Soil carbon balance following conversion of grassland to oil palm

Abstract

Oil palm (Elaeis guineensis Jacq.) crops are expanding rapidly in the tropics, with implications for the global carbon cycle. Little is currently known about soil organic carbon (SOC) dynamics following conversion to oil palm and virtually nothing for conversion of grassland. We measured changes in SOC stocks following conversion of tropical grassland to oil palm plantations in Papua New Guinea using a chronosequence of plantations planted over a 25-year period. We further used carbon isotopes to quantify the loss of grassland-derived and gain in oil palm-derived SOC over this period. The grassland and oil palm soils had average SOC stocks of 10.7 and 12.0 kg m À2, respectively, across all the study sites, to a depth of 1.5 m. In the 0-0.05 m depth interval, 0.79 kg m À2 of SOC was gained from oil palm inputs over 25 years and approximately the same amount of the original grass-derived SOC was lost. For the whole soil profile (0-1.5 m), 3.4 kg m À2 of SOC was gained from oil palm inputs with no significant losses of grass-derived SOC. The grass-derived SOC stocks were more resistant to decrease than SOC reported in other studies. Black carbon produced in grassfires could partially but not fully account for the persistence of the original SOC stocks. Oil palm-derived SOC accumulated more slowly where soil nitrogen contents where high. Forest soils in the same region had smaller carbon stocks than the grasslands. In the majority of cases, conversion of grassland to oil palm plantations in this region resulted in net sequestration of soil organic carbon.

Changes in soil organic carbon stocks after conversion from forest to oil palm plantations in Malaysian Borneo

“…Studies of the effects of conversion of forests to oil palm plantations are not only sparse, but also contradictory. Accordingly, some studies have reported a soil organic carbon (SOC) stock decrease (Sommer et al 2000, Hergoualc'h and Verchot 2011, Bruun et al 2013, Chiti et al 2014 or increase (Frazao et al 2013, Goodrick et al 2015 or no change (Tanaka et al 2009, Khasanah et al 2015 following land use conversion to oil palm. These studies mostly focus on the effects of conversion of primary forests to smallscale oil palm plantations, but not to large-scale oil palm plantations that may differ in organic matter management and replantation technique and are, moreover, often the point of the debate regarding deforestation and environmental degradation in tropical areas.…”

Land use conversion in humid tropics influences soil carbon stocks and forms

“…The grasslands showed the highest total soil organic C stock compared to the other land use systems due to the greater ability of grasslands to produce diverse aboveground biomass (Pinheiro et al, 2010) or due to the addition of recalcitrant black C during burning operations (Goodrick et al, 2015). Natural and restored grasslands are effective vegetation types for SOC sequestration due to the higher carbon input from the roots (Wei et al, 2012).…”

“…Soil C exists primarily in three chemical forms, although few attempts have been made to fractionate C based on its faunal oxidation potential or the ecosystem services it renders (Grandy and Robertson, 2007;Berreto et al, 2011). The chemical components of soil C are primarily elemental C (e.g., charcoal, graphite and soot) from geological or biomass burning sources, inorganic C that is derived from geologic or soil mineral sources, such as carbonates (e.g., calcite and dolomite), and organic C from the natural decomposition of plants and animals (Goodrick et al, 2015). Several methods are available for assessing soil C stocks; dry combustion analyzers are the most widely used.…”

Evolution of soil organic carbon during a chronosequence of transformation from cacao (Theobroma cacao l.) plantation to grassland

“…Alternatively, Huang et al (2010), mentioned that over the years, grasslands lose their vocation to accumulate SOC due to a decrease in the system productivity, mainly due to an increasing degradation of its properties, motivated by cattle overgrazing and the type of grassland established. Accordingly to Goodrick et al (2015), some tropical agroforestry systems slowly reduce the SOC content due to the higher N contents that legumes procure (which speeds up the mineralization processes). In addition, a higher STN concentration and higher mineralization, reduces the C/N ratio, resulting in a greater SOM decomposition.…”