Key unknowns in nitrogen budget for oil palm plantations. A review

Nitrogen (N) losses in agroecosystems are a major environmental and economic issue. This issue is particularly pronounced in oil palm cultivation because oil palm production area is expected to increase to 12 Mha by 2050. N fertilization in oil palm plantations is mainly provided by mineral fertilizers, palm oil mill by-products, and biological fixation using legume cover crops. N loss has a major environmental impact during cultivation. For instance, 48.7 % of the greenhouse gases emitted to produce 1 t of palm oil fruit are due to N fertilization. Actually, there is little comprehensive knowledge on how to calculate N budgets in oil palm plantation in order to optimize fertilization, taking into account N leaching and N gases emissions. Here we modeled knowledge about all N fluxes in an oil palm field following standard management practices of industrial plantations, on a mineral soil, from planting to felling after a 25-year-growth cycle. The largest fluxes are internal fluxes, such as oil palm uptake, with 40–380 kg N ha−1 year−1, and the decomposition of felled palms at the end of the cycle, with 465–642 kg N ha−1. The largest losses are emissions of NH3 and leaching of NO3−, corresponding to 0.1–42 % and 1–34 % of mineral N applied, respectively. The most uncertain and least documented fluxes are N losses such as N2O, NOx, N2 emissions, leaching, NH3 volatilization, and runoff. The most critical conditions for N losses occur during the immature phase when young palms uptake is low and during the mature phase in areas with sparse soil cover or receiving high amounts of fertilizers. Data is lacking about the effects of management practices on NO3− leaching and N2O/NOx emissions in those critical conditions.