**5. Soil properties as influenced by soil amendments**

a.*Chemical properties*: Combined use of organic amendments such as FYM, compost, vermicompost, green manures etc. with chemical fertilizers are essentially required to improve soil health. Addition of soil organic amendments result in carbon accumulation and enhance SOC content in long run for sustaining any cropping system. Organic amendments such as FYM, composts, CR can sustain SOC at higher levels in soil as compared to mineral fertilizers. Soil organic amendments effect pH and cation exchange capacity, which indirectly influence essential nutrient bioavailability thereby direct impact on soil fertility [47]. Composition and maturity of soil amendments significantly influence soil reaction. Some amendments have high Ca or basic cations which results in 'liming effect' of soil thus increasing soil pH [48]. Thus liming improves soil microbial activity and diversity in acid soils. On contrary some organic amendments reduce soil pH which is attributed to either humic acids released during carbon pool degradation and /or by nitrification of ammonium in the amendment [49]. Blanchet et al. [50] reported that addition of FYM and CR amendments with reduced mineral fertilizers improved SOC by 6.2 and 2.4% respectively over only fertilizers plots after 50 years of cropping. Application of these organic amendment improved C/N ratio, available P and K content. In soybean crop,

*Soil Amendments: An Ecofriendly Approach for Soil Health Improvement and Sustainable… DOI: http://dx.doi.org/10.5772/intechopen.106606*

addition of 5 t ha−1 FYM with RDF increased grain yield by 13% over the control [51]. Improvement in crop yield with organic amendments application could be attributed to increased N supply directly and indirectly improving soil environment for plant growth. Organic amendments such as FYM, animal manures etc. contain varying amount of N, P, K and other nutrients. Among nutrients, N amount and availability is associated with the type of organic amendments added to soil which undergoes mineralization to provide available N to crops. Organic manures or compost supply N, but slow mineralization by micro-organism limits its availability in short-term. However, with continuous application of FYM, compost etc., builds up N and residual effect on N availability is usually visible after 4–5 years [25]. Depending upon the origin and type of organic resources, variable effect is observed on soil pH. Long term application of organic amendments was found to decrease [52] and increase [53] soil pH in many studies. Chemical properties like cation exchange capacity improves with addition of FYM, biosolids etc. Beneficial effects of FYM and phosphocompost with recommended fertilizer doses in soybean crop on significant improvement on SOC, N, P, K and S availability in vertisol has been reported by many researchers [54]. Organic amendments regulate P and K supply by (i)chelating with Al, Fe, Ca ions thus decreasing precipitation of P and enhancing P availability; and (ii) reduce K fixation, solubilization and release slowly K by organic-clay interactions. Application of biosolid-municipal waste compost once in 4 years improves P supply in soils [55]. Beside enhancing nutrient availability, soil amendments viz., organic manures/ compost improve rain water use efficiency of oilseed crops by increasing moisture retention capacity of soil [56].

b.*Physical properties:* Soil amendments, both organic and inorganic alter soil physical properties supporting both chemical and biological parameters in improving soil health. Organic amendments, in particular improves soil structure, better soil aggregation, enhance water holding capacity, maintains optimum soil temperature, reduces bulk density (BD), increases porosity favorable for extensive root growth and development to extract plant nutrients. Moreover, organic amendments stimulate microbial activity, secretion of exopolysaccharides improve soil structure, other compounds like hyphae enhances soil aggregation and stability. Addition of FYM with fertilizer dose, decreased BD significantly compared to only fertilizer plots [57]. This decrease in BD is due to higher pore space, organic carbon, better aggregation, root growth, and micropores in soil amendment treated fields. Application of soil amendments/ conditioners significantly decreases soil bulk density and a decrease in bulk density would be expected when soil is mixed with less dense organic material. Addition of municipal solid waste compost improved water stable aggregate and macro pore distribution, leading to higher hydraulic conductivity of clay loam and loamy sand soils. Microbial respiration improvement with addition of MSW compost directly improved soil structural and hydrological properties [58]. In addition, soil rich in organic matter are less prone to erosion processes than soils with low organic matter those that are predominate in arid and semi-arid areas, the reason being organic matter improves soil structure and tilth as well as it cements individual soil particles into larger aggregates, which leads to less runoff and erosion. The amendments can increase the stability of surface soil aggregation, which has ability to resist movement by wind or water and soil pores created by aggregation promotes water infiltration, thereby reducing runoff and transport

