Converting already-degraded pasture to oil palm plantations avoids the large loss of stored carbon associated with clearing rainforests to make way for these plantations, according to a long-term, Colombia-based study. The study, which shows that the pasture-based approach is close to carbon neutral in Colombia, provides the first field-based evidence of the effects of oil palm plantations on soil carbon content for a period that extends more than 50 years. Rainforests, particularly in Asia, are a major source of land for newly established plantations that produce palm oil, a vegetable oil with a host of desirable properties found in everything from soap to lipstick to peanut butter. In Sumatra, clearing rainforests to grow oil palms depletes 173 tonnes of carbon per hectare of soil, for example. Researchers are on the hunt for eco-friendly palm oil production alternatives, which don't involve deforestation. Among these, use of pasture land is of great interest but studies evaluating this approach have focused on the soil impacts over time periods of 30 years or fewer, which might be too short to reveal long-term soil changes. To assess whether growing oil palms on pasture can mitigate the loss of carbon from the ecosystem seen in rainforest-based approaches, Juan Carlos Quezada Rivera et al. studied six plots of land where oil palms had grown between 12 and 56 years in the piedmont of the Llanos region in Colombia's eastern plains. (In Colombia, the expansion of oil palm plantations has occurred mainly on pastures in recent decades.) They measured long-term changes in carbon stocks and soil chemical properties to a depth of 50 centimeters, finding that 39% of the original soil organic carbon was lost during the first oil palm rotation cycle. However, the carbon was later redistributed within the soil, with recovery of soil organic carbon in the topsoil compensating for a loss at greater depths.
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