**2. Organic fertilizers as an alternative to chemical fertilizers**

Heavy input of synthetic chemicals like herbicides, manure, pesticides in commercial agriculture includes ample amount of cash outpouring. Conventional agriculture practice always leads to pollution, soil degradation and health issues [15]. As a plant grows, the major essential seventeen elements along with other are taken up from the soil. The nutrient supply is the major role of soil and as these elements becomes in short supply than restoration is required in the soil for sustainable agriculture. Chemical fertilizers are used to replenish the soil for centuries. But the efficiency of these fertilizers is very low. Around 80–90% of the fertilizers are not assimilated by the plants after application to soil. The remaining fertilizers acts as contaminant and intrude into the environmental bodies [16]. The soil is capable to produce crops in sustainably but the application of various synthetic chemicals led to loss in soil fertility in different parts of the world. There is a huge gap between nutrient supply and nutrient demand. The nutrient in fertilizers was globally supplied in 2014 was 240 million tons while requirement of nutrient was 284 million tones. This results into scarcity in crop production [17]. On the other hand the

#### *Vermicompost for Sustainable Agriculture and Bioconversion of Terrestrial Weed Biomass… DOI: http://dx.doi.org/10.5772/intechopen.100615*

heavy metals are present in chemical fertilizers and prolonged use of these results into adverse impacts on soil property. Plant metabolism is also affected by the accumulation of heavy metals and becomes fatal. The various contaminants from enters into food chain due to application of chemical fertilizers leading to bioaccumulation. The aquatic life of nearby water bodies are at high risk due to eutrophication [18]. Eutrophication is caused by runoff during rain and sometimes irrigation. Nitrogen and phosphorus are the major elements which mostly affect water bodies. Nitrogen in other forms like ammonia finds its way to atmosphere considered as one of the greenhouse gases. Negatively it contributes to global warming. Therefore all these chemicals are harmful to the surrounding ecosystem as well as human, plant and animal health. The mismanaged application of chemical fertilizers in excessive quantity often results into contamination. These contaminants accumulate in water; air and soil negatively affect the environment thus impedes sustainable production of food [19]. With growing demand the transition was seen in last decades from traditional practices to modern practices in agriculture. The prerequisite of inorganic fertilizers was very high wide-reaching to increase agricultural production. The stipulated demand increased for various essential elements in soil from 2015 to 2020. In the coming 5 years the overall fertilizer consumption will be very high. But eventual application of chemical fertilizers increases the chance of environmental contamination. These chemicals also contain heavy metals and other radioactive compounds becomes fatal when enters the food chain and also a major foundation for contaminants which exist in soil and environment for a longer period [16]. Generally by the composition the inorganic fertilizers more or less remain same as compared to organic fertilizers. However organic fertilizers always have advantages over chemical fertilizers both economically and ecologically. In the recent time amendment of soil with organic supplements is gaining tremendous response for the management of soil nutrients and sustainable agriculture [20].

Organic fertilizers are prepared from various organic resources and nutrient composition varies based on the characteristics of the used feedstock [11, 21, 22]. In the recent time on large scale production and application of organic fertilizers have been promoted worldwide. But the resources to prepare organic fertilizers are limited and difficult to meet the demand. Biodegradable organic matter is the major feedstock for organic fertilizer preparation. Organic matters are considered easiest way for nutrient recycling in soil and plants. They act as soil conditioner and dependency on chemical fertilizers is reduced. If the application is adequate with proper guidance to the farmers then small amount of organic fertilizers is enough to meet the requirement of essential elements for drop growth [16, 23]. Among the various advantages of organic fertilizers the major contribution is the supply of macro and micro nutrients, improvement in soil properties, increase in plant nutrient uptake efficiency, increase microbial interaction and also in a barren land it acts as a better amendment to revitalize infertility of the soil. Therefore a mass movement is required to shift in the application of organic fertilizers prepared from various organic sources. The application of chemical fertilizers as in conventional agricultural practices must be discouraged to avoid deterioration of food quality, human as well as soil health [16].

The nutrient level in organic fertilizers is very high. They are considered good soil amendments and also involves in various disease control in plants. Bacterial augmentation, promotion of plant growth, reducing population of nematodes has been observed during application of organic fertilizers. The increased microbial population and improved organic content in soil result into continuing reimbursement in soil fertility. The crop cultivation in organic way always retains stable pH and more exchangeable minerals for plant uptake [24]. The prevention of harmful impact of inorganic fertilizers and long-standing protection to land is possible by

the application of organic manure. Organic fertilizers are generally free of toxic elements and heavy metals. The carbon linkages in these fertilizers make the nutrient ions release slower which consequently perks up the soil physical properties like aeration, water retention and sustainable nutrient supply. This helps in better plant growth [25].
