Miss Nina Hennings1, Miss Katharina M. Fricke1, Prof. Dr. Michaela A. Dippold1, Prof. Dr. Yakov Kuzyakov2

1University Of Göttingen, Göttingen, Germany, 2RUDN University, Moscow, Russia

Indonesia´s rainforests are increasingly threatened by the expansion of agricultural monocultures – mainly oil palm plantations. These conversions to plantations are especially negative for sensitive ecosystems such as riparian areas.

We i) assessed the carbon (C) stocks after conversion of riparian rainforest to oil palm plantations and ii) analyzed how nitrogen (N) fertilization and herbicide application affect biodiversity and soil fertility in oil palm plantations. Activation of microorganisms for soil organic matter (SOM) decomposition leads to increased CO2 emissions and soil C losses. On the other hand, intensive herbicide use may hamper microbial activity and lead to lower CO2 emissions and consequently increased C storage. Field data showed a decrease of C stocks in the topsoil for 4% and 8 % from riparian forests to riparian and well-drained oil palm plantations. Soil from oil palm plantations showed up to two times increased CO2 emissions under higher N fertilization compared to the reduced N fertilization, which is indicative for a strongly nutrient limited ecosystem. N fertilization activated microorganisms and destabilized SOM, leading to more CO2 emitted to the atmosphere. Herbicide application in the weeding circle enhances microbial activity and might provide an additional nutrient source. Therefore, SOM decomposition was intensified with herbicide and fertilizer application. In contrast, SOM was stabilized under lower N fertilization levels without herbicide spraying. Our results from field and laboratory experiments emphasize the risk of deforestation and of management intensification of oil palm plantations reducing SOM stocks and increasing greenhouse gas emissions.

Biography: To be confirmed.

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