Basal-Area Growth and Reproductive Responses of Thurber Needlegrass and Squirreltail to Weed Control and Nitrogen Fertilization

Abstract

Effects of weed control and added nitrogen were evaluated in terms of basal area growth, number of reproductive culms, seed yields, and test weight and germination of seed from individual plants of squirreltail (Sitanion hystrix) and Thurber needlegrass (Stipa thurberiana) from 1974 to 1979. Basal-area growth of Thurber needlegrass plants continued during the study period but at a reduced rate during dry years. Parts of squirreltail crowns died during dry periods. A reduction in competition by weed control and added nitrogen stimulated basal area growth of Thurber needlegrass, enhanced germination of squirreltail seed, and increased the number of reproductive culms and seed yield of both species, particularly in years of high precipitation. Germination of squirreltail was much greater than that of Thurber needlegrass. Results are discussed in relation to community ecology, range improvement practices, and seed production for commerce.