Construction of a Green and Sustainable Cultivation Model for Annual Forage Oat in Alpine Ecosystems: Optimization and Synergistic Mechanisms of Combined Application of Microbial Fertilizers and Organic Fertilizers

The aim of this study was to establish a green fertilization regime combining microbial fertilizers and livestock manure organic fertilizer for two dominant oat cultivars (<i>Avena sativa</i> L. ‘Baiyan No.7’ and ‘Qingyin No.2’) in alpine ecosystems, providing technical support for sustainable forage production systems in grassland pastoral areas of the Qinghai-Tibet Plateau. The experiment was conducted following the principles of a randomized block design, with five application rates each of effective microbial fertilizer (EM) and compound microbial fertilizer (FH) applied in combination with 18,000 kg·hm⁻² of livestock manure organic fertilizer to systematically analyze their effects on oat agronomic traits, yield quality, and soil health. Key results demonstrated the following: for <i>Avena sativa</i> ‘Baiyan No.7’, effective microbial fertilizer (EM) application at 15.00 kg·hm⁻² significantly increased plant height by 41.29% (<i>p</i> < 0.05), while effective microbial fertilizer (EM) at 18.75 kg·hm⁻² optimized stomatal conductance and the transpiration rate by 73.29% and 46.42%, respectively. For <i>Avena sativa</i> L.‘Qingyin No.2’, compound microbial fertilizer (FH) application at 22.50 kg·hm⁻² enhanced plant height and relative chlorophyll content (SPAD value) of the flag leaf by 50.92% and 47.75%. Yield analysis revealed that compound microbial fertilizer (FH) application at 22.50 kg·hm⁻² increased the fresh forage yield and dry matter yield of ‘Baiyan No.7’ by 34.53% and 38.64%, respectively, with crude protein content reaching 11.02%. Maximum fresh forage yield (38,073.00 kg·hm⁻²) for ‘Qingyin No.2’ was achieved with effective microbial fertilizer (EM) at 11.25 kg·hm⁻², while compound microbial fertilizer (FH) at 22.50 kg·hm⁻² facilitated synergistic accumulation of crude protein (12.57%) and soluble sugars (15.58%). Soil organic carbon increased by 28.85% under compound microbial fertilizer (FH) at 22.50 kg·hm⁻² for ‘Baiyan No.7’, and by 26.21% under effective microbial fertilizer (EM) at 18.75 kg·hm⁻² for ‘Qingyin No.2’. In summary, a cultivar-specific green fertilization system was established: for <i>Avena sativa</i> L. ‘Baiyan No.7’: the application of 18.75 kg·hm⁻² effective microorganisms fertilizer with 18,000 kg·hm⁻² organic manure; for <i>Avena sativa</i> L. ‘Qingyin No.2’: the application of 22.50 kg·hm⁻² compound microbial fertilizer with 18,000 kg·hm⁻² organic manure. This system achieved triple sustainability objectives in alpine oat production: enhancing yield, optimizing quality, and improving soil health.