Decomposition of plant material as an indicator of ecosystem disturbance in tropical land use systems S. Hauser * , E. Gang, L. Norgrove, M. a Birang International Institute of Tropical Agriculture, Humid Forest Ecoregional Centre, Mbalmayo, Cameroon, IITA- Cameroon, c/o L.W. Lambourn, 26 Dingwall Road, Croydon, CR 9 3 EE, UK Available online 5 February 2005 Abstract We report on an attempt to distinguish cropped from fallowed land and young from old fallow by the rate of decomposition of a standard material, to contribute towards the development of simple, yet reliable indicators of soil quality and agricultural sustainability on tropical soils. In three southern Cameroonian villages, Senna spectabilis leaves and wood were incubated in undisturbed bush fallow of about 4 years, young secondary regrowth of about 12 years and secondary forest of at least 25 years and in the same fallow age class after clearing and cropping. The decomposition of S. spectabilis leaves distinguished fallowed from cropped land throughout a period of 14 to 280 days after incubation, independent of the fallow type that was cleared and the location. Fallow types were distinguished over the same period, with higher leaf mass loss in secondary forest systems than young regrowth and bush fallow. In all cases mass loss followed significant logarithmic functions. Soil chemical properties were not correlated to leaf mass loss. Mass loss from S. spectabilis wood was not suitable to distinguish either undisturbed from cropped or one fallow age class from another. Significant differences between land uses occurred only at the end of the incubation period. Fallow types could not be distinguished from each other. S. spectabilis leaf decomposition may be developed into one component of a soil quality or soil function indicator if decomposition can be linked to crop yields in cleared sites and biomass accumulation in undisturbed sites and other soil properties. D 2004 Published by Elsevier B.V. Keywords: Soil degradation; Soil quality; Senna spectabilis ; Mass loss 1. Introduction Soil quality, soil health and soil function have become prominent research topics (Doran, 2002; Nortcliff, 2002), but there is no well-defined universal methodology to characterize soil quality (Bouma, 2002). Analytical procedures such as standard chem- ical or physical analysis of soil are often not capable of discerning effects of land use change or agronomic practices. There is a need to develop simple, inexpensive and easy to use methods, to quantitatively determine soil degradation (Lal, 1997). In the humid tropics, dslash and burnT crop/fallow rotations predominate and external inputs are rarely 0016-7061/$ - see front matter D 2004 Published by Elsevier B.V. doi:10.1016/j.geoderma.2004.12.037 * Corresponding author. Tel.: +237 2237 522; fax: +237 2237 437. E-mail address: s.hauser@cgiar.org (S. Hauser). Geoderma 129 (2005) 99 – 108 www.elsevier.com/locate/geoderma