Comparative effects of humic acid and charcoal on soil, growth, and biomass properties of lupine (Lupinus albus L.)

Recently, charcoal and humic acid application in soils is a burgeoning area of research due to its profound impact on soil properties and crop yields. Charcoal contributes to improved soil structure, enhanced water-holding capacity, and increased carbon sequestration while humic acid, a component of organic matter, enhances nutrient retention and availability, fostering healthier plant growth and long-term soil health. The experiments were conducted on November 20, 2022, at Grdarasha Research Station, College of Agricultural Engineering Sciences, Salahaddin University-Erbil, Iraq. Two organic sources (humic acid and charcoal) were used to improve soil chemical properties, growth, and biomass characteristics of white lupines. Humic acid at the levels of (0, 10, and 15 g m-2), respectively along with 1 kg m-2 of charcoal. Results showed that essential elements and heavy metals in soil were increased and improved with adding humic acid and charcoal, and then well-affected root ability to uptake nutrients. The great values of germination rate, leaf number (LN), and fresh and dry shoot weights were found when charcoal was stirred to the soil (83.33%, 15.67 LN plant-1, 10.91, and 2.24 t ha-1), respectively. While the longest root length was recorded when humic acid applied at rate of 10 g m-2 (24.22 cm), it was true about the enhancement of cluster roots. Despite that, humic acid at the rate of 15 g m-2 caused to improve fresh and dry root and shoot weights, which were compared to control treatment. The final results indicated that by adding humic acid (H), and charcoal (CH) could improve soil chemical properties, and then may affect positively microorganisms, which can promote plant growth by transforming, solubilizing, and mobilizing soil nutrients. As well, lupinus seemed as phytoremediation (uptake) in case of some heavy metals.