Quantification of the biogeophysical impact of crop residue management in Europe

Managing jointly the biogeochemical and biogeophysical (e.g. albedo and energy fluxes) impacts of agriculture is essential towards reaching climate-neutral agriculture. Only few observations collected in a small number of sites are available to quantify the impacts of agriculture on both the biogeochemical and biogeophysical effects on climate. The coupling of dedicated crop models with land surface models allows the combined quantification of those effects, but often lacks crop-specific parameterization and accounting of cropland management effects on biogeophysical effects. For these reasons, the biogeophysical and net climatic impact of agriculture on climate remains uncertain.  

Here, we refined spatiotemporal bare soil albedo dynamics and the quantification of crop pigmentation and canopy structure effects on cropland albedo in the ORCHIDEE-CROP land surface model. This model develops a detailed crop growing module based on the process-based STICS formalism.  We further introduced a new module assessing the effects of crop residues on soil albedo and soil evaporation. The model was parameterized and evaluated at nine European cropland flux sites for which detailed management information, field photos, soil moisture and surface albedo monitoring data were available. In addition, we produced a novel daily bare soil albedo product derived from Sentinel-2 at 300 m spatial resolution for Europe. 

Using the refined model we quantified the effect of the presence of crop residues on radiative forcing, soil temperature and soil moisture of winter wheat crops. Simulations with the presence of crop residues left on the soil after harvest in 2-3 months increased surface albedo by approximately 0.08±0.03 in average, with significant spatiotemporal variability influenced by meteorological and soil conditions, as well as tillage practices among sites. We further found that over the same period residue cooled the surface soil by −1.18 ± 1.98 ℃ and enhanced the total soil water content by 35.77 ± 36.23 kg/m2. In a simulation of 10-year dry scenarios, we found that returning crop residues to the field can progressively increase plant available water over multiple years, with the extent of this increase influenced by climatic conditions. This study underscores the significance of the biogeophysical impacts of residue management on surface energy balance and highlights its potential in mitigating climate change, in particular in a warmer drier climate in Europe. The new framework developed in this study allows for a more rigorous assessment of the combined biogeochemical and biophysical impacts of field operations in Earth System Models such as cover crops that could allow climate cooling both through soil organic carbon sequestration and increase in surface albedo.