The Use Biofertilizers as an Element of Soil Health Sustainability

ByBuyegi George

Introduction

Bio-fertilizers are substances that colonizes rhizosphere or the interior of the plant.

They make use of soil living microorganisms and supply important nutrients such as nitrogen and phosphorus (Bhattacharjee and Dey 2014).

Intro………

Plants need such nutrients for their growth and development.

Therefore bio-fertilizers add these nutrients through Nitrogen (N) fixation, phosphorus (P) solubilisation, mobilizing and stimulation of plant growth through plant growth promoting substances (Bhattacharjee and Dey 2014; Siddiqui 2006).

Intro…………….. Bio-fertilizers are not harmful to the soil or plants,

they are renewable and environmental friendly, They can be used as an alternative to chemical

fertilizers. They restore the soils natural nutrient cycle They build soil organic matter and Promote plant growth and enhance soil health and

sustainability.

Types of bio-fertilizers

Nitrogen fixing biofertilizer; Rhizobium, Azotobacter, Azospirillum, Algal biofertilizes.

Phosphorus solubilising biofertilizer; Bacillus, Pseudomonas, Aspergillus.

Phosphorus mobilizing biofertilizer; Mycorrhiza. Plant growth promoting biofertilizer; Pseudomonas

Nitrogen Fixing Biofertilizers

Nitrogen is highly needed in growth and development of plants. A soil with nitrogen is a healthy soil.

Biofertilizers ensure availability of nitrogen in the soil for the plants to up take.

Rhizobium

Rhizobium fixes nitrogen (N) from 50- 100 kg/ha (Mahdi et al. 2010), they fix nitrogen for leguminous plants such as soybean, groundnuts and fodder legumes such as Medicago sativa.

Rhizobium can fix atmospheric nitrogen in symbiotic interaction with legumes therefore, once legume plants are unavailable in the field the fixation of N by rhizobium is limited.

Rhizobium…

Rhizobium colonizes the roots of a plant and form nodules using strains of rhizobia which in turn act as ammonia production factories (Mahdi et al. 2010).

Rhizobium inoculation is an agronomic practice that ensure the availability of N in the soil, it is used instead of application of N fertilisers.

It increases yield especially in soils that N is limited

Azotobacteria They are mostly found in neutral and alkaline soils. Unlike Rhizobium, Azotobacteria occur in non-

leguminous plants such as rice, maize, sugarcane, vegetables and plantation crops subsequently they do not produce visible nodules.

They colonize roots and can penetrate the root tissues and live in harmony with the plant.

The isolated culture of Azotobacter fixes about 10 mg nitrogen g-1 of carbon source under in vitro conditions (Mahdi et al. 2010).

Azotobacteria

With strain of Azotobacteria, anti-fungal antibiotics are produced and these inhibit the growth of pathogenic fungus in the roots resulting to prevention of seedling death.

Azotobacteria protect plants from Fusarium, Alternaria and Helminthosporium pathogens (Mahdi et al. 2010).

Azospirillum They fix 20-40% of N/ha and produces

substances for growth regulation. They form an interaction with most of the C4-

dicarboxyliac pathway of photosynthesis plants. Mohammadi & Sohrabi (2012) explains that

Azospirillum can fix atmospheric nitrogen without symbiosis, therefore these biofertilizers are non-symbiotic.

Azospirillum Uses ammonium salts as a nitrogen source

(Gharib, Moussa, and Massoud 2008). They can grow and fix nitrogen in salts and

organic acids and therefore inoculation of such biofertilizers is recommended for maize, sugarcane, sorghum, pearl millet (Mahdi et al. 2010).

They can increase up to 30% of yield

Acetobacteria

It is found mainly in sugarcane and fixes up to 70% of the N requirements in sugarcane (Rai 2005).

They are non-symbiotic and grows inside the root as well as stems to some extent.

Fixes the atmospheric nitrogen and this benefits the crop (Deshmukh, Khobragade, and Dixit 2007).

Phosphorus solubilising and mobilizing biofertilizer

Phosphorus is another important nutrient that is limited in its availability to plants following nitrogen.

This is because, plants can only uptake soluble Phosphorus while the available one is usually insoluble.

Therefore, phosphorus solubilizing biofertilizers converts insoluble phosphorus into soluble form HPO4 2- and H2PO4 by secreting acid, this soluble P will be available, and it is mainly done in the rhizosphere.

This is an alternative to phosphorus fertilizers. Bacteria are the most phosphorus solubilizing

agents when compared to Fungi

Strains from bacterial genera Pseudomonas, Bacillus, Rhizobium and Enterobacter along with Penicillium and Aspergillus fungi are the most powerful P solubilizers.

Bacillus can form a stable and extensive biofilm and secrete many antifungal compounds, such as surfactin, bacillomycin and macrolactin, that protect plants against attack by soil-borne pathogens.

Most species of Bacillus can effectively inhibit the mycelial growth of Fusarium oxysporum.

