Effect of increasing nitrogen fertilization on soil nitrous oxide emissions and nitrate leaching in a young date palm (Phoenix dactylifera L., cv. Medjool) orchard

The date palm (Phoenix dactylifera), an important agricultural crop in arid and semi-arid areas around the Mediterranean Sea, has high nutritional, cultural, and economic values. Date palm cultivation in Israel is practiced in the arid and hyper-arid Jordan and Arava Valleys and is associated with high water and nitrogen (N) fertilization inputs, with rates of up to ~170 m³ water and ~6 kg N per full-grown tree annually, on average. While the palm's water needs and budget have been intensively studied, the fate of applied N has received little attention to date. Understanding this fate is especially important since high fertilization rates of ~740 kg N ha⁻¹ may have deleterious effects on the environment. Specifically, soil emissions of nitrous oxide (N₂O) and leaching of nitrate (NO₃^-) are of major concern, due to their impact on climate change and groundwater contamination. We have measured the effect of four levels of N fertigation (fertilization + irrigation), between 0 and 2.55 kg N tree⁻¹ yr⁻¹, on N₂O and NO₃^- fluxes during an annual growth season in a three-year-old date palm orchard located in Israel's hyper-arid Arava Valley. We used static chambers for soil N₂O flux estimations and measured drainage water NO₃^- concentrations at a 60-cm depth, together with a Cl^- mass-balance-based water budget to estimate the NO₃^- leaching. We observed trivial soil N₂O emissions of up to ~0.02% of applied N, while NO₃^- leaching was estimated to be as high as 36%. Dry areas between the trees, which did not receive any fertilization or irrigation, exhibited even lower N₂O emissions than the irrigated areas. Inorganic N, however, accumulated during the dry months in the upper layer of the soil and was later lost at the onset of the winter rains. Our results provide the first-ever estimations of the potential environmental impact of date palm plantations in Israel and the Mediterranean Sea Basin.