Biogeochemical assessment of resilient humus formations from virgin and cultivated northern Botswana soils.
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.
Almendros
Gonzalo
G
Centro de Ciencias Medioambientales (CSIC), Serrano 115 B, 28006 Madrid, Spain. humus@ccma.csic.es
Kgathi
Donald
D
Sekhwela
Mogodisheng
M
Zancada
María-Cristina
MC
Tinoco
Pilar
P
Pardo
María-Teresa
MT
D001902:Botswana; D002244:Carbon / Q000032:analysis; D055593:Geological Phenomena; D005844:Geology; D006812:Humic Substances / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D012987:Soil / Q000032:analysis*
D006812:Humic Substances; D012987:Soil; D002244:Carbon