**4. Types of soil amendments**

Soil amendments are generally added to soil for reclamation process which improve soil physical, chemical and biological properties. Soil amendments can be inorganic and organic resources. The most preferred soil amendments include natural minerals like gypsum, pyrite, lime; other amendments from biological origin such as animal manures, compost, vermicompost, farm yard manure etc. are organic in nature. Organic amendments generally used in arable lands are derived from agriculture, forestry sources and urban areas. In agriculture, animal manure is the most common source of amendments from animals, like cattle, buffalo, goat, poultry etc. Inefficient utilization of nutrients (viz., N, P, K, etc.) and rainwater by oilseed crops are mostly associated with low soil organic matter [32]. Therefore, addition of organic amendments stimulates microbial activity which releases organic acids and other metabolites that reduce nutrient sorption and enhance availability of nutrients (P, K). Addition of inorganic amendments such as gypsum, clays like bentonite, perlite etc., lime, sodium chloride, epsom salt, sulfur minerals etc. are allowed in soils reclamation with some restriction and are mostly based on site specific management practices. Thus, the two most common soil amendments used in agriculture are described below.

a.*Organic amendments*: Organic amendments are usually derived from live sources and natural sources of carbon for micro-organisms. Soil organic amendments are generally derived from variety of sources such as plant origin, animal manures, crop residue or waste parts, green manures, forest system, urban wastes, agroprocessing wastes etc. Among these the most common organic amendments used in agriculture consists of animal manure which can be fresh, composted, liquid or solid fractions etc. from various animal species. Other organic resources include crop residues such as straw, grain husk, legumes, sometime mushroom spent wash. Forest origin amendments mostly includes, wood shavings, wood chips, sawdust, deink sludges, leaves etc. Industrial wastes such as coir-pith waste, sericulture waste is known to tremendous amount of nutrient content. Urban wastes mostly includes the organic fraction of municipal solid waste, sludge waste, industry waste are rich source of nutrients but are used with restriction as organic amendments in crop fields [33]. Interestingly, biochar is yet another and famous organic amendments gaining popularity in agriculture and other fields. Addition of microbial inoculants or biofertilizers are effective amendments for improving oilseed production by enhance biological N fixation

in legume oilseed crops, uptake of nutrients, efficient utilization of water directly influencing yield. Treating legume oilseeds with rhizobia and P fertilizers improved soybean grain yield because P availability enhances N assimilation from atmosphere by root nodules [34].

b.*Inorganic amendments*: Inorganic amendments are either mined or man-made in nature. Inorganic amendments most commonly used as soil conditioners are lime and gypsum. Beside these, basic slag, sulfur, perlite, bentonite clays, Epsom salt, sodium chloride, etc. are other inorganic source of amendments. These minerals naturally occur in earth and can be used to improve soil physical chemical and biological properties especially by adjusting soil pH. Amendments such as gypsum are commonly used to rehabilitate saline-sodic soil supply S nutrient and alleviate salt stress. Gypsum is oldest soil amendment, important source of Ca and S commonly used for crops. Besides natural mine gypsum, flue gas desulfurization (FGD) gypsum is also used as soil amendment available as by-product from coal-fired power plant to remediate saline-sodic soils [35].
