Effect of Nitrogen Concentration on Plant Growth and Yield of Black Ginger Cultivated in Soilless Culture System

This study investigated the influence of nitrogen concentration on the growth, yield, and phytochemical profile of black ginger (Kaempferia parviflora) cultivated in a soilless culture system. Black ginger, widely recognized for its medicinal properties and high domestic demand, faces production challenges that limit its supply. To address this, the experiment employed a completely randomized block design using 8‐month-old rhizomes subjected to five nitrogen treatments (50, 100, 150, 250, and 300 ppm) while maintaining constant phosphorus and potassium levels. Morphological parameters such as plant height, vegetative fresh weight, number of tillers, SPAD value, fresh rhizome yield, and the rhizome-to-shoot ratio were measured to assess growth performance. Although plant height was statistically similar across treatments, both vegetative fresh weight and fresh rhizome yield increased with higher nitrogen levels, peaking at 250 ppm before declining at 300 ppm. The optimal rhizome-to-shoot ratio was also achieved at this intermediate concentration, indicating effective biomass partitioning toward the valuable storage organs. Phytochemical analyses were conducted to quantify total phenolic content (TPC), total flavonoid content (TFC) and the concentration of 4,5,7‐trimethoxyflavone, a key methoxyflavone linked to various therapeutic activities. Interestingly, while the highest TPC and TFC were observed at 50 ppm nitrogen, the level of 4,5,7‐trimethoxyflavone was maximized at 250 ppm. Antioxidant activities measured via DPPH radical scavenging and FRAP assays supported these findings, suggesting that both low and moderate-high nitrogen supplies benefit the plant’s secondary metabolism. Overall, the study demonstrates that optimizing nitrogen fertilization in a soilless culture system can significantly enhance both the yield and medicinal quality of black ginger.