Becker-Heidmann 1993b

Becker-Heidmann, P. (1993): On-farm optimisation of the biological nitrogen fixation of grain legumes. Final report to the École Supérieur d’Agriculture d’Angers, March 1990 – December 1992



Terminal report on the results of soil carbon isotope analyses of the French-German-Thai cooperation project „On-farm optimisation of the biological nitrogen fixation of grain legumes“, funded by the European Union.

Five soil profiles have been sampled down to their total depth with the thin layer technique (Becker-Heidmann & Scharpenseel, 1986) at the three experimental sites at Savarit (France), Tachiat and Tonsang (Thailand) from the researcher managed plots with no treatment, a total amount of 1100 kg of soil. Organic and inorganic fractions have been separated. More than hundred samples have been analyzed for pH, carbon content, δ13C and 14C activity, Besides, several additional analyses on selected samples have been done by Drachenberg (1992), which are used only partly in this report.
The literature on the different aspects of the relationship between soil organic matter and biological nitrogen fixation with emphasis on soybean-Rhizobium symbiosis has been carefully reviewed.
The carbon isotope data reveal the organic matter status of the soils, especially the input and decomposition pattern due to microbial activity. Taking into account not only the organic matter status but also additional soil characteristics, the suitability of the different soils for Rhizobium inoculated soybean has been predicted. Accordingly, The Tonsang soil is the most suitable, followed by the Savarit soil and the Tachiat soil. The last one needs appropriate soil management and fertilization.
Phosphorus was reported earlier and stated also within this project as a major limiting nutrient essential for biological nitrogen fixation (BNF). The correct fertilization is depending on the knowledge of the available P (and K) in the soil. Therefore, special attention was paid to the different determination methods which were used by the participating groups. A detailed review shows no consistency in the results in the results of the different methods on the same soils. No suggestion could be derived on which method should be used for which soil. We highly recommend further examination.

Drachenberg, I.: Kennzeichnung des Humuszustandes von Böden unterschiedlicher Klimazonen mit Hilfe von Isotopenmethoden. Diplomarbeit, Hamburg, 1992, unveröffentlich.

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