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Effects of Temperature and Nitrogen Supply on Four Nitrogen Fractions in Barley¹

Distribution of four nitrogen fractions in tops and roots of 4- and 8-week-old barley (Hordeum vulgare L.) plants as influenced by two rates of nitrogen and three ambient temperatures during the latter half of growth period was studied in pot experiments. All plants were initially grown at 15.6 to 18.3 C for 4 weeks under two nitrogen treatments. Temperature variables were established on the plants during the last 4 weeks of growth. Temperatures tested in two sets of experiments were 7.2 to 8.9 C and 15.6 to 18.3 C, and 15.6 to 18.3 C and 26.6 to 27.7 C. Samples were analyzed for total, alcohol-insoluble, alcohol-soluble, and nitrate nitrogen. Highest dry matter was produced at 15.6 to 18.3 C. The 400-mg N/pot yielded more total, alcohol-insoluble, alcohol-soluble, and nitrate nitrogen than the 20 mg N/pot. Yields of total and protein nitrogen in plants were approximately proportional to yield of dry matter, and percent total nitrogen in plants was inversely related to yield of dry matter. Alcohol soluble nitrogen yield was greater in plants grown at higher ambient temperatures in both experiments. In plants supplied with 400 mg N/pot, an above optimum temperature (26.6 to 27.7 C) caused a significant portion of the total nitrogen to be in alcohol-soluble form. A large part of this alcohol-soluble nitrogen was nitrate nitrogen. This alcohol-soluble nitrogen is highly mobile and can be easily translocated to grain. These results corroborate field observations that temperatures above 27 C during the heading stage of barley plant restrict grain yields, even though protein percent remains high.

Key Words: Total nitrogen • Alcohol-insoluble and alcohol-soluble nitrogen • Nitrate nitrogen • Protein content • Malting barley

² Postdoctoral Research Assistant (now Assistant Professor of Soils, Lincoln University, Jefferson City, Mo.) and Professor of Soils, respectively, North Dakota State University, Fargo, N.D.

Received for publication August 21, 1972.