Cultivation-Induced Effects on the Organic Matter in Degraded Southern African Soils

Abstract

We studied quantitative and qualitative changes in soil organic matter (SOM) due to different land uses (reference woodland versus cultivated) on six soils from Tanzania (Mkindo and Mafiga), Zimbabwe (Domboshawa and Chikwaka), and South Africa (Hertzog and Guquka). Structural characteristics of the humic acids (HAs) were measured by Curie-point pyrolysis-gas chromatography/mass spectrometry (P y-GC/MS) and solid-state 13 C nuclear magnetic resonance (CPMAS 13 C NMR) spectroscopy. Significant changes in concentration and composition of SOM were observed between land uses. Losses of organic carbon after cultivation ranged from 35% to 50%. Virgin soils showed large proportions of colloidal humus fractions: humic acids (HAs) and fulvic acids (FAs) but negligible amounts of not-yet decomposed organic residues. The change in land use produced a contrasting effect on the composition of the HAs: a noteworthy "alkyl enhancement" in Mkindo soil and "alkyl depletion" in Chikwaka and to a lesser extent in Dom oshawa. The remaining soils displayed only minor alterations.

Soil organic carbon in agricultural systems of six countries in East Africa – a literature review of status and carbon sequestration potential

“…Woodland-to-cropland conversion generally resulted in an SOC loss (t C ha -1 year -1 ) in the 0-30 cm depth interval of 16.0 (single value), 2.1 ± 2.2, and 0.3 ± 0.8 in the short, medium, and long term, respectively (Table 4; Figure 4). However, the data points were few and varied widely, with SOC loss indicated in some studies (Glaser et al 2001;McDonagh et al 2001;Pardo et al 2012) and SOC sequestration in others in the short (Lemenih 2004) and long term (Nord 2008 grassland to cropland (Birch-Thomsen et al 2007) had a negligible long-term effect on SOC.…”

Effects of Land Use Change on Soil Carbon Storage and Water Consumption in an Oasis-Desert Ecotone

“…Therefore, trade-offs between carbon and water are particularly remarkable in these ecosystems. Human disturbances are mainly represented as land use changes and land management practices, which have been widely investigated with regard to their soil carbon effects under various geographical contexts and climatic conditions across global drylands (Chen et al 2010;Romanya and Rovira 2011;Pardo et al 2012;Santra et al 2012). The findings have revealed a general trend of soil carbon loss following the conversion of natural ecosystems to agricultural uses without proper management (Haghighi et al 2010;Romanya and Rovira 2011;Pardo et al 2012).…”

“…Human disturbances are mainly represented as land use changes and land management practices, which have been widely investigated with regard to their soil carbon effects under various geographical contexts and climatic conditions across global drylands (Chen et al 2010;Romanya and Rovira 2011;Pardo et al 2012;Santra et al 2012). The findings have revealed a general trend of soil carbon loss following the conversion of natural ecosystems to agricultural uses without proper management (Haghighi et al 2010;Romanya and Rovira 2011;Pardo et al 2012). In this respect, local scale comparative studies examining different land cover types based on soil sampling and analyses have been the mainstream approach in the drylands of China and elsewhere (Li et al 2006;Su et al 2010;Raiesi 2012;Saiz et al 2012;De Baets et al 2013;Yang et al 2013).…”

Effects of Experimental Warming and CO2 Concentration Doubling on 13C CPMAS NMR Spectra of Humin in Coniferous Forest Ecosystems of the Eastern Tibetan Plateau in China

“…To date, most studies have focused on the response of humic and fulvic to the environmental changes, due to its relative sensitivity, which provided a more pronounced feedback in the early stage [23]. However, humin, the most relative recalcitrant fraction, is regarded as an important fraction of soil organic matter [24,25], determining the long-term response to climate change. Although it plays an important role in the C sequestration, much uncertainty remains regarding its chemical structure owing to inhomogeneity, structural complexity, and insolubility [26,27].…”