In 1998, he joined ZEF where he assigned a Ph.D.-study on biological nitrogen fixation in secondary and primary forests of Central Amazonia. He is expected back at ZEF April 2001. Methodological problems, notably the high variability encountered in spontaneous vegetation, have so far impeded conclusive knowledge of BNF in this environment. This research attempts to assess in which phase of successional development BNF takes place, using the 'd15N natural abundance' method. 25 on-farm sites on infertile Oxisol and fertile 'indian black soil' were selected and represent 5 chronosequences of secondary vegetation and 8 primary forest sites for comparisons.
Preliminary results indicate a major importance of legume lianas in early stages of succession.