Home About us MoEF Contact us Sitemap Tamil Website  
About Envis
Whats New
Research on Microbes
Microbiology Experts
Online Submission
Access Statistics

Site Visitors

blog tracking

Prospects of Marine Biofertilizers for Saline Soil Crop Cultivation
S. Ravikumar
Department of Oceanography and Coastal Area Studies
Alagappa University, Thondi Campus, Thondi – 623 409,
Ramanathapuram District , Tamilnadu, India.
Email: ravibiotech201320@yahoo.com

Soil salinity is a major problem that makes soil unfit for Agriculture. Historical records of the past 6000 years of civilization evidenced that, humans have never been able to continue a progressive civilization in one locality for more than 200 to 800 years. The major reason for the decline of any civilization in any area seems to have been the destruction of the resources base of that area. In Mesopotamia, major salinity damage occurred from 2400 BC to 1700 BC and the slow increase in salinity
caused a decline in agriculture productivity to as approximately as 65% over a 700-year period.

At present salinity is one of the most serious environmental problems influencing crop growth around the world. In India, 7 m ha are affected by salinity and alkalinity and marginal decrease of productivity is expected from these lands. In Tamilnadu coast, salt causes stress and damage on the plant during the vegetation period from germination – emergence through growth – development and harvesting time.

It is generally accepted that three major hazards are associated with saline habitats. These may be described as follows:

(a) Water stress arising from the more negative water potential (elevated osmotic pressure) of the rooting medium.

(b) Specific with toxicity usually associated with either excessive chloride or sodium intake , and

(c) Nutrient ion imbalance when the excess of sodium or chloride leads to a diminished uptake of potassium, nitrate, or phosphate or due to impaired internal distribution of one or another of these ions.

More than that, inoculation of crops with any useful microorganisms would not yield desired success. Excess salts in soil adversely affect the survival, growth and nutrient supply to the plants.

During late 20th century, research has been started to find out the saline tolerant Azotobacter and Phosphobacteria from marine aquatic sediments but focus on the preparation of marine biofertilizer for coastal agriculture has not been made. Recently, identification of saline tolerant biofertilizers for possible utility to use for agricultural crop cultivation has been recognized. Besides that microbial biofertilizers have also been identified to improve the growth of mangrove plants. Azotobacter, Azospirillum, Phosphobacter and Phosphate producing bacteria and Blue Green algae were isolated and identified from saline sediments. Even the presence of high phenolic compounds and prevalent anaerobic condition in the mangrove habitat and their biofertilizer effects have been proved with the rice and balckgram crop seedlings. Compared with the existing biofertilizers the morphological and biochemical characteristics are similar except the saline induced effects on growth and physiology.

Genus Azotobacter

Azotobacters are aerobic, free-living, thermotrophic bacteria with unique ability of fixing atmospheric nitrogen. The bacteria are gram negative, often motile by peritrichous flagella or non-motile. The Azotobacters produce copious amount of capsular slime. They do not or endospores but some species may form cysts. Three species of Azotobacters such as Azotobacter chroococcum, A.berijerinkii and A. vivelandii were identified from mangrove rhizospheresediments. All the three species are able to tolerate high saline concentrations (up to 35 g 1-1 and 30 g1-1). These species of Azotobacter enhanced the germination and growth of rice and black gram seedling even at high saline conditions by fixing atmospheric nitrogen and producing phytohormones. Among them, A.chroococcum was highly recommended than the other bacterial species.

Genus Azospirillum

Azospirillum species are free living bacteria know to fix atmospheric nitrogen. They occur as free living organisms in the soil and are associated with mangrove and associated plant species. Azospirillum are plumpy, slightly curved and straight rods gram negative to gram variable. They are motile in liquid media by a single plar flagellum.

Four species of Azospirillum such as Azospirillum lipoferum, A.brasilense, A.halopreferns and A.irakense were identified from the marine sediments. Of them, Azospirillum lipoferum was found to be the dominant species. All these species were found to have tolerance ability to various salinity levels (0- 35 g.1-1) and grown better in 30g. 1-1 NaC1. However, the level of phytohormoneProduction (IAA) and the rate of nitrogen fixation was better at 10 g .1-1 NaC1 and reduced activity could be observed at higher salinity levels. Moreover all these species could be used as marine biofertilizers. Of them, Azospirillum brasilense are preferable than the other species.

Group Phosphate Solubilising Bacteria (PSB)

Phosphorous is an important limiting nutrients. The phosphate form of phosphorous is one of the least soluble mineral nutrients in soil. The phosphorous content of soils may range up to 19 g k-1 but usually less that 5 % of this is available to the plants and microorganisms in soluble form and the rest 95 % is unavailable being in the form of insoluble inorganic phosphate and organic phosphorous complexes. These forms of phosphorous being held in the sediments far a long time remain excluded from cycling. Microbes play a significant role in the transformation of phosphorous and referred to as phosphobacteria. Eight species of saline tolerant inorganic phosphate solubilizing bacteria such as Bacillus subtilis, B.cereus, B.megaterium, Arthrobacter illicis, Escherichia coli, Pseudomonas aeruginosa, Enterobacter aerogenes and Micrococcus luteus were identified. Of them, Bacillus subtilis was predominantly found in mangrove sediments.

All the nine species could able to grow better at 4 g.1-1 NaCl concentrations. However the phosphatase activity was good at 2 g1-1 NaCl salinity levels. Moreover except Pseudomonas aeruginosa and Micrococcus luteus, all the other species of bacteria could be used as a biofertilizer to enhance the growth of rice seedlings. Of them Bacillus Megaterium could be used as a marine biofertilizer for saline soil cultivation.

Group Phosphatase Producing Bacteria (PPB)

Organic phosphorous in the marine environment is macromolecular and not readily available for incorporation into the marine organisms. So the organic phosphorous compounds are to be preconditioned by extra cellular bacterial enzymes called “phosphatases” for making them available to the nutrient cycles. Three groups of bacteria viz., Pseudomonas, Vibrio and Bacillus were identified from mangrove sediments. Of them, Bacillus cereus was dominant form and the phosphatase activity was also higher. All the three groups of PPB could enhance the growth of rice seedlings at 25 g. 1-1 NaCl level of soil salinity at which the phosphatase activity was significantly high.

Recommended biofertilizers for the saline soil crop cultivation on priority basis.

Recommended crop species
Black gram, Rice
Black gram, Rice
Inorganic phosphate
solubilizing bacteria
Black gram, Rice
Phosphatase producing

Species abundance of saline tolerant biofertilizers in the mangrove sediments

-Phosphate solubilizing bacteria (45%)

-Azospirillum (25%)

-Azotobacter (15%)

-Phosphate producing bacteria (15%)

ENVIS CENTRE Newsletter Vol.6,No 2 June 2008 Back 
Copyright © 2005 ENVIS Centre ! All rights reserved
This site is optimized for 1024 x 768 screen resolution