**Abstract**

The role of microorganism is very critical in nutrient management of horticulture and plantation forestry. They are conductors of the nutrient management orchestra as they provide by inputs in terms of micro and macronutrients besides organic matter and can be called as bio-inoculants (biofertilizers). Biofertilizers play a vital role in fixing the atmospheric nitrogen and mobilization of phosphorous, sulfur, manganese, copper, and iron in the soil. Symbiotic (Rhizobium and Frankia) and nonsymbiotic microorganisms (*Azospirillum*) are known to improve the soil fertility by fixing the atmospheric nitrogen. Arbuscular mycorrhizae fungi (AM fungi) and phosphobacterium have ability to transfer insoluble phosphate into soluble form. Moving in this direction it becomes imperative to understand as forest microbiologist and pathologist, the roles played by microorganism in diverse plantssoil-microbe interaction to analyze their effectiveness in improving their efficiency. Biofertilizers are economy and environmentally safe, and there is a growing awakening among the tree growers and farmers. In agriculture, advantages of biofertilizer application are better known, but in tree crops, the utility of biofertilizers is still in an experimental stage. The review paper is collective evident for the compatibility of different biofertilizers and their augmentation effect on the production of quality seedling and nutrient management of tropical horticulture and plantation forestry.

**Keywords:** arbuscular mycorrhizae fungi (AM fungi), bio-inoculants (biofertilizers), horticulture, plantation forestry, sustainable nutrient management, Rhizobium, Frankia

## **1. Introduction**

Plants are being an important component of socio-economic condition of human life and culture. Ever since the beginning, tree crops have furnished use with three of life's essentials, wood, food and oxygen. Besides these, they provide additional necessities to human being such as shelter, fuel wood, fodder for livestock, ethno medicine, architectural, agriculture implements, building construction tools, sound and wind barriers, soil improvement through litter production and nitrogen fixation in association with Rhizobium and Frankia. Many drugs which derived from plants generally have been replaced by more potent synthetic ones and trees remain a source for some drug ingredients for pharmaceutical industry. They play an important role in ecosystem services through carbon sequestration, improving air quality, climate amelioration, and conservation of water and supporting

wildlife. They also reduce the atmospheric temperature and the impact of greenhouse gases by maintaining low levels of carbon dioxide.

Plant growth and productivity is generally regulated by the availability of soil nutrients. One of the major efforts to increase the plant productivity is through management of nutrients, which can be achieved by application of fertilizers. However, application of chemical fertilizers is not eco-friendly and economically viable in current scenario. Other alternative method is supplement of bioinoculants (bio-fertilizers) for sustainable development of horticulture and forestry crops. Bio-inoculants are plant growth promoting beneficial microorganisms such as the species of *Azospirillum, Azotobacter, Bacillus, Ecto and Endo-mycorrhizal* fungi*, Frankia, Pseudomonas, Rhizobium*, *Trichoderma,* etc. Such microorganisms accelerate certain microbial process to augment the extent of availability of nutrients in the form, which can be assimilated by plants and also maintain the plant health by controlling diseases.

#### **2. Rhizosphere and microbial interaction**

Various types of microorganisms inhabit air, water and soil. They play an important role in restoring the physical, chemical and biological property of soil. Rhizosphere ecology and microbial interactions are responsible for key environmental processes, such as the bio-geo chemical cycling of nutrients, organic matter and maintenance of plant health and soil quality [1]. Among the microbial population, both beneficial and harmful bacteria as well as fungal species were found, but the microbial population was low when compared to rhizosphere soil [2].

Rhizosphere is the physical location in soil where plants and microorganisms interact. The interest in the rhizosphere microbiology derives from the ability of the soil microbiota to influence plant growth and vice versa. The presence of microorganisms in the rhizosphere will increase root exudation and it was found that 5–10% of the fixed carbon was exudates from the root under sterile condition, on the introduction of beneficial microorganisms, root exudation rate increases by 12–18%. The interaction between bacteria and fungi associated with plant roots may be beneficial, harmful or sometimes neutral for the plant, and effect of a particular bacterial species may very as a consequence of soil environmental conditions [3]. The beneficial microbes can be divided into two major types based on the living nature; free living (that live in soil) and symbiotic relationship with the plant root nodule of legume and actinomycete plants [4].

