title: Biogeochemical assessment of resilient humus formations from virgin and cultivated northern Botswana soils.
abstract: Humic matter in virgin and cultivated Vertisols and Arenosols from Pandamatenga (northern Botswana) has been studied by chemical fractionation and visible and infrared derivative spectroscopies. The in vitro soil respiration was also determined. Soils contained <15 g of total C kg(-1) and displayed scant mineralization activity. In Vertisols, cultivation has led to scarce significant changes in humus characteristics, pointing to a noteworthy resilience of the organic matter. Humic acids showed a very dark color, indicating a large concentration of aromatic structures and stable free radicals. Infrared spectra were featureless and alike. This strong structural stability is also suggested by Curie-point pyrolysis of humic acids, which failed to yield substantial amounts of diagnostic products, mainly in the case of Vertisols. Some unexpected similarities between Vertisols and Arenosols indicate that the influence of external factors on the humic acid formation processes prevails on that of the geological substrate. In Pandamatenga soils only small amounts of recalcitrant C and N forms are sequestered; they represent stable pools relatively independent from short- or medium-term climatic changes or management practices.
authors.affiliation: Centro de Ciencias Medioambientales (CSIC), Serrano 115 B, 28006 Madrid, Spain. humus@ccma.csic.es
authors.forename: Gonzalo
authors.initials: G
authors.lastname: Almendros
authors.forename: Donald
authors.initials: D
authors.lastname: Kgathi
authors.forename: Mogodisheng
authors.initials: M
authors.lastname: Sekhwela
authors.forename: María-Cristina
authors.initials: MC
authors.lastname: Zancada
authors.forename: Pilar
authors.initials: P
authors.lastname: Tinoco
authors.forename: María-Teresa
authors.initials: MT
authors.lastname: Pardo
mesh_terms: D001902:Botswana; D002244:Carbon / Q000032:analysis; D055593:Geological Phenomena; D005844:Geology; D006812:Humic Substances / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D012987:Soil / Q000032:analysis*
chemical_list: D006812:Humic Substances; D012987:Soil; D002244:Carbon