Abstract
Hybrid maize on acidic Ultisols depends on mineral NPK fertilizer, and its cost limits smallholder returns in Bengkulu, Indonesia. Oil palm empty fruit bunch (EFB) is an abundant local waste that can be fermented into a liquid organic fertilizer (POC). We tested how much of the recommended NPK dose POC can replace without lowering grain yield or nutrient uptake. A randomized complete block field experiment with four replications compared an unfertilized control, 100% NPK (138 kg N, 54 kg P2O5, and 60 kg K2O ha−1), 75%, 50%, and 25% of that dose combined with 3,333 L ha−1 of POC, and POC alone. Full NPK produced 7.92 t ha−1 of grain. Replacing 25% and 50% of the NPK dose gave 8.15 and 7.34 t ha−1, and neither differed from full NPK (Tukey HSD, p < 0.05), whereas replacing 75% reduced yield to 6.01 t ha−1. Nitrogen uptake matched full NPK at 25% replacement and was 13% lower at 50% replacement. Agronomic efficiency of N rose from 30.6 to 37.9 kg grain per kg N at 25% replacement. Apparent N recovery (49.8 to 62.0%) was not separated by Tukey's test. Soil pH after harvest was higher than under full NPK once 50% or more of the NPK dose was replaced. Replacing up to 25% of NPK with fermented EFB liquid fertilizer maintained yield and N uptake on this Ultisol, and 50% replacement kept yield but reduced N uptake. The result comes from one season at one site and lacks a cost analysis.