Effect of Different Levels of Lignitic Coal Derived Humic Acid on Growth of Maize Plants

In view of the high cost of chemical fertilizers, use of natural fertilizer sources for increasing crop production on a sustainable basis has become imperative. A pot experiment was conducted in silty clay loam, mixed, hyperthermic typic calciustepts, and Tarnab soil series to study the effect of different levels of humic acid (HA) derived from lignitic coal on the growth of maize (Zea maysL. Kissan). HA was sprayed on soil at the rate of 0, 50, 100, 150, 200, 250, and 300 mg kg−1 soil along with uniform dose of nitrogen–phosphorus–potassium (NPK) (120–90–60 kg ha−1). The addition of 50 and 100 mg kg−1 HA caused significant increase of 20 and 23% in shoot and 39 and 32% in root dry weight of maize plants as compared to control. The increasing levels of HA above 50 and 100 mg kg−1 produced no significant effect on maize yield. Soil organic matter content was improved slightly (7 to 14%) and pH values were decreased by 0.2 to 0.3 unit by the HA treatments. Addition of HA increased soil N concentration and plant N accumulation significantly over control with no significant differences within the treatments of different levels of HA applied. Soil P concentration improved significantly by the addition of 200 mg kg−1 HA whereas plant P accumulation was not significantly affected by the application of different levels of HA. Micronutrients [zinc (Zn), iron (Fe), manganese (Mn), and copper (Cu)] concentrations of soil and their accumulations by maize plants increased nonsignificantly over control by the application of HA. Laboratory incubation experiment conducted to study the effect of HA on soil biological and physicochemical properties showed that the addition of 0.5 and 1.0 kg ha−1 HA promoted CO2 evolution, increased bacterial population by 355% to 476%, fungi 610 to 716%, and cation exchange capacity of the soil by 13.8 to 28.9%. Results suggest that increases in growth of maize due to HA addition may be associated with the improved biochemical environment of the soil.