Soil erosion from shifting cultivation and other smallholder land use in Sarawak, Malaysia

Department of Agricultural Sciences, Faculty of Life Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark
Agriculture Ecosystems & Environment (Impact Factor: 3.4). 05/2008; 125(1-4):182-190. DOI: 10.1016/j.agee.2007.12.013


The sustainability of shifting cultivation systems and their impact on soil quality continues to be debated, and although a growing body of literature shows a limited impact on, e.g. soil carbon stocks, shifting cultivation still has a reputation as detrimental to the environment. We wished to compare soil erosion from three land use types in a shifting cultivation system, namely upland rice, pepper gardens and native forest. We used two sample sites within the humid tropical lowland zone in Sarawak, Malaysia. Both areas had steep slopes between 25° and 50°, and were characterised by a mosaic land use of native forest, secondary re-growth, upland rice fields and pepper gardens. Soil samples were collected to 90 cm depth from all three land use types, and analysed for various chemical parameters, including texture, total organic matter and 137Cs content. 137Cs is a radioactive isotope derived from nuclear fallout, and was used to estimate the retention of topsoil in the profiles. Soil chemical parameters in upland rice fields, such as extractable cations, pH and conductivity, indicated limited soil transportation downslope, and depletion of cations from upslope samples are most likely caused by leaching and losses via ashes after clearing and burning. The position on slope had no significant effect on soil texture, carbon or P content, indicating very limited physical movement of soil downslope. A soil carbon inventory to 90 cm depth on the three land uses only showed a higher carbon concentration in the top 5 cm of forest and upland rice plots. When corrected for soil density, there was no effect of land use on the carbon inventory. Moreover, the carbon content in the top 30 cm contributed <50% of the total carbon inventory, hence even significant effects of land use on carbon content in the upper soil layers, are unlikely to change the carbon inventory dramatically. 137Cs content in the soil profile indicated largest retention of original topsoil in the native forest plots, and a loss of 18 and 35% of topsoil from upland rice and pepper gardens, respectively, over the past 40 years. When comparing to 30 cm depth, soil loss was 30% from both upland rice and pepper fields. Low 137Cs activity in deeper soil layers rendered a total profile inventory impossible. It is concluded that shifting cultivation of upland rice in the current system is not leading to degradation of soil chemical and physical quality. The soil carbon inventory is not affected by land use in this analysis, due to the contribution from the deeper soil layers.

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Article: Soil erosion from shifting cultivation and other smallholder land use in Sarawak, Malaysia

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    • "137 Cs content, nutrients and soil texture have been widely used as indicators of soil erosion (Zapata, 2003; Mabit et al., 2008). The 137 Cs method was used to characterize the decline in soil quality associated with tillage erosion including decreased soil organic matter (Li and Lindstrom, 2001; De Neergaard et al., 2008), and 137 Cs changes were highly correlated with soil organic carbon (SOC) changes (Li et al., 2006; Martinez et al., 2010). These results point to the applicability of using the 137 Cs technique to understand land use, erosion, and soil carbon interactions. "
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    • "The sampling site in Sarawak (Belaga) was described previously. The samples for the measured data in Sarawak (Padawan District close to Kuching; De Neergaard et al., 2008) were collected from undisturbed plots including sacred forest , protected areas, and fields that had not been cultivated for more than 60 years. The data from the Sarawak (Belaga) are based Table 4 Synthesized list of measured total inventories of 137 Cs at reference sites in Southeast Asia. "
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    • "The traditional land use of the area is swidden cultivation of upland rice using fallow periods of between 5 and 40 years, as well as pepper and rubber. The environmental and socioeconomic aspects of this land use system were intensively investigated from 2001 to 2003 (Bruun et al., 2006; Hansen and Mertz, 2006; Nielsen et al., 2006; de Neergaard et al., 2008; Mertz et al., 2008). A 2011 study documents that since 2002 the area has undergone substantial conversion of traditional land use systems to small-scale oil palm Fig. 1. "
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