Integrating critical values of soil drivers for mitigating GHGs: An assessment in a sugarcane cropping system

Agricultural practices can reduce emissions of greenhouse gases (GHG). The definition of management practices toward mitigating GHG emissions could gain accuracy by integrating critical values of soil variables related to GHG fluxes. The aim of this study was to combine critical values of soil variables determining groups of GHG fluxes with similar and/or opposite direction of carbon dioxide (CO₂), nitrous oxide (N₂O) and methane (CH₄). We determined CO₂, N₂O, CH₄ fluxes, soil temperature, gravimetric soil moisture (GSM), soil inorganic nitrogen (SIN), soil bulk density (SBD), soil porosity (P), and water-filled pore space (WFPS) monthly in three consecutive growing seasons in a sugarcane agroecosystem. The regression tree method defined groups of emission. Six terminal groups of CO₂, N₂O fluxes, and four for CH₄ fluxes were determined. The critical values of soil variables that defined the terminal groups with the highest fluxes were soil temperature (>19 °C) and GSM (>35.2%) for CO₂, GSM (>29.2%) and SIN (≤1.1 ppm) for N₂O, and GSM (>24.9 °C), SBD (>0.98 g cm^-3) and SIN (>1.82 ppm) for CH₄. Trade-offs were found among GHGs: N₂O emissions were high and CO₂ emissions were low when GSM and soil temperature ranged from 29 to 35% and 14-19 °C, respectively (moderate values). CO₂ emissions were high and N₂O emissions were the lowest when GSM was equal or lower than 29.2% and soil temperature ranged from 19 to 21.3 °C. In this study, we highlight that management practices aimed to mitigate GHG fluxes should consider the integrated analysis of critical values of soil variables for GHGs together in order to avoid trade-offs.