Volatile organic compound emission and biochemical properties of degraded Ultisols ameliorated by no tillage and liming

The Ultisols in the Raña de Cañamero area in Southwest Spain showed aluminum (Al) phytotoxicity, and the clearance of natural vegetation and decades of intensive conventional agriculture caused the deplation of soil organic matter (SOM). Therefore, we studied the long-term effects of no tillage and liming using sugar beet foam (SF) and red gypsum (RG), alone or in combination, on the restoration of Ultisols affected by acidification, Al phytotoxicity, and SOM depletion. We measured the main soil chemical properties, soil microbial biomass, soil enzyme activities involved in carbon, nitrogen, phosphorus, and sulfur mineralization, and the emission of volatile organic compounds (VOCs). The results indicated that liming effectively neutralized the soil acidity in the long term and, in combination with no tillage, significantly increased soil microbial biomass and enzyme activities. Twenty-three VOCs were detected using the proton transfer reaction-time of flight (PTR-ToF) technique, and both liming and tillage changed the VOC emission patterns. The greatest difference in VOC emission pattern was observed between no-tilled un-amended soils and tilled lime-amended soils, suggesting the activation of different metabolic pathways within the microbial communities of soils under different management. Differences in VOC emission patterns could be attributed to the decomposition of carbohydrates, which were also sustained by the higher enzyme activities in the lime-amended soils.