Effects of depth and land cover on soil properties as indicated by carbon and nitrogen-stable isotope analysis

The aim of this study was to evaluate the effect of soil depths (0-30, 30-60, and 60-90 cm) and landcover changes on selected physicochemical properties in soils transformed from a secondary forest status to plantation status for the cultivation of rubber and oil palm aged 5 and 15 years. Soil physicochemical properties; bulk density (Bd), pH, soil organic matter (SOM), total organic carbon (TOC), total organic nitrogen (TON), and their corresponding isotopes; and δ13C and δ15N were determined by conventional methods. The results showed that the content of SOM (3.39%) at 0-30 cm was signifi cantly greater than those of the 30-60 and 60-90 cm depths. The same pattern was demonstrated by the content of TOC and TON. With respect to land use, the secondary forest had signifi cantly greater SOM content than the rubber and oil palm plantations aged 5 years. The same pattern was also observed for the content of TOC and TON by land use. Similarly, the δ13C value of -26.85% was greatest at the 0-30 cm depth, while by land use the oil palm aged 5 years had the greatest δ13C. Conversely, the δ15N value of 4.21% was signifi cantly greater at the 60-90 cm depth compared to the 30-60 (1.78%) and the 0-30 cm (-2.03%) depths. The negative value of δ15N revealed the sources (N was a product of multiple variables such as N fi xation, precipitation, rainstorm, and the use of chemical fertilizers), and the limited nitrogen content in the study area. In conclusion, this study demonstrated that the conversion of secondary forest to plantation enhanced the mineralization of soil organic matter and increased SOC concentrations at the sub soil. Therefore, the conversion of the secondary forest to the oil palm plantations must have resulted in a positive effect by contributing to greater soil organic carbon content

Tracing carbon and nitrogen fluxes in soil of log-over forest and highly degraded area of oil palm plantations using stable isotope analysis

The role of soil organic matter in the world’s climate has become the focus of recent studies, particularly with suggestions by the Kyoto protocol that soils may act as a potential sink for CO2. With approximately 1500 Gt C contained in the upper meter of the world’s mineral soils. Changes in climate and land-use will have significant effects on the carbon budget, particularly with respect to the turnover rate of soil carbon. Conversions of tropical forests in to oil palm plantations may effects on the amount of organic carbon in soil and consequently release the carbon into the atmosphere as carbon dioxide (CO2). For this reason, this study will focus on use of natural abundance level of stable carbon and nitrogen isotopes as tracer of soil organic matter and nitrogen cycling in oil palm plantation with different land history. Furthermore, this work will include identification of relationship between C13 and N15 abundance in vertical soil profile and also the soil C and N concentration. Later the relationship of stable isotopes and heavy metals concentration which used extensively in this area will also be determined. At the end of this study, the selection of best land for oil palm plantation will be established for better environmental justice

Spatial distribution of carbon and nitrogen stable isotope in soil of an oil palm plantation

The conversion of lowland tropical forests to oil palm plantations is known to reduce the amount of soil carbon and nitrogen. However, this has been criticised as the plantations also contribute to a net gain of the soil carbon (C) stock. In this study, carbon and nitrogen stable isotopes techniques was used to confirm the source of carbon stored in plantation soils and to prove the effects of plantation activities on soil organic carbon. The objective of this study was to investigated the total organic carbon (TOC) and nitrogen (TON) content, and δ 13C and δ 15N values of soil in an oil palm plantation at different soil depths: 0-30, 30-60 and 60-90 cm and at different distances ((1.5 m: weeded circle), 3.5 (inter-rows) and 4.5 m (frond heap)) away from the tree base. The results showed that the ratio of soil δ13C and δ15N increased with depth and unusual δ15N value was reported on topsoil 0-30cm, a non-uniform distribution of soil OM (%), TOC (%), TON (%) and C/N ratio in the surface soil among the distances were observed. Negative correlation between δ13C and δ15N and bulk density (Bd) in respect of TOC and TON content were found. Value of δ13C at 0-30, 30-60 and 60-90 cm depths was -26.50, -26.36 and -26.23% respectively. This study conclude that, a low proportion of C was lost from the plantation soil , a long phase of C3 species dominated the soil before the establishment of the oil palm plantation and that frond heaps and large concentration of roots had a significant influence on OM (%), TOC (%), TON (%) and C/N ratio in the surface soil among the distances. The δ15N value in the top soil might be a useful indicator of the source and limited level of nitrogen in the area of study, however, further research is needed to confirm our observations

Distribution, deposition and spatial variability of carbon in soil using carbon and nitrogen stable isotopes

Soil carbon (C) storage has gained much attention in the past decade due to its potentially huge impact on climate change mechanisms. However, there is still a lack of knowledge about the contribution of different C sources to soil organic carbon (SOC) formation, particularly in the subsoil. Land-use conversion to agricultural systems can affect soil C storage in terrestrial ecosystems by altering either the biotic or the abiotic processes involved in carbon cycling, such as the distribution of SOC in size at different depth of profile. The focus of this thesis was to; determine the impacts of land.-use conversion on soil carbon distribution and dynamics, as well as (2) provide an understanding of the sources of C in the investigated site. In this study, the organic carbon (OC) contents and their δ13C and δ15N stable isotopes of three soil profiles (0-30, 30-60 and 60-90 cm) under different land uses in the Selangor State in Southwest Malaysia were analyzed using (i) physical fraction of soil into different particle-size, (ii) natural abundance of the δ 13C and δ15N stable isotopes and (Ⅲ) FTIR spectroscopy. Regarding the effect of land use change on soil chemical and geo-physical properties, a two way MANOVA was used to analyses the data, with respect to spatial and depth variations, with Tukeys post-hoc tests to separate the means. Same analysis was also done for the distribution of SOC and (δ13C and δ15N) in different particle size fractions. Furthermore, Person correlation was used to determine the relationship between SOC and chemical and geo-physical properties of soil under different land use. Finally, discriminant analysis was applied to the data to predict the model of TOC (%) and SOC contents with respect to land use and depth. The results from MANOVA showed that, the conversion of secondary forest to rubber plantation caused significant decline of SOC on top soil (0-30cm). Conversely, converting rubber to oil palm plantation and pasture lead to net gain of SOC. Relative to the soil depth, the top soil 0-30 had greater contents of SOC than sub soil of 30-60 and 60-90 cm. However, in relation to δ13C & δ15N in different land use and depth, the value of δ13C was enriched by increasing the depth of profile. According of different plant species, the value of δ13C at top soil in pasture site indicted that the source of carbon in this site was from pasture δ13C (-19.38), by increasing the depth of profile, the source of carbon was attributed to rubber plantation as revealed by δ13C (-26.67) value. Interestingly, unusual value of δ15N was reported on topsoil 0-30cm, which might be a useful indicator of the source and limited level of nitrogen in the area of study. Regarding to physical fraction, the highest value of SOC, δ13C and δ15N were found in fine particles (clay and silt). Meanwhile, FTIR result revealed that, land use and soil texture plays the significant role for SOC composition. This study concluded that, the relative distribution of SOC, its fractions, carbon δ13C and nitrogen δ15N stable isotopes and FTIR absorbance can be good indicators of the soil organic matter (SOM) quantity and quality. This study therefore recommended that, conversion of rubber to other plantation has more advantage to gain more carbon rather than conversion of secondary forest to plantation, and to quantify the effects of land-use changes and soil texture on soil organic carbon distribution, carbon stored in subsoil and chemical composition of SOM should be taken into account