Legacy effects of 41 years of tillage and fertilization on biological nitrogen fixation and nutritional status of hairy vetch in a continuous cotton system

Abstract

Legume cover crops (CCs) rely on a dynamic contribution of soil-derived nitrogen (N) and biological nitrogen fixation (BNF) to maintain optimum N status, yet how long-term agronomic management shapes this relative contribution remains poorly understood. This study leveraged a 41-year continuous cotton (Gossypium hirsutum L.) system to evaluate how legacy effects of tillage and N fertilization influence BNF, legume N nutritional status, and N sources in hairy vetch (Vicia villosa). Using the ¹⁵N natural abundance method and multivariate analyses, we found that tillage was the dominant factor affecting N dynamics: no-till (NT) plots exhibited higher N status, soil organic matter, soil-derived N, and total N uptake than conventional tillage. Fertilization effects were less pronounced but modulated BNF efficiency. However, NT alone was insufficient to overcome N limitation under unfertilized conditions, as indicated by similarly low nitrogen nutrition index values and overlapping distributions in both CT-0N and NT-0N treatments, highlighting the need for integrated management. These findings underscore how legacy effects of long-term practices shape N acquisition by legumes and support combining NT with crop rotation-specific N fertilization to optimize N inputs and sustain CC performance in low-input systems.

Core Ideas

• Hairy vetch grown under conventional tillage was more limited by N than no-till, with differences widening at higher N fertilization rates.
• Atmospheric N contribution was higher under conventional tillage than no-till, with greater differences at higher fertilization rates.
• No-till was associated with higher soil organic matter and soil N uptake, supporting improved legume N status.
• No-till alone was insufficient to prevent N limitation in hairy vetch under unfertilized conditions.