**4. Effect of organic manures on soil health**

The addition of organic manures to polluted soils has some beneficial effects on soil properties. The most important factor is soil pH that affect solubility of metal, plant nutrient uptake, plant biomass, microbial activity, and many other characteristics [56]. The increase in soil pH, due to manure addition is due to specific adsorption of organic anions on surfaces of hydrous Fe and Al and the simultaneous liberation of hydroxyl ions [57]. Depending upon the compost sources, pH may either increase or decrease. These amendments improved soil physical characteristics such as particle size distribution, cracking pattern, and porosity. Organic amendments are rich source of nutrients like N, P, and other secondary elements like Ca, Mg, and Fe which are required for plant growth and improves the soil fertility status. The essential nutrients in these amendments are in inorganic forms which are released slowly and subjected to leaching loss compared to inorganic fertilizers [58]. The build-up of soil organic matter through the addition of organic manures increased soluble organic carbon, microbial biomass carbon [59], population and species diversity of microorganisms like bacteria [60], soil respiration [61], and the activity of various soil enzymes [62]. The application of organic amendments to soils results in significant improvements in overall soil quality.
