@article{williams_clover_1977,
	title = {Clover {N}-fixation measurement by total-{N} difference and 15N {A}-values in lysimeters},
	volume = {69},
	shorttitle = {Clover {N}-fixation measurement by total-{N} difference and 15N {A}-values in lysimeters},
	abstract = {Abstract:  Assessment and improvement of N fixation by legumes on annual-type range is becoming increasingly important in light of the increasing need for energy conservation.  A comparison was made of two methods assessing N fixation: a simple but crude method by measuring the total-N difference in tops of an N-fixing legume and a non N-fixing grass, and a more expensive method using A-values determined from 15N applications to the same legume and grass species.  Subterranean clover (Trifolium subterraneum) and soft chess grass (Bromus mollis) were grown in field lysimeters (69 cm deep by 36 cm diam.) filled with Josephine loam (Typic Haplozerults, fine loamy, mixed mesic) for 3 years.  Single (100 and 500 kg/ha) and repeated (100 kg/ha) applications of 15N were made and determinations were made of soil and fertilizer N in the plants, soil, and leachate periodically.  The relation between the two methods was strongly linear; fixation (kg/ha) by the A-value method = 50.1 + 0.852 N fixation by difference (r = 0.98, n = 15).  Consequently, previous values cited for N fixation measured by the difference method for winter annual legumes in California may have been underestimated by about 40\%.},
	journal = {Agron. J.},
	author = {Williams, William A. and Jones, Milton B. and Delwiche, C. C.},
	year = {1977},
	keywords = {15nitrogen, 1977, Bromus mollis, Delwiche, C. C., Jones, M. B., Trifolium subterraneum, Williams, W. A., clover, subterranean, isotope, leaching, nitrogen, legumes, annual, lysimeters, nitrogen fixation, estimation, soft chess, soil, Josephine, subclover},
	pages = {1023--1024}
}

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A comparison was made of two methods assessing N fixation: a simple but crude method by measuring the total-N difference in tops of an N-fixing legume and a non N-fixing grass, and a more expensive method using A-values determined from 15N applications to the same legume and grass species. Subterranean clover (Trifolium subterraneum) and soft chess grass (Bromus mollis) were grown in field lysimeters (69 cm deep by 36 cm diam.) filled with Josephine loam (Typic Haplozerults, fine loamy, mixed mesic) for 3 years. Single (100 and 500 kg/ha) and repeated (100 kg/ha) applications of 15N were made and determinations were made of soil and fertilizer N in the plants, soil, and leachate periodically. The relation between the two methods was strongly linear; fixation (kg/ha) by the A-value method = 50.1 + 0.852 N fixation by difference (r = 0.98, n = 15). Consequently, previous values cited for N fixation measured by the difference method for winter annual legumes in California may have been underestimated by about 40%.","journal":"Agron. J.","author":[{"propositions":[],"lastnames":["Williams"],"firstnames":["William","A."],"suffixes":[]},{"propositions":[],"lastnames":["Jones"],"firstnames":["Milton","B."],"suffixes":[]},{"propositions":[],"lastnames":["Delwiche"],"firstnames":["C.","C."],"suffixes":[]}],"year":"1977","keywords":"15nitrogen, 1977, Bromus mollis, Delwiche, C. C., Jones, M. B., Trifolium subterraneum, Williams, W. 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Subterranean clover (Trifolium subterraneum) and soft chess grass (Bromus mollis) were grown in field lysimeters (69 cm deep by 36 cm diam.) filled with Josephine loam (Typic Haplozerults, fine loamy, mixed mesic) for 3 years. Single (100 and 500 kg/ha) and repeated (100 kg/ha) applications of 15N were made and determinations were made of soil and fertilizer N in the plants, soil, and leachate periodically. The relation between the two methods was strongly linear; fixation (kg/ha) by the A-value method = 50.1 + 0.852 N fixation by difference (r = 0.98, n = 15). Consequently, previous values cited for N fixation measured by the difference method for winter annual legumes in California may have been underestimated by about 40\\%.},\n\tjournal = {Agron. J.},\n\tauthor = {Williams, William A. and Jones, Milton B. and Delwiche, C. C.},\n\tyear = {1977},\n\tkeywords = {15nitrogen, 1977, Bromus mollis, Delwiche, C. C., Jones, M. B., Trifolium subterraneum, Williams, W. 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