SEEDLING VIGOR AND YIELD OF JAPONICA RICE SUPPLEMENTED WITH HUMIC ACID

This study evaluated the effects of different humic acid levels, organic fertilizer, and half the recommended inorganic fertilizer rate on Japonica rice growth and yield. Seedling vigor, influenced by genetic and environmental factors such as nutrient availability and soil conditions, is crucial for plant establishment, stress tolerance, and overall crop productivity. Despite being a semi-aquatic species, rice is sensitive to various stresses that affect growth and yield. A field experiment was conducted in Salvacion, Alicia, Isabela, during the wet season using a randomized complete block design (RCBD) with six treatments and three replications. Seedling growth was assessed 25 days after sowing, and plant growth parameters were measured at 40 days after transplanting. Results showed no significant differences in root length at 20 days after sowing, but at 40 days after transplanting, plants treated with 5 kg ha⁻¹ humic acid had 17.73% longer roots than those receiving the standard inorganic fertilizer rate. Fresh root weight increased with 2.5 and 5 kg ha⁻¹ humic acid, while panicle length improved with 2.5–7.5 kg ha⁻¹. Although filled grain count, filled grain weight, and 1000-grain weight were not significantly affected, Treatment 4 (40-5-30 kg NPK ha⁻¹ + 20 bags organic fertilizer + 7.5 kg humic acid) achieved the highest yield at 3.44 t ha⁻¹, a 21.49% increase over the control. These findings suggest that integrating humic acid with organic and reduced inorganic fertilizers enhances Japonica rice yield while promoting sustainable farming.