Impact of heavy rainfall and liquid fertilizers on microbial communities and leachate in compost-amended soil

Climate change is increasing risks to agriculture and soil stability, with soil erosion and flooding being significant global threats that reduce crop yields and degrade soil quality. Tightly correlated with the soil’s response to these changes are the impactful and diverse soil microbiota. As primary drivers of organic matter decomposition, microorganisms convert plant inputs into humus and cell residues. This enhances soil’s physical structure, improves pore formation, and consequently, water-retention and infiltration capacity.To identify and model the effects of agricultural practices, the CARA project [1] is implementing bacterial traits to improve soil resilience under current and future rainfall conditions. This was achieved using a carefully designated rainfall simulator, capable of precisely regulating droplet size and precipitation intensity while maintaining natural terminal velocity, thereby enabling the recreation of various rainfall scenarios. Two scenarios were selected and tested on artificial soil columns with varying content of compost-based organic matter: a current scenario, relating to the precipitation events in Austria, and a future scenario, anticipating increased rainfall intensity and longer dry periods. Furthermore, certain soil columns were supplemented with animal- and plant-based liquid fertilizers to enhance microbial activity.The aim was to assess the influence of microbial activity on soil structure and its capacity for water retention. We identified that the precipitation scenarios exhibited distinct microbiomes across the treatments and over time, with rainfall intensity influencing soil microbial communities by washing out specific taxa, such as Bacilli and Limnochordia, which were subsequently detected within the leachate. Validation experiments in microcosms confirm the observed evaporation reduction and the treatments with liquid fertilizer showed the highest water retention. Our findings offer a basis for evaluating microbiome-based strategies to enhance soil resilience under climate-driven changes in rainfall patterns.[1] Climate change adaptation through flood-reducing agriculture (CARA): https://projekte.ffg.at/projekt/4754252