The impact of alfalfa intercropping and conventional tillage on N-cycling microbes: A Tuscan vineyard case study

Vineyards, like other agroecosystems, face great challenges in preventing soil fertility decline and achieving sustainability goals. Addressing soil erosion, the loss of organic matter and nutrient deficiencies are therefore the focal points for future agricultural development. In this study, we evaluated the long-term effects of conventional soil management versus the interrow cultivation of alfalfa on soil physico-chemical properties and on the abundance of key microbial groups involved in the nitrogen (N) cycle along a Tuscan vineyard slope. Under alfalfa covers, qPCR data revealed a significant (p < 0.05) decrease in soil nitrifying and denitrifying bacterial populations carrying the amoA-AOB and nosZ genes, respectively; however, interactions with the hill position were also relevant. Quantitative, functional gene-based predictions showed that alfalfa intercropping induced a higher N₂O production (increment of 142.38 % and 107.47 % at the top and bottom of vineyard, respectively), and a lower N₂O reduction across the vineyard slope (63.42 % at the top and 63.48 % at the bottom) compared to the conventional tillage, influenced by the vineyard slope. The abundance of N-transforming microbial guilds correlated with soil texture and chemical features, such as total organic carbon (TOC), TN and particle size fractions, varying based on management type and slope position. Integrated strategies are needed for ensuring the long-term soil resilience and nutrient balance in Mediterranean viticultural systems.