Effects of the Mount Marapi Eruption on Plant Diversity and Mineral Status of Soil and Forage in West Sumatra, Indonesia

The December 2023 eruption of Mount Marapi in West Sumatra deposited volcanic ash and gravel across agricultural landscapes, disrupting crop production, forage availability, and livestock health. This study evaluated the effects of the eruption on forage diversity, biomass production, and the mineral status of soils and forages. A survey of 55 cattle farmers across five subdistricts (Ampek Angkek, Canduang, Sungai Pua, X Koto, and Batipuah) classified impacts as severe, moderate, or low. In severely affected zones, farmers reported livestock health problems, and forage biomass declined due to ash deposition. In moderately affected zones, cattle remained healthy; however, the forage supply decreased significantly due to ash contamination and scarcity. In low-impact zones, livestock and forage supply were largely unaffected, though farmers experienced economic losses due to reduced crop yields and lower market prices. Across all zones, 70 forage species were identified, dominated by Pennisetum purpureum (19.2%), Axonopus compressus (14.6%), Digitaria sanguinalis (7.4%), and Cynodon dactylon (5.3%). Forage diversity increased post-eruption, while average biomass (8.9-9.2 tons DM/ha) and carrying capacity (2.2-2.3 AU/ha) did not differ significantly among impact zones (p > 0.05). Most soil and forage minerals, including phosphorus (0.32–0.36%), magnesium (1,321-1,625 ppm), and sulfur (238-257 ppm), remained above deficiency thresholds. However, copper concentrations in forage were consistently low (4.8-5.3 ppm), which is well below the critical requirement of 8 ppm, posing a long-term risk to grazing cattle. These findings demonstrate the resilience of dominant tropical grasses to volcanic ash deposition, suggesting that while forage productivity and mineral availability were largely sustained, persistent copper deficiency requires targeted supplementation strategies to safeguard livestock health and productivity in volcanic regions.