Leguminous fallows improve soil quality in south-central Cameroon as evidenced by the particulate organic matter status L-Stella Koutika a, * , Christian Nolte a , Martin Yemefack b , Rose Ndango a , Daniel Folefoc a , Stephan Weise a a International Institute of Tropical Agriculture, Humid Forest Ecoregional Center, B.P. 2008 (Messa) Yaounde ´, Cameroon b Institut Nationale de Recherche Agricole pour le De ´veloppement, B.P. 2067 Yaounde ´, Cameroon Received 27 January 2004; received in revised form 5 July 2004; accepted 9 September 2004 Available online 2 October 2004 Abstract Three experiments were conducted on three soil types in south-central Cameroon to evaluate the effects of leguminous fallows on soil quality as compared with nonleguminous fallows. Soil quality was assessed by analysing the status of particulate organic matter (POM) fractions (4000–53 Am): (i) at the end of fallow and after cropping of 3-year-old Chromolaena odorata , fallow with C. odorata removed by hand, and Pueraria phaseoloides fallow; (ii) in soil from 1-year-old C. odorata and P. phaseoloides fallow, before and after 6 weeks of growing maize in a pot experiment, which had two treatments: T1= +P ÀN and T2= +N ÀP; and (iii) at the end of a 2-year-old Calliandra calothyrsus and a 2- and 4-year-old C. odorata fallow. Both, the herbaceous (P. phaseoloides ) and tree (C. calothyrsus ) leguminous fallows improved soil quality of a nonacidic Typic Kandiudult and a Rhodic kandiudult . The N content of either the coarse (4000–2000 Am) or the medium (2000–250 Am) POM fraction was increased as compared to the nonleguminous C. odorata fallow. This trend was also found after cropping all fallows. C. odorata fallow is better adapted to improve soil quality in the acidic Typic Kandiudox , than both leguminous fallows. N addition to soil from C. odorata fallow increased maize growth in the pot experiment as well as the weight of coarse POM (cPOM). P addition to soil from P. phaseoloides fallow had the same effect in the Rhodic Kandiudult , while a more pronounced response to P addition was found in soil from C. odorata fallow in the Typic Kandiudult . A negative effect on cPOM weight after P and N addition was mainly found in soil from P. phaseoloides fallow in the Typic Kandiudox . D 2004 Elsevier B.V. All rights reserved. Keywords: P. phaseoloides ; C. odorata; C. calothyrsus ; Fallow management; Organic matter fractionation; Tropical soils 1. Introduction In shifting cultivation systems of the humid tropics, the soil productivity of the inherently infertile soils is maintained through a long fallow cycle in which soil nutrients and organic matter are recycled by the self- 0016-7061/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.geoderma.2004.09.009 * Corresponding author. Present address: Universite ´ Libre de Bruxelles, Laboratoire de Ge ´ne ´tique et Ecologie Ve ´getales, Chaus- se ´e de Wavre 1850, B-1160 Brussels-Belgium. Fax: +32 2 650 9170. E-mail address: ls _ koutika@yahoo.com (L.-S. Koutika). Geoderma 125 (2005) 343 – 354 www.elsevier.com/locate/geoderma