Thanks Dr Dabi  for your excellent response. Yes, on calcareous black soils  ( Vertisols) , occlusion of micronutrients is perhaps the most common phenomenon. We have experienced this in perennial crop like  citrus  where addition of organic manures in good quantity ( 10-20 kg/plant  , 3-6 tons/ha ) is a common feature , consistently over years ( 25-30 years on an average)  plus the litter fall as annual cycle . You just imagine , how much solubilisation would be a possibility. 

Microbes have the ability to diversify according to nature and properties of soil , soil pH is one of them , so microbes would be abundantly availalble , whether acidic or alkaline soil , or even saline soils. Thats  the beauty of the  soil microbial population ., otherwise where from micronutrients like Zn , B , Mo  etc will be available..?

Soil microbial diversity is critical for plant health and productivity as well as human health. By building up soil organic matter through regular addition of all available organic materials including treated human excreta. When we fertilize the soil we feed both soil microbes and crop plants. Microbes near the roots and root hairs (rhizobial microbes) live in symbiosis with plant roots and solubilize macro and micro nutrients from soil minerals and or applied organic and inorganic nutrient sources. If we need nutritious and healthy foods, we have to take care of soil organic matter (quantity and quality) and soil microbial populations.

Soil microbial diversity is critical for plant health and productivity as well as human health. By building up soil organic matter through regular addition of all available organic materials including treated human excreta. When we fertilize the soil we feed both soil microbes and crop plants. Microbes near the roots and root hairs (rhizobial microbes) live in symbiosis with plant roots and solubilize macro and micro nutrients from soil minerals and or applied organic and inorganic nutrient sources. If we need nutritious and healthy foods, we have to take care of soil organic matter (quantity and quality) and soil microbial populations.

Dear Vethaiya,

Thank you for elaboration giving usefulness of application of organic matter to soil and subsequent role of microbes in organic matter decomposition. However, the question floated at this floor is about the quantitative availability of various micro nutrients by soil microbes during organic matter decomposition or other salts/ minerals containing micro nutrients in their structural make up. Any researcher who did work on this aspect is requested to share information/ data with the research community. 

Dear Vethaiya,

Thank you for elaboration giving usefulness of application of organic matter to soil and subsequent role of microbes in organic matter decomposition. However, the question floated at this floor is about the quantitative availability of various micro nutrients by soil microbes during organic matter decomposition or other salts/ minerals containing micro nutrients in their structural make up. Any researcher who did work on this aspect is requested to share information/ data with the research community. 

You have asked a very nice question. Let me at the onset tell you that it is very difficult to make any biofertilizers aimed only and specifically to carry out micronutrient solubilization in soil. However, if one is particular with soil conditioning with proper manures, these phenomena are some what automatic in the soil unless the soil is virtually deficient in any particular mineral providing a specific micronutrient).

Just a curious tough: 

- "Solubilisation" in the case of inorganic materials/substances ?

- "Mineralisation/decomposition/degradation/" in the case of organic matter?

Dear Dr. Bouabid:

Actually there is a very thin difference between solubilization and mineralization.

However, decomposition and degradation does not necessarily mean solubilization or mineralization.

I appreciate the concerns of Drs Vethaiya , Nazir, Rachid , Jai Ghosh , and get the discussion forward . We often use the term like phosphate soulubilizer , having capacity to solubilize /mineralize an  insoluble/organic source of phosphorus. In this process , is there a possibility for otherwise immobilized form of iron ( For example ) to be solubilized simultaneously . Or alternatively , there could be some iron specific , manganese specific , zinc specific microbes etc. , if streamlined , could more  effectivel y aid in enriching the available pool of  such crunch micronutrients in soil? . And , chronic  problem like lime -induced iron deficiency  , could receive some forward  thrust across the crops ?

ICAR- IIHR has commercialized the Arka Microbial Consortium (AMC) , which contains a Bacillus aryabhattai strain with excellent P and Zn solubilising abilities. CRIDA , Hyderabad, had released an bioinoculant (P.putida) exclusively for Zn solubilization. These are two instances I know.

