina Department of Agriculture.”

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