Site variability effect on field measurement of symbiotic nitrogen fixation using the 15N isotope dilution method |
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| Institution: | 1. Soil Science Unit, IAEA Laboratory, A-2444 SeibersdorfAustria;1. Joint FAO/IAEA Division, P.O. Box 100, Wagramerstrasse 5, A-1400 Vienna, Austria;1. UFR des Sciences de la Nature, Centre de Recherche en Ecologie, Université Nangui Abrogoua, 02 BP 801 Abidjan 02, Côte d’Ivoire;2. Unité de Recherche “Gestion Durable des Sols”, Université Nangui Abrogoua, 02 BP 801 Abidjan 02, Côte d’Ivoire;3. WASCAL Competence Centre, 06 BP 9507 Ouagadougou 06, Burkina Faso;1. Asian School of the Environment, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore;2. Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, 90187, Sweden;3. New Zealand Natural Beef and Lamb Limited, Ruakura Research Centre, Private Bag 3123, Hamilton, 3240, New Zealand;1. Department of Soil Science and Soil Protection, Division of Biochemistry, Faculty of Agriculture and Biotechnology, UTP University of Science and Technology, Bernardyńska 6 St., Bydgoszcz 85-029 (Poland);2. Department of Agrotechnology, Faculty of Agriculture and Biotechnology, UTP University of Science and Technology, Kordecki 20 St., Bydgoszcz 85-225 (Poland);1. Department of Agricultural Sciences, Alma Mater Studiorum University of Bologna, Viale Fanin 40, Bologna, Italy;2. Institute for Microbiology, University of Innsbruck, Technikerstraße 25, A-6020, Innsbruck, Austria;3. Research Centre for Agriculture and Forestry, Laimburg, 39040 Ora/Auer, BZ, Italy;1. School of Atmospheric Sciences, Sun Yat-sen University, Key Laboratory for Tropical Atmosphere-Ocean System, Ministry of Education, Zhuhai, 519082, China;2. Key Laboratory for Urban Habitat Environmental Science and Technology, School of Environment and Energy, Peking University Shenzhen Graduate School, 518055, Shenzhen, China;3. Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 519000, China;4. Department of Civil and Environmental Engineering, National University of Singapore, 1 Engineering Drive 3, Singapore, 117580, Singapore |
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| Abstract: | The sensitivity of the isotope dilution method involving the application of 15N-enriched fertilizers to estimate symbiotic N2 fixation in legumes under field conditions is analysed with respect to the variability of atom% 15N excess in the fixing and non-fixing (reference) crops. Field data collected along a 96 m transect with 63 plots split into two strips, one sown with ryegrass and the other with alfalfa, showed that the sensitivity of the methodology increased with the level of fixation. The results further showed that the sensitivity of the 15N isotope dilution method for estimating N2 fixed can be greatly improved by selecting fairly homogeneous sites, although use of a heterogenous site is quite practicable if the non-fixing reference crop is sited reasonably close to the test plots. Errors associated with mismatch between reference and fixing crops or heterogeneity of site become smaller as the amount of fixation increases. The data also revealed that relative comparisons of N2 fixing abilities of legume treatments based on their 15N enrichments may not be valid for soils with highly variable N content. Under such circumstances, the use of a reference crop sited close to each legume treatment is necessary. |
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