Implementation of Good Agricultural Practices (GAP) in Kaempferia galanga L.: Enhancing Inorganic Fertilizer Efficiency through Substitution with Organic Fertilizers and Plant Growth Regulators (PGRs)

Kaempferia galanga L. (kencur) is a high-value medicinal plant widely valued for its bioactive compound, ethyl p-methoxycinnamate (EPMC), yet on-farm productivity remains limited. This study assessed the implementation of Good Agricultural Practices (GAP) through the integration of organic fertilizers, reduced inorganic fertilizers, and plant growth regulators (PGRs; NAA and BA) to enhance rhizome yield, bioactive quality, and soil fertility. A randomized complete block design with nine treatments and three replications was conducted, combining varying doses of NPK fertilizer, cow manure, and PGRs. The treatment combining 300 kg NPK + 10 t ha⁻¹ cow manure + NAA + BA (P4) produced the highest rhizome yield (37.75 t ha⁻¹) with a Relative Agronomic Efficiency of 131.88%. This treatment also achieved the highest simplisia content (21.89%) and EPMC concentration (3.94%), while improving post-harvest soil nutrient availability, particularly nitrogen, phosphorus, and potassium. The integration of organic fertilizers with PGRs enhanced nutrient uptake, optimized photosynthate allocation, and stimulated secondary metabolite accumulation. The results demonstrate that inorganic fertilizer inputs can be reduced by up to 50% without compromising yield, simultaneously improving phytochemical quality and supporting soil sustainability. Overall, the synergistic application of organic and inorganic fertilizers with PGRs provides a practical GAP-based strategy for sustainable cultivation, increasing rhizome productivity, enhancing bioactive compound accumulation, and promoting environmentally responsible agricultural practices. These findings offer actionable guidance for improving the competitiveness of Indonesian herbal products in international markets. Keywords: ethyl p-methoxycinnamate; GAP; Kaempferia galanga L.; plant growth regulators; sustainable agriculture.