Thanks Dr Govindan . Any  thing more if you can add , especially with respect to their specificity for substrate . Are they exclusive Zn solubilizers ?.

Dr Govindan , lets expand the discussion  . Very few researchers address such issue which has such  a huge potential in the context of micronutrient nutrition , irrespective of crop and soil.

Zn solubilizer  biofertilizer  is already there in the.market.I like the second statement of Dr.Jai Ghosh that simple addition of manure automatically  does the job of solubilizing micronutrients.I shall be glad if some body explains how the microbes influence/alleviate the lime induced iron chlorosis.

Thanks Dr Rao . Intensive organic  manuring is more or less  a common feature in most of the perennial  fruit crops , but still large scale micronutrient deficiencies continue to hamper the prospect of good fruit yield. If addition of organic manures could alleviate the multitude of micronutrient deficiencies  by solubilizing the native nutrient sources of soil , it will be wonderful experience for the persuit of  perennial crop husbandary , to say the least .

Organic manuring, how much intensive it may be, cannot supply all the micronutrients in required quantities because such quantities may not be present in a manure under consideration. That is why still deficiencies in perennials occur.

I will always go by published literature and scientific reports.Can any body provide some published work where continuous organic farming or integrated nutrient supply  system did not increase micronutrient status of soils.

Thanks Dr Hani for elaborate response. This is not the focus of our discussion . If by inoculating a soil with phosphate solubilizers , there is a simultaneous increase in availability of other nutrients like Fe , Mn , then why shall we tagg  such versatile microbe as phosphate solbilizer , better call them nutrient solubilizer. And in that context , exclusive Fe solubilizers , Zn solubilizers etc are distinctly missing.Such microbes are  not microntrient substrate specific. The most of the reported works are the secondary effect of primary inoculation. Despite these rigorous monitoring for potential harmfull accumulation  of some minerals as a result of application of organic manure ( Farmyard manure ) , we could hardly find any  such harmful accumulation , instead micronutrient deficiencies continued to block the  optimum productivity in perennial fruit trees. I agree with Dr Nazir in this regard. Dr Selvakumar is right about some Zn solubilizers. 

Dr.Srivastava,if understand well,do you expect primary  and independent  inoculates  for elements like Fe and Mn solubilization whose availability in soil  mainly depends the on redox conditions in soil?

I will try to at least partly answer my question.Apart from Fe ,N(NO3),Mn(MnO2),S(SO4) and P(iron phosphates)participate in the reactions(Redox reactiions and pH changes) governing Fe availability.These reactions facilitate the availability of Mn and P also.Under aerobic conditions,mineralization (through participation of aerobic microbes )and chemical  processes release the micronutrients and P.Under anaerobic conditions obligate and facultative anaerobes  oxidise organic mater utilizing the NO3,MnO2, FeOOH depending on the redox potential of the soil.So under prolonged waterlogged conditions the availability of both Fe and Mn will increase.Reduction of Fe compounds also increase the soluble P also.So the Fe availability is decided by the interaction of Fe minerals,other nutrient ions,microbes(through organic acids and siderophores) plant root exudates(phytosiderophores,organic acids and flavonoids).As I understand single microorganism independently can not soluble iron in soil.Some attempted organisms will through light on this. Thiobacillus ferrooxidans(Acidithiobacillus ferrooxidans),thiobacillus thiooxidans and thiobacillu s acidophilus produce organic acids and solubilizeZn,Cu,Fe, Co etc.These are now marketed as Zn and S solubilzers .Also the first organism is also being marketed as iron solubilier.A fungal culture,Pencillium citrinum is attempted as Mn solubilzer.It also acts through production of organic acids.Microbiologists can through more light on these aspects.

