Effects of Professional NPK Fertilizer and Humic Acid on Purple Eggplant during the Second Production Period

Purple eggplant (Solanum melongena L.) has the potential to produce continuously beyond the first harvest, but its productivity may decline during subsequent production periods due to reduced nutrient availability and declining plant vigor. This study aimed to evaluate the effects of professional NPK 16-16-16 fertilizer and humic acid on the growth and yield of purple eggplant during the second production period and to identify the most favorable treatment combination. The study was conducted using a factorial experimental approach involving three NPK fertilizer rates (200, 300, and 400 kg ha?¹) and three humic acid concentrations (2, 4, and 6 g L?¹). The observed parameters included plant height, number of leaves, fruit length, number of fruits per plant, and fruit weight. The results showed that purple eggplant responded differently across the evaluated growth and yield parameters. Humic acid at 4 g L?¹ produced the highest average number of leaves (78.33 leaves plant?¹), while the 6 g L?¹ treatment resulted in the greatest average fruit length (14.17 cm). Increasing the NPK rate from 200 to 400 kg ha?¹ tended to increase the number of leaves, with the highest average recorded at 80.44 leaves plant?¹. Among the treatment combinations, 4 g L?¹ humic acid combined with 400 kg ha?¹ NPK (H2P3) produced the highest number of fruits (17.33 fruits plant?¹) and the highest average fruit weight (129.43 g fruit?¹). These findings indicate that the integration of NPK fertilizer and humic acid has potential for maintaining the growth and productivity of purple eggplant during the second production period, with H2P3 showing the most favorable numerical response among the evaluated combinations. Contribution to Sustainable Development Goals (SDGs):SDG 2: Zero HungerSDG 12: Responsible Consumption and ProductionSDG 15: Life on Land