Global direct nitrous oxide emissions from the bioenergy crop sugarcane (Saccharum spp. inter-specific hybrids)

Sugarcane is the second largest bioenergy crop in the world and it accounts for 80% of global sugar production. Grown mostly in wet and warm tropics with relatively high nitrogen (N) fertiliser input and crop residue retention, sugarcane production is a significant source of nitrous oxide (N₂O) emission. Yet, a global evaluation of research on N₂O emission from sugarcane crop is lacking. Here, we conducted a meta-analysis using data from 141 measurements compiled from 15 sugarcane field studies reported from different countries to i) quantify N₂O emissions and emission factors (EFs) globally, and for tropics and sub-tropics, and ii) identify the key factors that promote N₂O emission. Our analysis shows that the global mean total N₂O emission from sugarcane production reached 2.26 (CI: 1.93-2.62) kg N₂O-N ha^-1 yr^-1 with an estimated EF of 1.21% (CI: 0.971-1.46%). N₂O emissions increased exponentially with increase in N fertiliser rate, questioning the adequacy of Intergovernmental Panel on Climate Change (IPCC) default EF value (1%) for sugarcane N₂O emission estimation. Mean total N₂O emissions and EFs in tropics and sub-tropics did not vary significantly. Supplementing synthetic N fertiliser (SN) with organic amendments (OA) significantly increased mean N₂O emission (~1.4-fold) and EF (~2.5-fold) compared to SN. A remarkable reduction in N₂O emission (38.6%) and EF (61.5%) was evident when enhanced efficiency fertilisers (EEF) replaced SN. In contrast, crop residue removal had little impact on N₂O emission and EF, but both parameters showed an upward trend with irrigation and increased rainfall. Soil carbon content and pH were emerged as key regulators of sugarcane N₂O emission and EF. It is concluded that global sugarcane N₂O emission could be significant and that there is considerable prospect for mitigating the emission through innovative nutrient formulations and precision agriculture that help meet crop nutrient demand without compromising environmental imperatives.