of soil particles with the water, indicating lower soil erosion. Use of agricultural gypsum is one of the alternative to reduce soil density, on reaction in soil solution it acts as a binder by the cations such as calcium and sulfur, which acts to neutralize soils [43]. Crop residues amendments acts as surface mulch, decreasing evaporation and enhancing water retention in soil. When incorporated, CR acts as carbon source enrich soil organic matter, improves soil aggregation, improves water infiltration thereby reducing soil erosion. Addition of 3 t ha−1 mustard CR with gypsum amendment reduced runoff and soil loss by 26 and 29% respectively in soybean crop [59]. CR retention on soil surface benefits (i) protecting bare soil surface against raindrop slashing; (ii) enhancing aggregate stability; and (iii) prevents compaction of surface soils due to rain drop effect [60]. In another study by Soinne et al. [61] reported biochar addition improved aggregation of clay textured soils reducing negative impact of tillage on soil aggregates.

c.*Biological properties:* Soil microbes are crucial components for sustaining soil health as they have affirmative role in enhancing nutrients availability by nutrient cycling through the processes of mineralization and immobilization [62]. Addition of organic amendments improve biological properties by stimulating microbial growth, energy, nutrients, indirectly promoting crop growth and development. These amendments bring biodiversity leading to functional changes promoting plant growth and disease suppression. Furthermore, enhancing structural and functions biodiversity reinforce soil ecosystem, which could become tolerant to natural and anthropogenic stress and turmoil [63]. The presence of active, abundant and diverse microbial community in the soil is an important indicator of improved soil health and agronomic production. Moreover, the activity and abundance of diverse soil microbes govern the stability and function of agro-ecosystems. The activity of soil enzymes is a measure of soil microbial health and is sensitive to various factors including climate, temperature, soil moisture, soil temperature, edaphic properties, crop management practices, etc. [64]. However, the chemical degradation (salinization and alkalization) of soils hinders the biological activities viz. mineralization, enzyme activities, microbial biomass carbon and nitrogen, etc. and lowers the crop productivity. Hence, the application of organic amendments i.e. green manures, crop residues, FYM, compost, vermi-compost, etc. is one of the most suitable management options for degraded soils [64]. The potential benefits of organic amendments in stimulating microbial activities by providing energy and principal nutrients are well recognized [47]. The increased supply of nutrients and growth substrates enhance the numbers of ecological niches and promotes ecological interactions between the microorganisms which may affects the microbial diversity and their abundance [65]. Thus, the increased functional diversity of microbes promotes plant growth, strengthen the soil ecosystem stability and promotes resilience against anthropogenic stresses [63]. The positive role of organic amendments on soil microbial activity, their diversity and composition has been reported in several studies. Organic amendments reduce the soil pH and ESP of the calcareous soil by producing organic acids and increasing the availability of Ca2+ which exchange Na+ of clay particles and create favorable soil environment for microbial multiplication and activity [66]. The application of sesbania green manure increased the soil microbial biomass carbon (SMBC) by 90%, microbial respiration by 104% and DHA by 265% as compare to control along with the increased C sequestration. Similarly, the application of gypsum improved the SMBC by 29.5% over control [66]. The improved biological

*Soil Amendments: An Ecofriendly Approach for Soil Health Improvement and Sustainable… DOI: http://dx.doi.org/10.5772/intechopen.106606*

activities attributed to increased supply of energy from carbonaceous materials, sugar, amino acids and organic acids produced from the decomposition of organic matter and decay of plant roots. Further, the reduced pH and ESP of soil improved the microbial C into the soil [67]. The black soils are very susceptible to degradation and can be improved by applying gypsum together with organic amendments which improve the microbial activity. It has been recommended that application of organic amendments (green manures) is suitable alternative to costly gypsum for reclamation of sodic black soils, enhancing crop productivity and developing a sustainable agro-ecosystem [66]. The quality and quantity of the organic amendments also influence the diversity and activity of microbial community. Meena et al. [68] reported that application of municipal solid waste compost and rice straw compost at a rate of 16 and 14 t ha−1, respectively significantly improved the dehydrogenase, phosphatase and urease activities than control. The combined use of gypsum and bio-organic amendments (compost and crop residues) provides essential nutrients to crops and improves soil biological properties besides improving physical and chemical properties and productivity of saline soils [69]. The structural and functional diversity of soil microbes and bacterial richness and evenness were improved by application of organic amendments to soil [70]. Thus, the organic amendments have been reported to sustain soil health and crop production by improving soil biological properties. Although, the adoption of soil conditioners/amendments should be based on specific crop production standards for developing sustainable agro-ecosystem [71].
