**5. Production of organic fertilizer and biofertilizer using fungi**

The substances that fertilize the soil can be called fertilizers. Fertilizer is widely used to supply essential nutrients for plants to increase yield. Many types of fertilizers existed such as inorganic, organic, and biofertilizer, fertilizers that provide nutrients in inorganic forms are called mineral fertilizers, and those derived from plants or animal residue are considered organic fertilizers whereas biofertilizers are products containing living cells of different types of microorganisms that have the ability to mobilize nutritionally important elements from non-usable form to usable form through the biological process [46]. Biofertilizer is well known for its application in sustainable agricultural practices it is a cost-effective, eco-friendly, and renewable source for plant nutrition [10, 47], the ability of the fungi to restrict the growth of other microbes and have potential to control the disease of the plant is termed broadly as biocontrol agents, many fungi like *Trichoderma harzianum*, *Ampelomyces quisqualis*, *Chaetomium globosum, C. cupreum*, *Gliocladium virens, Coniothyrium minitans,* etc. are some common example of biocontrol agents and many of the micro and microfungi made the availability of the complex nutritional compounds into a simpler form which is used by plant easily such fungi acts as symbiotic agent. The symbiosis of fungi with the plants helps plants to fix nitrogen, solubilizes phosphate, and other complex compounds of the micro and macronutrient present in the soil as recalcitrants form. Based on the several abilities of beneficial fungi many formulations have been made for the application of the fungal-based biofertilizer in arable soil [48]. Details account of fungi in plant nutrition has been discussed below, production of fungal biofertilizer using mycorrhizal fungi is very selective since AM fungi are obligate symbiotic, they can not be grown without plant host on synthetic media, hence it is produced in association with the host plant. Mass production by pot culture is the most common method used in the production of AM based biofertilizer, no matter what method or formulation is used but for the success of the formulation depends on (a) economic viability of production (b) retention of the inoculum viability after formulation (c) handling and dispersal capacity during application [48, 49]. The formulations are availably available in the form of powder, pellets, gell beads [50]. There are several AM

**Figure 4.** *Gradual conversion of leaf litter into organic leaf compost, arrow indicates the gradual conversion of leaf into matured compost.*

fungi formulations but the efficiency of the applications depends on the products, conditions of the environment, bulking agents, and other variables [3, 10, 47, 48]. However, to produce organic fertilizer the enzymatic system of fungi is used to convert biodegradable substances into compost, in nature, the fungi decompose the recalcitrants substrates into simple form and helps in nutrient recycling. These facts of fungi are used in the production of organic fertilizers, for example, leaf compost where the dead leaf convert into dark brown organic fertilizer see **Figure 4**.

*Trichoderma viride* is a filamentous fungus widely used as a biofertilizer as a biocontrol agent, this fungus nowadays has gained global market attention as a biofertilizer. *T*.*viride* acts as an antagonistic fungus, it is effective in controlling seed-borne pathogens as well as soil-borne pathogens. The working mechanism of *Trichoderma* as a biocontrol agent is either direct or indirect, *Trichoderma* restricted phytopathogens growth indirectly by competing for nutrients and space, by modifying the environmental conditions, by promoting plant growth and by plant defensive mechanism and antibiosis, and directly *Trichoderma* controls phytopathogens by a mechanism such as mycoparasitism [51].
