Regrowth and Yield Formation of ‘Qingtian No. 1’ Oat in Response to Cutting Management

The optimization of mowing management is crucial for establishing a high-yielding “one sowing, two harvests” system for oat (Avena sativa L.) forage production in the alpine regions of the Tibetan Plateau. This study aimed to identify the optimal combination of cutting stage and stubble height to maximize the total seasonal productivity of the system. A two-factor field experiment, arranged in a randomized complete block design, was conducted over two consecutive growing seasons (2024 and 2025) using the local cultivar ‘Qingtian No. 1’. The treatments consisted of two cutting stages (flowering stage, C1; milk stage, C2) and three stubble heights (5 cm, H1; 10 cm, H2; 15 cm, H3). Regarding regrowth phase performance, mowing at the flowering stage (C1) resulted in significantly superior agronomic traits (e.g., stem diameter, tiller number) and photosynthetic characteristics compared to the milk stage (C2). In terms of forage quality, the C2H2 treatment maximized water-soluble carbohydrate content but also led to elevated fiber levels. However, the key metric for system evaluation—the total seasonal dry matter yield—was predominantly governed by the cutting stage. Mowing at the milk stage (C2) consistently resulted in a higher total yield than C1, with optimal combinations yielding 1.31 t/ha (C2H1) in 2024 and 1.25 t/ha (C2H2) in 2025. This advantage was primarily due to a substantially greater first-harvest yield under C2, which outweighed the regrowth benefits of C1. A comprehensive evaluation based on total system productivity and forage quality indicates that mowing at the milk stage (C2) is the optimal strategy for achieving high total output. For ‘Qingtian No. 1’ oat in this region, a stubble height of 10 cm (as in the C2H2 treatment) is recommended to ensure robustness across years. This management strategy secures a high total seasonal forage yield through effective biomass allocation between harvests, extending the supply window and offering a sustainable cultivation model for this ecologically vulnerable region.