Comparative effects of organic and inorganic amendments on heavy metal co-contaminated soil remediation, reducing heavy metal bioavailability and enhancing nutrient accessibility for maize growth

Many years ago, widespread and ineffective technologies led to significant ecological contamination, primarily due to heavy metals (HMs), particularly lead (Pb) and cadmium (Cd). Plant growth in heavy metals contaminated and calcareous soil is a challenge for all the growers worldwide. Several organic and inorganic amendments are used by researchers in different types of soils. However, their impact on soil contaminated with toxic metals and alkaline in reaction is still unclear. Therefore, the current pot experiment investigates the relative effect of organic (wheat straw biochar and farmyard manure) at 10 and 20 t ha-1 and inorganic (diammonium phosphate and gypsum) at 100 and 150 kg ha-1 amendments on NPK availability, soil organic matter, soil properties, and maize growth under Cd and Pb stress. Highest soil pH (7.61), soil electrical conductivity (0.25 dS m-1), soil organic matter (1.40%), plant height (92 cm), shoot dry weight (41 g), and root dry weight (5.5 g) were observed because of biochar application at 20 t ha-1. While the highest total nitrogen (N) (0.13%), and phosphorus (P) (8.16 mg kg-1) were recorded with diammonium phosphate application at 150 kg ha-1, moreover, application of farmyard manure at 20 t ha-1 increased the soil potassium (K) (108.14 mg kg-1). Biochar application at 20 t ha-1 greatly reduced the toxic metals bioavailability with a high immobilization index, that is, Cd (52%) and Pb (43.79%) lead to lower concentrations of metals in roots and shoots as well. A negative correlation was identified between soil pH, soil organic matter, and soil Cd, Pb, demonstrating the positive impact of biochar in terms of the reduction of toxic metals by enhancing pH and soil organic matter, found to be the most effective amendment for soil improvement and plant growth under Cd and Pb stress condition.