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Modelling the nitrogen balance of tropical perennial crops: state of the art and challenges for oil palm plantations

Pardon L., Bessou C., Nelson P.N., Caliman J.P.. 2015. In : Environmental protection in a multi-stressed world: challenges for science, industry and regulators. Abstract book. Bruxelles : SETAC Europe, p. 399-400. (Abstracts book (SETAC Europe Annual Meeting), 25). SETAC Europe Annual Meeting. 25, 2015-05-03/2015-05-07, Barcelone (Espagne).

While a number of models exist to estimate nitrogen (N) losses from agricultural fields, they mostly pertain to temperate climate conditions and annual crops. Few models are available for tropical crops [1], [2], and even fewer for perennial crops [3], [4]. The lack of robust N-flux inventories is particularly critical for LCA of perennial and tropical crops. Oil palm is the most rapidly expanding tropical perennial crop, which raises environmental concerns. Beside land-use change and peatland, oil palm agricultural production impacts the environment mainly through the use of synthetic fertilisers, notably nitrogen [5], [6]. The latter is associated with pollution risks of ground and surface water, and emissions of greenhouse gases. Accurate estimation of N losses is critical to assess the environmental impacts of palm plantations. In this study, we reviewed currently-available models for oil palm cultivation, and appraised their capacity to assess the N balances of oil palm agro-ecosystems. We identified various operational and process-based models that could be applied to oil palm, although most of them were not specifically adapted for tropical perennial crops. To our knowledge, APSIM is the only available process-based model of oil palm cultivation that includes N losses [7], but the accuracy of its N loss estimates was untested. Other means of assessment were based on statistical models [8]¿[10] or other approaches [11]¿[13]. Nitrogen balance assessments have shown important uncertainties (Figure). Estimates of N20 and NO3 - rely on very uncertain and sensitive parameters, such as the clay content for instance with the SQCB-NO3 model [13]. These uncertainties are due to a lack of understanding of processes. In particular, it is difficult to study and understand N dynamics over the whole lifespan of oil palm crops (20-25 years) and to account for varying agricultural practices. Adequate data to characterise various cropping systems is often lacking. Further research is required to develop a procedure that provides a robust assessment of the environmental impact of N management in oil palm cultivation. Particularly, this procedure should have the capacity to account for a range of soils, climates, and management practices over the whole cycle. One track to be pursued is the development of an agro-ecological indicator based on Indigo concept [14], [15]. Such an indicator could help to reduce uncertainties in LCA of tropical perennial crops. (Résumé d'auteur)

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