Humic Acid-Driven Soil Stability and Nutrient Absorption: Comparing Organic and Synthetic Fertilization in Maize Production

Soil organic matter (SOM) plays a pivotal role in enhancing soil's physical and biological properties, contributing to improved crop productivity and long-term agricultural sustainability. Among the components of SOM, humic acid (HA) is particularly important due to its capacity to enhance soil structure and promote nutrient availability. While previous studies have primarily focused on the impact of naturally derived HA on soil properties, this study investigates the effects of HA on soil aggregation and stability under different fertilizer regimes. The experiment was conducted during the summer cropping season with maize (Zea mays L.) grown under both organic and synthetic fertilizer treatments. The organic fertilizer treatment involved the incorporation of barley (Hordeum vulgare L.) and hairy vetch (Vicia villosa R.) residues five days prior to maize cultivation, whereas the synthetic fertilizer treatment applied recommended rates of NPK fertilizers in accordance with Korean agricultural guidelines. Results showed that the organic fertilizer treatment significantly improved soil aggregation and stability, as indicated by the mean weight diameter (MWD) of soil aggregates (p < 0.05), compared to the synthetic fertilizer treatment. This enhancement was largely attributed to the increased quantity and quality of HA derived from organic inputs. The organic treatment yielded nearly double the amount of HA compared to the synthetic treatment. Additionally, the organic treatment demonstrated a 140% increase in MWD and a 40% higher total phenolic content than the synthetic counterpart. Furthermore, maize cultivated under organic treatments exhibited significantly higher macronutrient absorption (p < 0.001), an 11% increase in above-ground biomass, and a 21% increase in grain yield compared to synthetic fertilizer treatments. These findings suggest that the incorporation of fresh organic residues can effectively enhance HA characteristics in soil, thereby improving soil structure and promoting sustainable crop productivity.