1. Alef K, Nannipieri P (1995) Soil respiration. In: Alef K, Nannipieri P (eds) Methods in applied soil microbiology and biochemistry. Academic Press Inc., San Diego, pp 214–219
2. Bosshard C (2007) Nitrogen dynamics in organic and conventional cropping systems. PhD dissertation, ETH No. 17329, Swiss Federal Institute of Technology ETH, Zurich, Zurich, Switzerland
3. Bosshard C, Frossard E, Dubois D, Mäder P, Manolov I, Oberson A (2008) Incorporation of nitrogen-15-labeled amendments into physically separated soil organic matter fractions. Soil Sci Soc Am J 72:949–959
4. Cottenie A, Verlod M, Kiekens L, Camerlynck R (1982) Chemical analysis of plant and soil. Laboratory of Analytical and Agrochemistry State University Ghent, Belgium, p 63
5. Danso SKA, Hardarson G, Zapata F (1993) Misconceptions and practical problems in the use of 15N soil enrichment techniques for estimating N2 fixation. Plant Soil 152:25–52. doi: 10.1007/BF00016331