Temporal and spatial trends in soil organic carbon stocks following maize cultivation in semi-arid Tanzania, East Africa
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Conversion of native ecosystems to agro-ecosystems influences the amount, quality and turnover of soil organic carbon (SOC). As most agro-ecosystems are not in a steady state in terms of the content of SOC, the time scale and feedback mechanisms of changes in SOC are highly relevant for predicting future soil fertility and potential rates of soil carbon losses or sequestration. This paper focuses on changes in land use linked to measured changes in the distribution of total stocks of SOC and the δ13C signature in the upper 0.5 m of cultivated soils in the semi-arid parts of Tanzania. Based on documented land use changes since 1950s using remote sensing data, 12 sampling sites along two transects were selected to represent semi-natural/natural savannah and maize fields cultivated for up to five decades. Comparisons between sites representing a chronosequence of well-drained soils showed that soils cultivated the last 50 years have in average less than 50% SOC compared to soils which have never been cultivated. Variations between sites were significant and a reduction in SOC could not be established at sites near present or former villages which have received substantial manure despite a long cultivation history or along a chronosequence representing wetter and more fine-grained soils. Spatial variations in land use changes were parameterized based on remote sensing data and successfully validated against sampling sites. Site-specific rates of soil element loss following cultivation were extrapolated to the study area and uncertainties related to scaling up were discussed.
KeywordsSoil organic carbon Tanzania Land use changes Agriculture
This research was conducted as an extension of the Sustainable Agriculture in Semi-Arid Africa (SASA) programme of research originally funded by the Danish Environmental Research Programme. We would like to thank the people of Ilambilole Village for their hospitality and indispensable assistance.
- Birch-Thomsen T (1996) Environment, people and land use. SASA Notes and Working papers, May. Centre for Development Research, CopenhagenGoogle Scholar
- Feldman R (1983) Ismani: agricultural change and the politics of Ujamaa. Monographs in Development Studies No. 10. School of Development Studies, University of East Anglia, UKGoogle Scholar
- Government of Tanzania (2003) 2002 Population and housing census, Tanzania National Website. http://www.tanzania.go.tz/census/iringa.htm. cited 11 June 2005
- Gregersen P (2003) Making the most of it? Understanding the social and productive dynamics of small farmers in semi-arid Iringa, Tanzania. Lund Dissertations in Sociology 54, Lund UniversityGoogle Scholar
- Houghton RA, Boone RD, Fruci JR, Hobbie JE, Melillo JM, Palm CA, Peterson BJ, Shaver GR, Woodwell GM, Moore B, Skole DL, Myers N (1987) The flux of carbon from terrestrial ecosystems to the atmosphere in 1980 due to changes in land use: geographic distribution of the global flux. Tellus 39(B):122–139Google Scholar
- IPCC (2001) Climate Change 2001: the scientific basis. In: Houghton JT, Ding Y, Griggs DJ, Noguer M, van der Linden PJ, Xiaosu D (eds) Contribution of working group I to the third assessment. Report of the Intergovernmental Panel on Climate Change (IPCC). Cambridge University Press, UKGoogle Scholar
- Møberg JP (1999) Basic soil characteristics in the semiarid part of Tanzania in which the SASA project was carried out. SASA Notes and Working Papers. SASA conference November 17–18, 1999, CopenhagenGoogle Scholar
- Ndangalasi HJ (1999) Off-field vegetation study: Ikuwala, Mkulula, Ilambilole and Kalenga Villages, Iringa Rural District, Tanzania. SASA Notes and Working Papers. SASA conference November 17–18 1999, CopenhagenGoogle Scholar
- Ruthenberg H (1980) Farming systems in the tropics. Clarendon Press, OxfordGoogle Scholar
- SAS Institute (1988) SAS/STAT user’s guide, release 6.03 edition. SAS Institute Inc., Cary, NCGoogle Scholar