A study was carried out at Lacombe, Alberta, to develop baseline information on nitrogen recovery, utilization efficiency, and agronomic performance of spring barley. This information may enable us to understand where the inefficiencies of N nutrition may lay and determine strategies to improve nitrogen use efficiency (NUE). Three divergent cultivars, “Manley” (two-rowed, tall, late maturing), “Noble” (six-rowed, mid-height, intermediate maturing), and “Tukwa” (six-rowed, semidwarf, early maturing), were grown under low (0？kg？ha-1), moderate (50？kg？ha-1) and high (100？kg ha-1) rates of applied N fertilization. Both N recovery and utilization efficiency decreased with the increase in rate of applied N fertilizer, and NUE declined from 45？kg？kg-1N under the low N treatment to 33？kg kg-1N under the moderate treatment and 24？kg？kg-1N under the high N treatment. The test cultivars were comparable in N uptake, but Tukwa and Noble were more efficient in their utilization of the N taken up than Manley, particularly under high N. Subsequently, while grain yield of Tukwa and Noble had increased linearly with rate of N fertilizer, the grain yield of Manley showed a declining trend under high N. This implies that, where a high input condition is targeted, improvement in N utilization efficiency may need to be given due consideration. 1. Introduction The cost of N fertilizers, as tied to the cost of natural gas and other contributing factors such as inflation, has sharply increased over the years. For example, in the last two decades alone, the average price for urea, one of the most commonly used forms of N fertilizer, has increased in the United States by about 150%, from $212？Mg？1 in the spring of 1991 to $526？Mg？1 in the spring of 2011 . This increase in cost of N fertilizers has certainly affected profit margins of primary producers particularly for low market value crops such as barley (Hordeum vulgare L.). In addition, there are increasing concerns about environmental pollution of excessive N from agricultural uses. Improvement in nitrogen use efficiency (NUE) may increase net returns to producers and, at the same time, reduce the amount of N lost to the environment and its negative consequences. Nitrogen use efficiency is defined as grain yield per unit of N available to the crop, and it is the product of two primary components: the efficiency of recovery of available N from soil (often called N uptake efficiency, UpE) and the amount of grain yield produced per unit of N taken up by the crop (often called N utilization efficiency, UtE) . Further, UtE
J. I. Ortiz-Monasterio, K. D. Sayre, S. Rajaram, and M. McMahon, “Genetic progress in wheat yield and nitrogen use efficiency under four nitrogen rates,” Crop Science, vol. 37, no. 3, pp. 898–904, 1997.
A. M. Saxton, “A macro for converting mean separation output to letter groupings in Proc Mixed,” in Proceedings of the 23rd SAS Users Group International, pp. 1243–1246, Nashville, Nashville, Tenn, USA, March 1998.
R. Sylvester-Bradley and D. R. Kindred, “Analysing nitrogen responses of cereals to prioritize routes to the improvement of nitrogen use efficiency,” Journal of Experimental Botany, vol. 60, no. 7, pp. 1939–1951, 2009.
S. Muurinen, J. Kleemola, and P. Peltonen-Sainio, “Accumulation and translocation of nitrogen in spring cereal cultivars differing in nitrogen use efficiency,” Agronomy Journal, vol. 99, no. 2, pp. 441–449, 2007.
R. H. McKenzie, A. B. Middleton, L. Hall, J. DeMulder, and E. Bremer, “Fertilizer response of barley grain in south and central Alberta,” Canadian Journal of Soil Science, vol. 84, no. 4, pp. 133–147, 2004.
C. A. Grant, L. E. Gauer, and T. D. Gehl, “Yield response of semidwarf and conventional height barley cultivars to nitrogen fertilizer under varying moisture conditions,” Canadian Journal of Plant Science, vol. 71, no. 2, pp. 361–371, 1991.