Effect of Humic Acid-based Bio-stimulant on Soil Fertility Status in Vertisol under Rice Cultivation of Chhattisgarh, India

A field experiment was carried out during the kharif seasons of 2023 and 2024 at the Research Farm of Indira Gandhi Krishi Vishwavidyalaya (IGKV), Raipur, Chhattisgarh, India, to evaluate the influence of a humic acid-based biostimulant on the fertility status of a Vertisol in Chhattisgarh. The experiment was established using a randomised block design (RBD) with twelve treatments, each replicated three times. The treatments comprised T1 – recommended dose of fertilisers (RDF; 120:60:40); T2 – RDF + root dipping in humic acid powder solution (1 g/L); T3 – RDF + humic acid powder at 250 g/acre (soil application, SA); T4 – RDF + humic acid powder at 500 g/acre (SA); T5 – RDF + humic acid powder at 1000 g/acre (SA); T6 – 80% RDF + root dipping in humic acid powder solution (1 g/L); T7 – 80% RDF + humic acid powder at 250 g/acre (SA); T8 – 80% RDF + humic acid powder at 500 g/acre (SA); T9 – 80% RDF + humic acid powder at 1000 g/acre (SA); T10 – 80% RDF + humic acid powder at 1 g/L (foliar spray, FS); T11 – 80% RDF + humic acid powder at 2 g/L (FS); and T12 – 80% RDF + humic acid powder at 4 g/L (FS). The findings indicated that the different combinations of humic acid-based biostimulant applications, administered through soil and foliar methods alongside 80% or 100% RDF, had no statistically significant effect on soil pH, electrical conductivity (EC; dS/m), organic carbon (OC; %), available nitrogen and potassium (kg ha⁻¹), or the concentrations of micronutrients, including zinc, manganese, copper and iron (mg kg⁻¹). In contrast, soil-available phosphorus (kg ha⁻¹) differed significantly among treatments, with the highest concentration observed under RDF + humic acid powder at 500 g/acre (T4), followed by RDF + humic acid powder at 1000 g/acre (T5).