Modelling the long-term impacts of conservation agriculture on soil structure , soil organic matter and the water balance under climate change.

Conservation agriculture practices, such as reduced tillage and residue retention, have gained attention for their potential to enhance agricultural system resilience to climate change and to combat soil degradation. However, conventional soil-crop models usually neglect the dynamics of soil properties, limiting their ability to predict changes in soil quality on the longer time-scales relevant for sustainable soil management. One exception to this is the recently developed Uppsala model of Soil Structure and Function (USSF), which accounts for soil structure dynamics due to both physical (e.g. swell-shrink, sealing, tillage/consolidation) and biological (e.g. root growth, macro-faunal activity, soil aggregation) processes driven by changes in climate or land management. We further developed and applied the USSF model to assess the long-term impacts of conservation agriculture on soil organic matter (SOM) stocks, soil structure, water balance and crop yields.

The model was first calibrated for a winter wheat crop in Zürich, Switzerland, and then used to simulate a baseline period (1985-2015) as well as 18 future climate scenarios for the period 2020 to 2090. Simulations of two contrasting soil management systems were compared: conventional intensive tillage with residue incorporation (CIT) and no-till practices with surface residue retention (CNT), representing a conservation agriculture scenario.

Under current climate conditions, the CNT treatment was able to conserve soil moisture by reducing surface runoff and evaporation, as compared with CIT. However, yields remained similar, as under the wet site conditions, crop growth was not limited by water availability. After 30 years, SOM stocks were slightly higher under CIT, as larger amounts of above-ground biomass were incorporated through tillage compared with incorporation only by bioturbation in the case of CNT. In the future climate projections, grain yields remained stable or increased slightly under warmer site conditions . The development of SOM stocks was strongly dependent on future soil temperatures . However, after 70 years, stocks were on average ca. 14% higher under the CNT treatment compared with CIT.

Although yields did not differ between the two treatments, the USSF model projections showed increased SOM stocks and improved soil structure with no-till and surface residue retention compared with conventional practices. This suggests that conservation agriculture could be a promising strategy for sustaining soil quality and functions in the face of climate change.