Abstract In the present study, soil C and N mineraliza- tion and nutrient availability were compared: (1) in savanna woodland soils under natural acacia vegetation; (2) at termite sites; (3) in degraded woodland where acacias were selective logged for charcoal production; (4) in agricultural fields which were cultivated for 3 and 15 years, and (5) in traditional homestead fields which regularly received animal manure for about 10 years. Soil C and N mineralization dynamics were measured by incubation under controlled conditions for 120 days. Labile and stable soil C and N pools were determined by fitting double-exponential models to the measured cumu- lative mineralization. Selective removal of acacias from the woodland and short-term cultivation for 3 years did not affect available nutrient contents but significantly de- creased total C and N contents and mineralization (P<0.05). Mainly the labile soil N pool decreased during the first 3 years of continuous cropping, whereas after 15 years the stable N pool, total S, available Ca and Zn contents were also depleted. Even after 15 years, howev- er, the decrease of nutrient availability (apart from N) was less severe than that of soil organic matter stability. Additionally, not only the labile but also the more stable soil C and N pools decreased and controlled total miner- alization as determined by the incubation experiments. Homestead fields with manure additions were shown to have elevated soil nutrient and organic matter contents. However, the manure should be mixed into the soil to improve organic matter stabilization. Soil regeneration in degraded savannas and recently cultivated fields might rapidly be achieved, whereas the 15-years-culti- vated fields may require longer fallows to restore soil fertility. Keywords Mineralization · Nutrients · Semiarid tropics · Soil organic matter · Termite mounds Introduction The savanna woodland of Northern Tanzania is increas- ingly deforested for charcoal (Kahurananga 1995) and agricultural production. Agricultural soils usually have lower aggregate stability (Kandeler and Murer 1993) and soil N availability (Mengel 1996) than soils under natu- ral vegetation. However, the impact of land-use conver- sion on soil fertility in the semiarid tropics, such as on the chromic Luvisols of Northern Tanzania, and its tem- poral dynamics are largely unknown. Whereas some in- formation exists about total organic C and N contents of African savanna soils (Birch and Friend 1956; Jones 1973), little is known about the stability of the soil or- ganic matter (SOM). This knowledge is necessary, how- ever, to evaluate the long-term effect of land-use conver- sion in tropical savannas. High losses of SOM can only be replenished in the short-term by application of organic matter such as ma- nure. In the traditional homesteads of the indigenous Masai population in Northern Tanzania, large amounts of animal manure are usually accumulating. In a temperate climate, manure applications usually lead to increased soil C and N contents (Christensen 1988). The degree to which applications of animal manure are sufficient for replenishing soil fertility is not known for semiarid tropi- cal agroecosystems such as in Northern Tanzania. Fur- thermore, the effects of manure additions on SOM stabil- ity under semiarid tropical conditions have not studied up to now. Within the savanna ecosystem, termites impose an important change on the soil environment and can occu- py a large portion of the land (Lee and Wood 1971). Knowledge about the impact of termites on soil fertility is not only important for understanding the ecology of tropical savannas, but also for evaluating the potential and constraints for agricultural production, since they are B. Glaser · J. Lehmann ( ✉ ) · M. Führböter · D. Solomon · W. Zech Institute of Soil Science and Soil Geography, University of Bayreuth, 95440 Bayreuth, Germany e-mail: johannes.lehmann@uni-bayreuth.de Tel.: +1-607-2541236, Fax: +1-607-2558615 J. Lehmann Department of Crop and Soil Sciences, 909 Bradfield Hall, Cornell University, Ithaca, NY 14853, USA Biol Fertil Soils (2001) 33:301–309 DOI 10.1007/s003740000324 ORIGINAL PAPER Bruno Glaser · Johannes Lehmann · Maike Führböter Dawit Solomon · Wolfgang Zech Carbon and nitrogen mineralization in cultivated and natural savanna soils of Northern Tanzania Received: 24 July 2000 / Published online: 2 February 2001 © Springer-Verlag 2001