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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    • "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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    ABSTRACT: Soil erosion and loss of soil nutrients have been a crucial environment threat in Southwest China. The land use and its impact on soil qualities continue to be highlighted. The present study was conducted to compare soil erosion under four land use types (i.e., forestland, abandoned farmland, tillage, and grassland) and their effects on soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP) in the Shuanglong catchment of the Dianchi Lake watershed, China. There were large variations in the erosion rate and the nutrient distributions across the four land use types. The erosion rates estimated by 137Cs averaged 2 133 t km−2 year−1 under tillage and abandoned farmland over the erosion rate of non-cultivated sites, and the grasslands showed a net deposition. For all sites, the nutrient contents basically decreased with the soil depth. Compared with tillage and abandoned farmland, grassland had the highest SOC and TN contents within 0–40 cm soil layer, followed by forestland. The significant correlations between 137Cs, SOC and TN were observed. The nutrient loss caused by erosion in tillage was the highest. These results suggested that grassland and forestland would be beneficial for SOC and TN sequestration over a long-term period because of their ability to reduce the loss of nutrients by soil erosion. Our study demonstrated that reduction of nutrient loss in the red soil area could be made through well-managed vegetation restoration measures.
    Preview · Article · Feb 2015 · Pedosphere
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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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    ABSTRACT: Low reference inventories of the fallout radionuclide 137Cs in low latitudes may limit its present and future application for studies of soil erosion and sediment redistribution in Southeast Asia. 137Cs reference inventories and concentrations in surface materials measured in nine and five areas, respectively, across Southeast Asia are here reported and reviewed. The compiled reference inventories decrease from north to south. Three global estimates of 137Cs total fallout are also reviewed and compared to the measured data while taking into account factors that affect the fallout estimates and the reference inventory. The results are presented as a schematic regional distribution map of 137Cs reference inventories for the year 2012. A relationship between a reference inventory and topsoil concentration is also provided. The measured 137Cs concentrations suggest that a minimum detectable activity (MDA) less than 0.5 Bq/kg is required for detection of 137Cs activity in topsoils in the lowest reference inventory areas. This sensitivity should allow, at present, 137Cs to be a useful tool for analysis of soil erosion in Southeast Asia, should also be a useful chronometer, and will be a useful tracer at least where the reference inventory is more than 500-600 Bq/m2. This level of MDA has been demonstrated in previous studies to be achievable by gamma-ray spectrometry using non-destructive sample treatment. As the nuclide decays, sufficient will remain to be useful until the middle of this century in most areas in Peninsular Malaysia and southern maritime Southeast Asia, and a few decades more in the rest of the region.
    Full-text · Article · Nov 2013 · Journal of Asian Earth Sciences
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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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    ABSTRACT: Oil palm plantations are spreading rapidly throughout Southeast Asia and in some countries, they are promoted as carbon sinks compared to the swidden cultivation systems that they often replace. However, little is known about the impacts of this land use change on soil organic carbon (SOC) stocks or soil quality. This study uses resampling of archived soil samples to investigate the sensitivity of permanganate oxidizable carbon (Pox-C) concentration to a change in land use from swidden cultivation to small-scale oil palm plantation on an Ultisol in Sarawak, Malaysia. Furthermore, the results of two different methods of calculating SOC stocks are compared – namely the fixed depth approach and the equivalent soil mass approach, which is sensitive to changes in soil bulk density. Results show that using a method that is sensitive to changes in bulk density is important as the soil bulk density increases upon establishment of oil palm. Thus, topsoil carbon stocks significantly decreased 3–8 years after oil palm establishment as measured by the equivalent soil mass approach, but only marginally and insignificantly decreased according to the fixed depth approach. After 15 years of oil palm, carbon stocks were 40% lower according to the fixed depth approach but 50% lower when using the equivalent soil mass approach. Importantly, the resampling of geo-referenced soil gives more consistent data, and lends credibility to the observation of large reductions in SOC stocks. The concentration of Pox-C in the 0–10 cm layer declines exponentially as oil palm plantations age and can serve as an indicator of change in the soil ecosystem brought about by the investigated land use transition. Pox-C is not more sensitive to this change than standard SOC analyses, but it may serve as an inexpensive, fast and field-suitable means of estimating the SOC status of different land use systems.
    Full-text · Article · Sep 2013 · Agriculture Ecosystems & Environment
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