Role of organic and inorganic amendments in alleviating heavy metal stress in oilseed crops

Oilseed crops are grown worldwide and considered as one of the most important crops due to their economic importance.These crops mainly include rapeseed, mustard, sesame, groundnut, sunflower, safflower, soybean and cotton. Heavy metal pollution is one of the main concern in many industrialized community around the globe, particularly in those areas where untreated waste water is released frequently from industries and used to raise agriculture crops. The heavy metal such as Cd, Pb, As, Cr etc are not required for any known biological functions, but some heavy metal such as Zn, Cu, Fe, Mn etc are required in minute quantity for normal plant growth and development but slightly higher concentrations of these metals are toxic to plants. Metal concentrations in plants vary with plant species, age, tissue type and the forms of metal in soils. Higher concentration of metals in plants could reduce plant growth by interfering biochemical processes such as photosynthesis, respiration, water relations, reproduction, and could cause changes in organelles by disruption of membrane structure and functions, oxidative damage and lipid peroxidation and alteration in chlorophyll contents. Chemical immobilization is in-situ remediation strategy where inexpensive and easily available chemicals are used to decrease plant availability of metals in contaminated soils. In general, chemical amendments are of two types i.e. organic and inorganic. These amendments are quite effective in immobilizing metals, thereby decreasing their plant bioavailability. Organic materials mainly include farmyard manure, biochar, low molecular weight (LMW) organic acids and plant growth regulators. Inorganic materials include silicon (Si), inorganic fertilizers like di ammonium phosphate (DAP) and potassium dihydrogen phosphate (KH2PO4). It also includes liming agents like CaCO3 and CaO and S-containing compound like hydrogen sulfide (H2S) and elemental sulfur (S) etc. These materials could transform metals into low soluble forms owing to precipitation as sparingly soluble compounds, thus decreasing metal absorption by oilseed plants at soil level and enhanced different mechanisms at plant level to counteract metal toxicity and translocation. This chapter covers the aspects how to restrict the entry of heavy metals in oilseed crops by the use of different organic and inorganic amendments and their effect at both plant and soil levels.