The Effect of Humic Acid and Biochar on Growth and Nutrients Uptake of Calendula (Calendula officinalis L.)

The objective of this study was to evaluate the potential effect of biochar (BC) and humic acid (HA) application on the improvement of plant growth and the acquisition of nutrients by plant roots of calendula (Calendula officinalis L.). A factorial experiment with a completely randomized design was conducted to investigate the HA and BC effects on the growth, physiological characteristics, and nutrients uptake. The BC was applied by mixing dry soil at rates of 0, 20, and 40 g kg⁻¹, whereas the HA was used with irrigation water at concentrations of 0, 250, and 500 mg L⁻¹. The growth parameters (e.g., shoot dry biomass, leaf area, and stem diameters), physiological characteristics (e.g., chlorophyll content, leaf area, leaf water content, and flowering time), and concentrations of some macro- (i.e., phosphorus (P), potassium (K), and calcium (Ca)) and micro- (i.e., iron (Fe), zinc (Zn), and manganese (Mn)) elements in the shoot were determined after a five month-growth period. The results showed that the utilization of BC and HA not only enhanced the plant growth and morphological parameters but also could significantly improve the acquisition of macro- and micro-elements from the soil and transport them to the shoots well. These effects were stronger when both treatments were applied together at a high application rate of 40 g kg⁻¹ BC and 500 mg L⁻¹ HA. The application of these amendments could improve the availability of nutrients and plant growth parameters by improving plant growth conditions and finally affected crop production.