Current winter barley cultivars have the potential to produce grain yields in excess of 170 bu/ac. Adequate nitrogen availability is essential to optimize grain yields of these modern barley varieties. Twenty field experiments were conducted over three seasons to evaluate barley grain yield response to various combinations of single and split nitrogen (N) application. The experiments were conducted at locations in Virginia and Maryland on Ultisol and Alfisol soils of varying textures. Nitrogen treatments consisted of 0 to 90 lbs N/ac applied at Zadoks' growth stage (GS) 25 followed by N rates of 0 to 120 lbs/ac applied at GS 30. Tiller density at GS 25 and %N in plant tissue at GS 30 were evaluated as predictors for GS 25 and GS 30 optimum N rates. In the 1994-1995 season, a N-uptake study was conducted to determine the amount of N taken up by winter barley with respect to growth stage.

Results from the N-uptake study indicated an N uptake of approximately 30 lbs N/ac at GS 25 followed by an uptake of approximately 70 lbs N/ac at GS 30. Interestingly approximately 70 lbs N/ac was taken up by the barley plants prior to December, indicating the value of barley as an effective N trap crop in a winter rotation, especially with warm Fall temperatures.

Grain yields varied widely among treatments, sites, and years in the N rate and timing study. Yields ranged from 26 to 179 bu/ac in 1992-93, 66 to 159 bu/ac in 1993-1994, and from 30 to 157 bu/ac in 1994-1995. Winter temperatures and spring precipitation were more typical in the 1992-1993 and 1993-1994 seasons. In the 1994-1995 season, mild winter temperatures induced more tillering, and a dry March and April resulted in plants with shorter stems that utilized more N without lodging. A critical N tissue content of 3.5% at GS 30 was determined from tissue tests in 1992-1993 and 1993-1994, which indicated that no additional applied N was required to optimize yields. However in 1994-1995, plants containing 3.5% N at GS 30 required approximately 30 additional lbs N/ac to optimize yields.

Sixteen of the 20 locations responded positively to GS 30 N applications indicating that all or a portion of spring-applied N should be delayed until GS 30. A critical N level of 3.5% in plant tissue should be a useful tool for predicting GS 30 N rates. Tiller counts at GS 25 were evaluated in a climatically atypical 1994-1995 season and, while tiller density appears to be a useful predictor of GS 25 N rates, tiller counts must be evaluated in a more normal season. 

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