Microbial Inoculants: an Approach to Sustainable Agriculture

originally an article published here by Sunita Gaind, i thought i'd repost it, given there's a wealth of good information on the subject, which gives a broad overview:

The green revolution though made India self sufficient in food production, but at the cost of soil health. Persistent use of chemical fertilizers and low input of organic material in soil reduced its organic matter content, resulting in stagnation of food grain production by 1.5 %.

To restore the productivity of soil, efforts need to be focused on use of natural resources that can be an alternate to costly chemical fertilizers and restrict soil impoverishment. Current developments in sustainability involve the rationale exploitation of soil microbial activities and use of less available sources of plant nutrients. Nitrogen and phosphorus are the macronutrients that limit the plant growth. To meet the crop need, these are generally supplemented through chemical fertilizers. Soil inhabits microorganisms that possess the particular trait for nitrogen and phosphorus transformation. Their application to soil under crop cultivation can improve the nutrient availability; reduce the input of chemical fertilizer and a way to sustainable agriculture.

What are microbial inoculants?
Microbial inoculants are the formulations of beneficial living microorganisms that when added to soil, directly or indirectly, improve the nutrient availability to the host plant and promote plant growth. Microbial inoculants for biological nitrogen fixation are both strain and crop specific. However, phosphorus solubilization and mineralization can be mediated by potential isolates of bacteria and fungi. The latter being the key components of soil plant system can be developed as phosphate solubilizing microbial inoculants.

Fungi vs Bacteria as Phosphate solubilizeres
 Fungi maintain their P dissolving efficiency even on repeated sub culturing
 The extracellular production of phosphatase and organic acid is higher with fungi compared to bacteria. Therefore, fungi are more effective phosphate mineralizer/ solubilizers compared to bacteria.
 Their hyphae can travel long distance in soil more easily than bacteria and can prove more beneficial for solubilization of phosphorus in soil.
 They can tolerate low moisture, high temperature, heavy metals and agrochemicals.
 Their spore forming nature is an additional advantage for their survival under environmental stress.

How do microbes improve the availability of nutrients?
Soil microorganisms are involved in large number of processes that affect the P transformation and influence its availability to plant roots.
 By the excretion of hydrogen ions.
 By release of organic acids.
 By production of phosphatase enzymes that can mineralize soil organic P.
 Chelating metal ions that may be associated with complexed forms of P or may facilitate the release of adsorbed P through ligand exchange reactions.
 By displacement of sorption equilibria that results in increased net transfer of phosphate ions into soil solution or an increase in the mobility of organic forms of phosphorus.
 Growth stimulation through production of phytohormones.
 By production of siderophores.
 Phosphate dissolving fungi may also provide micronutrients for formation of polyphenol and other aspects of phenolic metabolism.
 Phosphate dissolving Trichoderma harzianum has shown the ability to accelerate the oxidative dissolution of metallic Zn.
 They also provide disease resistance to plants due to production of antibiotics and protection against soil borne pathogens.

Phosphate dissolving microorganisms used as microbial inoculants
Fungi: Aspergillus awamori, Aspergillus niger, Penicillium digitatum, Pencillium radicum, Penicillium bilaiae, Trichoderma koningii

Bacteria: Pseudomonas striata, Bacillus polymyxa, Bacillus megaterium, B.subtilis, B. circulans

Carriers: Charcoal- soil mixture, vermiculite, press mud, peat, cow dung cake powder, farm yard manure, wheat bran etc. Amendment of charcoal soil - mixture carrier with calcium alginate resulted in better retention of moisture.

bacteria may help improve one of the world’s most important food crop

Scientists in Canada are showing the way to a sustainable future for farming.  At the university of Guelph, research  is continuing into the beneficial role microbes may play in a post-peak oil world.

from: this page on their website

Inoculating corn seeds with “good” bacteria may help improve one of the world’s most important food crops, according to a University of Guelph professor.

Manish Raizada, Department of Plant Agriculture, says adding useful microbes to corn might be cheaper and more sustainable than expensive chemicals to help plants use nutrients or fight diseases or pests.

Raizada recently surveyed “good” bacteria living in ancestral and modern corn grown across North America. Completed with recent PhD graduate David Johnston-Monje, this study appeared in PLoS One. The research was supported by the Ontario Ministry of Agriculture, Food and Rural Affairs, the Ontario Ministry of Research and Innovation, and the Canada Foundation for Innovation, among others.

“We have found and cultured collections of microbes that might be providing different corn with beneficial functions,” said Raizada. “We will be determining if these microbes can be useful incoculants, or biofertilizers, for corn and other cereals.”

Raizada said breeders and agrifood companies might use the results to pack useful bacteria into corn and other cereal crops.

Scientists already knew that bacteria live in corn and other plants. Like the group of microbes in your gut that help digest and absorb food, certain types of bacteria in plants and seeds appear to help the plant survive by, say, making essential nutrients available, Raizada said.

Different corn types carry varying groups of beneficial microbes, but some of the good bacteria have been lost during 9,000 years of human cultivation in North America.

The Guelph researchers set out to determine what good bacteria remain, and where they are found. They looked at 10 kinds of corn and four teosintes (forerunners of domestic corn). They chose varieties between southern Mexico, where people began to cultivate the crop thousands of years ago, and Quebec’s Gaspé region, where First Nations people domesticated a type of corn only hundreds of years ago.
“As indigenous peoples have selected and bred corn plants, they unknowingly have also selected and cultivated microbes,” said Raizada.

They found some bacteria were conserved in all corn types. Others were found only in certain kinds of corn. One microbe in a giant Mexican variety makes a chemical known to promote plant growth. Another bacterium makes a hormone that stimulates roots, which might help a corn variety grow aerial roots to support and nurture itself in swampy conditions.

Raizada plans to test the effects of those bacteria, and that of another fungi-fighting microbe, in Guelph field trials. The researchers will also study such basic questions as how these bacteria move within plants and soil.
Reintroducing microbes into corn may be a good alternative to chemicals, Raizada said. Each year, Canadian farmers already use at least $100 million worth of biofertilizers to help corn plants use nitrogen.