Response of Soybean to Different Category of Biostimulants Across Contrasting Himalayan Hill Agro-Climatic Zones

Biostimulants have been extensively studied in horticultural and high-value crops, particularly in developed countries. However, their application in low-value broad-acre crops under diverse hill agro-ecosystems investigations are limited, especially in developing countries dominated by smallholder farming systems. This study evaluated three biostimulant formulations—seaweed extract + vitamin, seaweed extract + humic and fulvic acids, and protein hydrolysate + humic acids—in soybean across three western Himalayan hill agro-climatic zones: Zone I (Akrot; sub-montane low-hill subtropical), Zone II (Palampur; mid-hill sub-humid), and Zone III (Awarna; high-hill temperate wet). Field experiments were conducted in a randomized block design with ten treatments and three replications. Growth and yield parameters were analysed through individual and pooled ANOVA, while treatment responses across environments were assessed using location × treatment interactions. Significant effects of both location and treatment (p < 0.01) were observed for all measured traits. Palampur was the most favourable environment, followed by Akrot, whereas Awarna imposed relatively constrained conditions. Among treatments, T6 showed the most consistent performance and recorded a 48.5% yield advantage over the control, while T9 and T3 performed statistically at par. The findings demonstrate the potential of biostimulants to enhance soybean productivity across diverse Himalayan hill agro-ecosystems.