<p>Long term indiscriminate use of heavy metals (HMs) contaminated wastewater for irrigation purposes leads to build up of higher concentration of HM in soils which will be up taken by food grain crops and ultimately transferred to human body causing bioaccumulation. Biochar, through its high surface area and numerous pores, can be effective in absorbing bioavailable HM, reducing risk of exposure. However, different modification process is used to activate the biochar for better performance and efficiency, in our study we used acid modification using phosphoric acid and a strongly acidic salt iron chloride. Preparation of biochar using invasive weed like parthenium not only reduce weed load of crop field but is economical also due to its easy availability and higher char yield. We used ten treatment combinations of two modified biochar types with unmodified biochar at graded application dose of 5, 7.5 and 10 t ha⁻¹ and one control treatment replicated thrice following completely randomized design. We noticed biochar at the dose of 10 t ha⁻¹ significantly enhanced growth and yield parameters of rice, moreover phosphoric acid and iron chloride modified biochar does this job better even at lower doses of 5 and 7.5 t ha⁻¹ compared to higher dose of (10 t ha⁻¹) unmodified biochar. We noted significant enhancement in soil microbial population after application of biochar and modified biochar, which further enhance different soil enzymes activities related to nutrient cycling as compared to control treatment. Nearly, 1.5 times increment of dehydrogenase, alkaline phosphatase and urease activity in 10 t ha⁻¹ modified biochar treatment was noted as compared to control. Thus, it can be concluded that application of simple and modified biochar was effective in increasing the soil microbial and biochemical parameters in heavy metal contaminated soil.</p>