#### **3. Bio-inoculants**

Bio-inoculants are beneficial microorganisms for nutrient management, plant growth and are eco-friendly and natural inputs providing alternate source of plant nutrients, thus increasing farm income by providing extra yields and reducing input cost also. Bio-inoculants increase crop yield by 20–30%, replace chemical N and P by 25%, stimulate plant growth, enhance soil biodiversity, restore natural fertility and provide protection against drought and some soil borne plant pathogens. The role of bio-inoculants has already been proved extensively in enhancing the mineralization processes of organic matter and helping the release of nutrients, utility of soil organic matter contents and cations exchange capacity [5] and therefore, bio-inoculants are gaining importance in agriculture for the past few decades. However, the scientific exploitation of bio-inoculants in horticulture and forestry is scanty in developing countries like India.

**273**

*Sustainable Development of Horticulture and Forestry through Bio-Inoculants*

1.Nitrogen fixing symbiotic microorganisms (*Rhizobium* and *Frankia*)

2.Nitrogen fixing non-symbiotic microorganisms (*Azospirillum, Azotobacter* and

3.Phosphate solubilizing microorganisms (*Arthrobacter, Pseudomonas, Bacillus,* 

4.Phosphate mobilizing microorganisms (Ecto and Endo—Mycorrhizal fungi)

6.Sulfur uptake (*Pseudomonas, Klebsiella, Salmonella, Enterobacter, Serratia* and

7.Zinc solubilizer (*Bacillus subtilis, Thiobacillus thiooxidans* and *Saccharomyces* sp.)

9.Plant growth promoters (*Pseudomonas* sp., *Bacillus* sp., *Serratia* sp.)

Plant growth promoting rhizobacteria are group of bacteria that actively colonize roots and increase plant growth and yield [6]. It enhances plant growth and productivity by synthesizing phytohormones, increasing the availability and facilitating the uptake of nutrients by decreasing heavy metal toxicity in the plants, antagonizing the plant pathogens [7]. The mechanisms by which PGPR promote growth are not fully understood [8], against phytopathogenic microorganisms by production of siderophores, the synthesis of antibiotics, enzymes and fungicidal compounds [9] and also solubilization of mineral phosphates and other

*Azospirillum* species are free-living N2-fixing bacteria commonly found in soils and in association with roots of agriculture, horticulture and forestry species [11]. *Azospirillum* are known to act as plant growth promoting rhizobacteria (PGPR) and stimulate plant growth directly either by synthesizing phytohormones or by promoting improved N nutrition through biological nitrogen fixation (BNF). PGPR also produce several the growth promoting substances including IAA, GA3, Zeatin and ABA [12]. Presently there are seven species have been identified in this genus, *A. amazonense* [13]*, A. brasilense, A. lipoferum,* [14]*, A. doebereinerae* [15]*,* 

Applications of plants with Azospirillum have promoted plant growth of agronomically important field crops by 10–30% in the field experiment [19, 20]. Nursery experiments proved that the inoculation of tree cops with *Azospirillum* could result in significant changes in various growth parameters, particularly shoot and root growth, biomass, nutrient uptake, tissue nitrogen content, leaf size of several shola tree species [21] and *Casuarina equisetifolia* [22, 23]*, C. cunninghamiana* Mig. [24]*,* 

**4. Classification of bio-inoculants for tree crops**

5.Potash mobilizer (*Bacillus* sp., *Pseudomonas* sp.)

**5. Plant growth promoting rhizobacteria (PGPR)**

*A. halopraeferens* [16]*, A. irakense* [17] *and A. largimobile* [18]*.*

8.Iron uptake (*Pseudomonas fluorescens*)

*DOI: http://dx.doi.org/10.5772/intechopen.87148*

blue-green algae)

*Aspergillus*)

*Thiobacillus*)

nutrients [10].

**5.1 Azospirillum**

*Sustainable Development of Horticulture and Forestry through Bio-Inoculants DOI: http://dx.doi.org/10.5772/intechopen.87148*
