Influence of biofertilizer on heavy metal bioremediation and enzyme activities in the soil to revealing the potential for sustainable soil restoration

Overuse of chemical fertilizer and pesticides in agricultural activity is frequently damaging to soil health and can accumulate heavy metals in the soil environment, causing harm to plants, humans, and the ecosystem. This study was done to evaluate the effectiveness of biofertilizers in reducing heavy metal levels in contaminated soil and enhancing the activity of soil enzymes that are crucial to plant growth and development. Two bacteria strains, Pseudomonas aeruginosa. and Bacillus firmus, were chosen to develop biofertilizers based on molasses. The pot experiment was setup using a completely randomized design with four treatments and five levels; Bacillus firmus and Pseudomonas aeruginosa were used separately, and they were combined for the biofertilizer dose (20, 40, 60, 80, and 100 mL). Utilizing contaminated soils taken from a greenhouse farm the effect of biofertilizer on heavy metal bioremediation and soil enzyme activity was examined. Methods of soil agrochemical analysis were used to determine the soil physiochemical properties and the concentrations of heavy metals Cu, Fe, Zn, Cd, Mo, Mn, were determined by inductively coupled plasma–mass spectrometry ICP-MS, following DTPA extraction methods. In results, soil pH decreased from 8.28 to 7.39, Ec increased from 0.91 to 1.12, organic matter increased from 18.88 to 20.63 g/kg, N increased gradually from 16.7 to 24.4 mg/kg, and K increased from 145.25 to 201.4 mg/kg. The effect of biofertilizer treatment on soil physiochemical characteristics was significantly positive. Application of biofertilizer significantly increased the heavy metal bioavailability and the activities of soil enzymes. Soil pH were positively correlated with soil Zn (0.99819*), APK (0.95869*) activity and negatively correlated with Fe (0.96759*) also statistically significant at (p < 0.05). The soil Cu positively correlated with Fe (0.99645*), Cd (0.97866*), β.D.GLU (0.99769*) and negatively correlated with PAK (− 0.9624*). Soil ARY had positive correlation with soil Mn (0.99683*), Cd (0.95695*), and negative correlation with PAK (− 0.99424*) at (p < 0.05). Soil enzyme activities were negatively correlated to heavy metals at a significant level. Collectively, the study highlights the potential of biofertilizers as a sustainable and effective approach to enhance soil health and remediate heavy metal-contaminated soils in greenhouses.