**3. Organic soil amendments**

Organic soil amendments have been widely used to binding heavy metals by changing their forms from initially highly bioavailable forms to the much less bioavailable fractions associated with organic matter (OM), metal oxides, or

*Remediation of Soil Impacted by Heavy Metal Using Farm Yard Manure, Vermicompost, Biochar… DOI: http://dx.doi.org/10.5772/intechopen.105536*

carbonates [24]. These amendments have significant binding effects on heavy metals because it contains humic acids which bind with a wide variety of metal(loid) s including Cd, Cr, Cu, and Pb [25]. The commonly used soil amendments which are organic in nature are composts of different origins, manures, sawdust, sewage sludge, and wood ash [26]. The two major advantages of these amendments as compared to other soil amendments are relative of lower cost and they commonly facilitate the re juvination of contaminated soils. However, the residual effect of organic amendments on metal solubility should also be considered. Metal extraction depends upon the original OM content, the soil type, and the rate of OM transformation over time [27]. This is the important consideration that addition of a single organic amendment results in the production of many different organic substances. This is because, during the break down of organic matter, various organic acids are released which may alter metal availability [28]. Increased decomposition of OM decreased the surface area and CEC, this is due to an increase in dissolved organic carbon which results in the release of metals [29, 30]. Thus the nature and stability of OM amendments are also important for determining the long-term partitioning of metals between the solution and the solid phase. Various organic manures are used for remediation purposes like FYM, vermicompost, biochar and Poultry manure. In this chapter, the effect of organic manures on the remediation of heavy metal contaminated soils will be discussed one by one. Let us discuss them one by one:

#### **3.1 Farm yard manure**

Various organic amendments were used to remediate heavy metal contaminated soils like farm yard manure and composted organic amendments, The effect of organic manures to be applied depends upon the nature, mobility, and the bioavailability of metal, its microbial decomposition, and its further effects on soil chemical and physical proprieties [31]. Using amendments in contaminated soils, metal Immobilization is a remediation measure that decreases mobility and phytoavailability of metals in the soils and their plant uptake [32]. It is being used by farmers as source of nutrition to field crops. Low availability of this manure is a major problem on its use as a source of nutrients. FYM controls the production of crop and maintain properties of soil and it can be used to decrease heavy metal stress in plants. The FYM, pig and cow manure decreased available Ni content in soil due to the formation of strong metal complexes with OM [33]. In sandy loam soil, application of FYM significantly reduced Cd and Pb content in the shoots and roots of Amaranth [34]. Due to increased soil pH, complexation of metal with OM and coprecipitation with P content, the metal concentration in tissues of plants for metals (Cu, Zn, and Pb) will be decreased in *Chenopodium album* L. compared to plants grown in compost treated soil or a control soil. A pot experiment was conducted for remediation of Cr in Maize- Indian mustard rotation in two soils (contaminated and uncontaminated soil), the uncontaminated soil was artificially contaminated with Cr levels up 320 mg kg−1 soil and two amendments (FYM and lime) were used for remediation purpose and found that FYM was the best amendment for reducing the toxicity of chromium [35]. In calcareous contaminated soils, the uptake of Zn, Pb, and Cu in Greek Cress will be decreased by 16, 54, and 21%, respectively by application of green waste compost [36]. In wheat, the toxicity of Cd will be reduced by more than 50% by compost application thus decreasing Cd uptake in wheat tissue and hence regulates wheat growth which is primarily attributed to an increase in surface charges [37] and adsorption of metal onto metal-binding compounds such as phosphates and carbonates [38]. Compost contaminated soils may increase the mobility of metals like As [39]. Due to dissolved organic carbon competing with

As for sorption sites and a significant soluble P component, a large increase in leachable As from soil amended with compost was observed due to which, As from organic and inorganic binding sites are displaced [40]. On the other hand, biosolid compost has also a positive effect to remediate an arsenic spiked contaminated soil. In the mining and agriculture sector, manures and composted organic amendments have also been used as soil conditioners [41] and the physical properties and nutrient status of mine soils are significantly improved [42]. By aerating, heavy metals are also removed. Aeration helps microorganisms to decompose the pollution by making nutrients available to the plants. Plowing up to lower layers also exposes some pollutants to the sunlight and this can help as well.
