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Published online 1 November 1972
Published in Agron J 64:824-828 (1972)
© 1972 American Society of Agronomy
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Nitrogen Fertilization and Clipping Effects on Green Needlegrass (Stipa viridula Trin.): III. Carbohydrate Reserves1

Larry M. White, Jarvis H. Brown and Clee S. Cooper2

Nitrogen fertilization and frequent clipping have sometimes reduced cool-season grass stands by reducing the carbohydrate reserves. We applied N and imposed clipping treatments to determine their effect on the seasonal variation of total nonstructural carbohydrates (TNC) in stem bases of dryland green needlegrass (Stipa viridula Trin.) during 1969. Ammonium nitrate was broadcast at O, 70, and 140 kg of N/ha in November 1968. Green needlegrass was either left undipped in 1969, or was clipped five times to a 5-cm height at about 21-day intervals from May through July.

Seasonal variation of TNC in stem bases of clipped and undipped plants was similar, but clipped plants had a lower percentage of TNC at all sampling dates. The TNC in nonfertilized, undipped plants decreased from 18 to 14% from growth initiation after winter dormancy (April 5) until after second leaf formation (April 28). The TNC increased after second leaf formation to 19% on May 20 just before boot stage, decreased slightly at inflorescence emergence (May 29), and then increased to 18% at first anthesis (June 9). Following first anthesis, TNC decreased to 9% on July 22 just prior to completion of seed dissemination, increased to 19% in late September, and decreased to 16% by November. The percentage of TNC in clipped plants was 3 to 5 units lower at all sampling dates, and the terminal value in November was 13%. Clipping in 1969 significantly reduced yields in 1970 and tended to reduce yields in 1971.

Nitrogen increased the percentage of TNC in the stem bases during mid-July and again in late autumn, apparently as a result of new tiller development and increased photosynthesis. Nitrogen decreased the TNC only from growth initiation until the second leaf formation. Application of N in November 1968 increased yields in 1969, 1970, and 1971.

Key Words: Nonstructural carbohydrates • N percentages • Residual effects • Seasonal variations

1 Joint contribution from the Northern Plains Branch, Soil and Water Conservation Research Division, ARS, USDA; Montana Agricultural Experiment Station; and Plant Science Research Division, ARS, USDA. Montana Agricultural Experiment Station Journal Series No. 325. Part of a thesis submitted by the senior author in partial fulfillment of the requirements of the Ph. D. degree in Crop and Soil Science at Montana State University, Bozeman, Mont.

2 Range Scientist, Agricultural Research Service, USDA, Sidney, Mont. 59270; Associate Professor of Agronomy, Montana State University; and Research Agronomist, ARS, USDA, Bozeman, Mont. 59715, respectively.

Received for publication April 10, 1972.




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Environmental Quality		 The Plant Genome
Copyright © 1972 by the American Society of Agronomy.