Fertilization practices are still largely dependent on chemical fertilizers to increase crop productivity; however, their excessive use has been shown to degrade soil quality, suppress soil microorganism activity, and reduce nutrient use efficiency. This challenge is even more apparent in Inceptisol that are poor in organic carbon and phosphorus, resulting in suboptimal sweet corn productivity. Meanwhile, abundant organic waste has not been fully utilized as organic fertilizer, even though it has the potential to improve the physical, chemical, and biological properties. This study aims to increase soil phosphorus availability while reducing dependence on chemical fertilizers by combining compost enriched with Korean Natural Farming liquid organic fertilizer (LOF KNF) with NPK fertilizer at different doses. The study using a single-factor Complete Randomized Block Design (CRBD) with 10 treatments and three replications. Treatments consisted of A0, non-fertilizer control; A1, 100% NPK; A2–A5, decreasing NPK rates (75, 50, 25, and 0%) combined with increasing proportions of market compost and KNF LOF; and A6–A9, decreasing NPK rates (75, 50, 25, and 0%) combined with increasing proportions of mixed compost and KNF LOF. Data were statistically analyzed using ANOVA, DMRT, and Pearson's correlation. The results showed that treatment with compost enriched with LOF KNF and the combination with NPK significantly affected all parameters observed. Combination treatment of 50% mixed compost + 50% NPK + LOF KNF (A7) was the best treatment, increasing soil available P from 8.08 ppm to 15.96 ppm (97.52%), plant tissue P concentration from 0.18% to 0.42% (133.3%), plant height from 121 cm to 163 cm (34.71%), total fresh weight from 402 g to 723.33 g (79.93%), total plant dry weight from 180.67 g to 486.33 g (169.18%), and fresh ear yield from 4.71 kg to 9.2 kg, increasing by 95.32% (15 ton/ha) compared to the unfertilized control. Pearson's correlation analysis revealed strong positive correlations between soil available P and plant P tissue (r = 0.882**), total dry weight (r = 0.700**), and fresh ear yield (r = 0.737**). These findings demonstrate that partial substitution of chemical fertilizers with compost enriched with LOF KNF represents an effective fertilization strategy for improving Inceptisol fertility and enhancing sweet corn productivity.