Assessment of the agronomic impact of rice husk ash, volcanic ash, green compost and wood biochar as soil amendments

Today's agriculture faces the challenge of guarantee food supply of a growing population while human activity has already degraded nearly 40 % of the world's soils [1], which lose productive capacity and increase dependence on mineral fertilizers. In this context, the valorization and recycling of mineral and agricultural waste for use as substrates or soil amendments promotes the local and sustainable economy as well as the implementation of activities based on closing the soil nutrients’ cycle. Moreover, pyroclastic rocks and volcanic ashes formed by volcanic eruptions are usually rich in Si, Ca, Mg, Al, Fe, K, P and S [2], so they can be used in agriculture as inorganic mulch. Looking for an effective solution to the great waste generation and the current challenges of sustainable agriculture [3], this study addresses the agronomic effects of the application of contrasting inorganic and organic materials including green compost, wood biochar, rice husk ash and volcanic ash released in the recent eruption of the Tajogaite volcano (La Palma Island, Spain) as amendments of an alkaline soil typical of the Mediterranean basin. For this purpose, barley seeds were planted and grown under controlled conditions in a greenhouse for 60 days on a Luvisol amended with the above-mentioned materials.The organic amendments improved soil physical properties, such as the reduction of bulk density and of the soil resistance to penetration, and increased the organic carbon content. Biochar increased the amount of refractory organic matter of the Luvisol. The application of rice husk ash, volcanic ash, and to a lesser extent the green compost, increased the nutrient content of the soil. Nevertheless, no significant differences were observed on germination rates, productivity and abiotic markers of stress of the barley plants.Acknowledgements: Authors thank the financial support from the Spanish Ministry of Science and Innovation (MCIN) under the projects RES2SOIL (PID2021-126349OB-C22) and TUBOLAN (PID2019-108672RJ-I00) supported by MCIN and AEI. The European Joint programme EJP SOIL funded from the EU Horizon 2020 research and innovation programme (Grant agreement Nº 862695) is also thanked for funding the subproject EOM4SOIL.References:[1] Gibbs, H.K., Salmon, J.M., 2015. Appl. Geogr. 57: 12-21.[2] Ramos, C.G., Querol, X., Dalmora, A.C., Pires, K.C.J., Schneider, A.H., Oliveira, L.F.S., Kautzmann, R.M., 2017. J. Clean. Prod., 142: 2700-2706.[3] De la Rosa, J.M., Campos, P., Diaz-Espejo, A., 2022. Agronomy, 12: 2321. https://doi.org/10.3390/agronomy1210232