Potassium application enhances vegetative and reproductive yield of Zygopetalum maculatum and reduces post-flowering K depletion from storage organs of the orchid

The orchid cultivation is a significant sector in floriculture industry, and Zygopetalum maculatum is one of the most important orchid species of this industry due to its captivating fragrance and aesthetic appeal. Orchids, being epiphytic, are typically grown in soilless media, which lack essential macronutrients like nitrogen (N), phosphorus (P) and potassium (K), crucial for overall plant growth. Literature cited suggest several studies on combined effect of NPK on orchids, however, the studies on the impact of sole K application on morphological traits, and flower yield of Zygopetalum maculatum orchid have not been cited. Hence, this study was designed to explore the impact of K supplementation on morphological traits, floral yields, K uptake by the flowers, K dynamics in plant parts, and vase life of Zygopetalum maculatum flowers. The experiment was laid out in completely randomized design with six treatments of K application (i.e. T₁ = No K in fertigation solution (K₀), T₂ = 10 mg K per L fertigation solution (K₁₀), T₃ = 25 mg K per L fertigation solution (K₂₅), T₄ = 50 mg K per L fertigation solution (K₅₀), T₅ = 75 mg K per L fertigation solution (K₇₅) and T₆ = 100 mg K per L fertigation solution (K₁₀₀)), each treatment was replicated four times. The plants under the experimentation were treated with the nutrient solution weekly once. Results showed that K application enhanced water-extractable K content and dehydrogenase activity in the potting media. Morphological parameters such as bulb size, leaf number were significantly increased under the K₁₀₀ treatment. Floral yields, including spike length, floret number per spike, floret dimension, and flower biomass, were also substantially higher with K supplementation. The K₁₀₀ treatment produced 167% higher number of flower spike per plant with 44.4% higher number of significantly bigger sized florets per spike over K₀ treatment. K content in leaves, bulbs, and roots significantly increased with K application. Flowering induced K reduction from back bulbs, leaves and roots. The post-flowering K reduction from different plant parts was minimized by K₁₀₀ treatment. Partial regression analysis showed one unit K uptake by flowers caused, ~ 0.227, 0.564 and 0.317 unit K reduction from leaf, back bulb, and roots, respectively. Moreover, flowers from the K₁₀₀ treatment exhibited an extended vase life compared to other treatments. Thus, it can be recommended that, 100 mg K L^-1 fertigation solution should be applied weekly to sustainably improve Zygopetalum maculatum yields.