Nitrogen (N) management and N’s impact on yield and protein were discussed by UCCE farm advisor Steve Orloff of Siskiyou County.

“Yield and protein content are the most important factors in determining profitability,” Orloff said. “Nitrogen management is a critical component to achieve that.”

The application of N fertilizer, plus existing N in the soil and water, impact the total N available for plant uptake. Orloff says N accumulation over the season closely follows an S curve. Uptake is very low at the beginning from emergence to tillering. The plant demand for N increases rapidly from tillering to heading, and then flattens out to maturity.

During the tillering to heading period, a plant can uptake 2 pounds of N per day. At the boot stage, the N uptake is close to 80 percent of the total N uptake during the growing season.

How much N to apply is a key question growers often ask Orloff. The answer depends on many factors, including the growth and N uptake dynamics of the crop, the N amount in the soil from the previous crop, yield potential, irrigation water availability, soil properties, weather conditions, and the class of wheat.

“To optimize N for Western-grown wheat yields, 3.3 to 5.0 pounds of N (from soil, water, and fertilizer) per acre is usually required to produce 100 pounds of grain,” Orloff said.

California grain yields have climbed to about 4 tons per acre in many areas. Some growers have achieved 5 tons/acre.

Orloff calculated, “A 4-ton grain crop requires about 260 pounds of N to achieve a 13-percent protein level. About 280 pounds of N per acre is required to produce 14-percent protein.”

For growers striving for five-ton yields, the figure increases to about 325 pounds of N for 13 percent protein, and about 350 pounds N to achieve 14-percent protein.

Orloff urges growers to sample the soil at 1- and 2-foot depths before planting to determine the soil N level. The N level should be considered as part of the total N amount needed to make the wheat crop.

N utilization trials by Orloff last year, and by Mike Ottman of the University of Arizona, suggest that pre-plant-applied N may not be as beneficial as previously thought. Growers may get more N benefit to make high protein when applied later in the season.

cblake@farmpress.com