Pseudomonas species are known to increase the number of nodules, dry weight of these nodules, yield components grain yield, nutrients availability especially phosphorus, and uptake are also increased in crops such as soybean.

Siddiqui (2006) reports that Pseudomonas species reduced Trichodorid nematodes density in potato by 56% to 74%.

phosphorus mobilization

The activity of phosphorus mobilization can be carried out by Mycorrhiza which are the root fungus.

Between plants and Mycorrhiza there is a symbiotic interaction whereby the fungus obtains needed carbohydrates from the plant and in exchange the plant gets the necessary nutrients especially phosphorus

nutrients

carbohydrates

Stress resistance

Benefit for both partners

Plant growth promoting biofertilizer

Most of the microorganisms are used in plant growth promotion.

The symbiotic relationship between bacteria, fungi with their host plants mentioned before are all promoting growth.

There are two categories of relationship namely rhizospheric and endophic.

Rhizospheric relationship happens in the rhizosphere and roots of the plant and the host plant form visible nodules to the plant.

Endophic relationship occur in the tissues of the plant and they do not form visible nodules.

These relationships are beneficial to both plants and microorganisms as they live with harmony by supporting each other’s lives.

These biofertilizers differ in their mechanism of plant growth promotion but generally influence growth via P solubilisation, nutrient uptake enhancement, or plant growth hormone production (Bhattacharjee and Dey 2014).

Some of the microorganisms promote growth by inhibiting pathogen infection.

Benefits of using biofertilizers.

They are environment friendly unlike chemical that usually pollute the environment and eventually kills the microorganisms in the soil.

They protect plants from plant pathogens example are the Azotobacteria and Bacillus biofertilizers.

They increase yield for most crops by assuring availability of necessary nutrients to the plant.

benefits,…………… Accelerate plant growth through good interaction

with the plant. Soils retain fertility because, soil will be free from

chemicals. They are cheap when compared to chemical

fertilizers They may protect the plants from stressful

conditions such as drought

What are the limitations of using Bio-fertilizers?

Conclusion The use of bio-fertilizers is essential for soil health.

When compared to chemical fertilizers it is better to use bio-fertilizers.

Bio-fertilizers makes sure nutrients are up taken by the plants. Some nutrients that are limited for plants are made available by the bio-fertilizers.

Nitrogen is limited in most soils but with biofertilizers it is made available through nitrogen fixing microorganism.

Conclusion…….

Apart from nitrogen, phosphorus also which is usually in insoluble form is converted to soluble form, a form that is available for plants to uptake. All these promote soil health sustainability and plant growth.

Moreover, plants are even protected from notorious pathogens through biofertilizers.

Summary of biofertilizers classification

REFERENCES

Bhattacharjee, Ritika, and Utpal Dey. 2014. “Biofertilizer, a Way towards Organic Agriculture: A Review.” African Journal of Microbiology Research 8(24): 2332–42.

Deshmukh, AM, RM Khobragade, and PP Dixit. 2007. Handbook of Biofertilizers and Biopesticides. http://agris.fao.org/agris-search/search.do?recordID=US201300128985.

Gharib, Fatma A., Lobna A. Moussa, and Osama N. Massoud. 2008. “Effect of Compost and Bio-Fertilizers on Growth, Yield and N Essential Oil of Sweet Marjoram (Majorana Hortensis) Plant.” International Journal of Agriculture and Biology 10(4): 381–87.

Mahdi, S. Sheraz et al. 2010. “Bio-Fertilizers In Organic Agriculture.” Journal of Phytology 2(10): 42–54.

Mohammadi, Khosro, and Yousef Sohrabi. 2012. “BACTERIAL BIOFERTILIZERS FOR SUSTAINABLE CROP PRODUCTION : A REVIEW.” ARPN Journal of Agricultural and Biological Science 7(5): 307–16.

Rai, M K. 2005. Microbial Biofertilizers. ed. M. K. Rai. Siddiqui, Zaki A. 2006. PGPR: Biocontrol and Biofertilization Biocontrol and

Biofertilization.

Thanks

In general, there are 6 major steps in making bio fertilizer:

I. Choosing active organisms, For example, decide to use whether organic acid bacteria or nitrogen fixer or the combination of some organisms.

II. Isolation and selection of target microbes, A step of separating target microbes from their habitat. Usually organism are isolated from plant roots.

III. The isolated organisms will be grown on Petri plate, shake flask and then glasshouse to select the best candidates.

IV. It is also important to decide form of bio fertilizer product wisely so that the right carrier material can be determined. If it is desired to produce bio fertilizer in powder form, then tapioca flour or peat are the right carrier materials.

IV. Selection of propagation method, mainly to find out the optimum condition of organism. This can be achieved by obtaining growth profile at different parameter and conditions.

V. Prototype is made and tested VI.Bio fertilizer is tested on large scale

at different environment to analyze its effectiveness and limitability at different surrounding