Ash-affected yet resilient: soil degradation and recovery in banana agroecosystems after the 2021 Tajogaite eruption

Soil degradation in semi-arid island agriculture is driven by the combined pressures of land scarcity, intensive management and increasing climate variability. In volcanic environments, explosive eruptions add a further layer of disturbance, through abrupt ash deposition that can alter soil salinity, structure and organic matter dynamics. The 2021 Tajogaite eruption (La Palma, Canary Islands, Spain) covered large areas of irrigated banana (Musa spp.) plantations with centimetre-thick ash layers, raising concerns about long-term soil degradation, loss of productivity and the sustainability of these agroecosystems. Yet, medium-term trajectories of soil degradation and recovery after such events remain poorly documented.
We evaluated soil health trajectories in banana plantations affected by Tajogaite ash, comparing conditions 6 and 32 months after the onset of the eruption. Topsoil (0–20 cm) was sampled in eight commercial farms located along the eastern (n = 5) and western (n = 3) flanks of the new cone, spanning altitudinal and distance-to-sea gradients. At each farm (1–3 composite samples per site and date) we measured pH, electrical conductivity (EC, 1:5), oxidizable organic carbon, total nitrogen, loss on ignition, available P, exchangeable cations (Ca, Mg, K, Na and selected micronutrients), texture, water-stable aggregates (WSA), water holding capacity (WHC), basal and glucose-induced respiration, and the microbial metabolic quotient (qCO₂). Site-specific rainfall and ash-layer thickness were compiled, and texture- plus organic-matter-based pedotransfer functions were used to obtain first-order estimates of field capacity and permanent wilting point, for comparative purposes only.
Preliminary results reveal heterogeneous but generally resilient soil responses to ash deposition. In heavily ash-loaded western farms, EC and exchangeable Na declined from initially moderate–high values to clearly lower levels 32 months after the eruption, indicating a partial alleviation of salinisation risk. In eastern farms, EC remained within a moderate range, sometimes increasing slightly in line with resumed fertilisation, but without evidence of secondary salinisation. Across most sites, soil organic matter and total N were maintained or slightly increased, while WSA and WHC were stable or improved, suggesting a consolidation of soil structure as ash was progressively incorporated into the plough layer. Basal and induced respiration and qCO₂ values at both sampling times indicate active and reasonably efficient microbial communities, with no signs of persistent biological degradation.
Overall, banana plantation soils on La Palma show substantial functional resilience to volcanic ash inputs when supported by irrigation and ongoing management. However, differences between flanks and altitudinal zones point to uneven recovery and highlight specific hotspots of degradation risk. These findings underline the need to integrate hydrological, structural and biological indicators into post-eruption soil monitoring, and provide an empirical basis for designing targeted soil and water management practices that enhance soil conservation and resilience in volcanic island agroecosystems under global change.