I will try to at least partly answer my question.Apart from Fe ,N(NO3),Mn(MnO2),S(SO4) and P(iron phosphates)participate in the reactions(Redox reactiions and pH changes) governing Fe availability.These reactions facilitate the availability of Mn and P also.Under aerobic conditions,mineralization (through participation of aerobic microbes )and chemical  processes release the micronutrients and P.Under anaerobic conditions obligate and facultative anaerobes  oxidise organic mater utilizing the NO3,MnO2, FeOOH depending on the redox potential of the soil.So under prolonged waterlogged conditions the availability of both Fe and Mn will increase.Reduction of Fe compounds also increase the soluble P also.So the Fe availability is decided by the interaction of Fe minerals,other nutrient ions,microbes(through organic acids and siderophores) plant root exudates(phytosiderophores,organic acids and flavonoids).As I understand single microorganism independently can not soluble iron in soil.Some attempted organisms will through light on this. Thiobacillus ferrooxidans(Acidithiobacillus ferrooxidans),thiobacillus thiooxidans and thiobacillu s acidophilus produce organic acids and solubilizeZn,Cu,Fe, Co etc.These are now marketed as Zn and S solubilzers .Also the first organism is also being marketed as iron solubilier.A fungal culture,Pencillium citrinum is attempted as Mn solubilzer.It also acts through production of organic acids.Microbiologists can through more light on these aspects.

Very good Dr. Subba Rao. Nutrient availability is very complex and many factors control the mechanisms of nutrient uptake by crop plants. Role of soil microbes is very critical, but there must be sources of micronutrients available for them to work on.  Applied microorganisms have compete with native microbes that will decide the effectiveness of applied microbes. We need to study more.

Yes, that is very important that sources of micronutrients must be present or added externally for microbes to work and make these available.

Anoop Sir,

I appreciate your concern sir.  It is true that microbes have definite role in micro nutrients solubility in soil which make them available to  plants. During the process of microbial growth,  so many excretory products are going to be released  by these microbes (B, V, F including AMF). Enzymes and chemicals released by them need to be studied for solubility of micronutreints.  Putting specific microbe at different levels in soil will have varied influence on soil properties including micronutrient status. Here bio-carbon status also needs to be estimated. Those need to be correlated for knowing the influence of microbes. 

Thanks for lighting the research!

Our B.arybhattai strain is not exclusive for Zinc, It solubilizes Zn and P , through its secondary metabolite production. Hence we always claim Zn and P solubilization, since the mechanism is almost similar. My classmate Dr.V.S.Saaravanan, proved in 2003 that the Zinc and P solubilzing mechanisms of Gluconoacetobacter are same. With the exception of Zn which can be taken care of by a good acid producer, we should focus on Fe and other elements where a change in the redox status of the element is involved.

I have come across few articles where siderophore production by bacteria has improved the iron nutrition of plants. Even we have published an article on the increase in physiologically available iron status of plants, what is intriguing is the role of microbes in elements like Mn, B, etc

The subject has opended up so wide and so interesting  that now many of us would like to participate more intensively . And . beginning of it started from our studies on response of Pseudomonas on the phosphate solubilization , where there was higher DTPA-Fe , -Mn, -Zn availability . This prompted us to feel for the  exclusive micronutrient solubilizing microbes , which are so limited . Most of you will agree that such microbes by and large , are not substrate specific ( Means microbes  using  micronutrient as a   metabolic  fulfilment of sinks present in such microbes)   . However , some  of the exclusive species of micronutrient solubilizing  microbes  could be highlighted as : Thiobacillus ferroxidans as Fe-solubilize, Penicillium citrinum as Mn- solubilizer ,Bacillus aryabhattai as P- & Zn- solubilizer,   Pseudomonas  putida as Zn-solubilizer . In this context ,  the contribution of  Dr Rao and Dr Selvakumar is appreciable . I request  my other colleagues  to further  share their views , which is truly a marvellous discussion  

Anoop Sir,

This Dr.RAJ from UAS Dharwad.

Sir I am adding little more information to my earlier discussions. Mycorrhiza in soil are well known which influence the solubility of Zn, Mn, Cu and Fe. They alter the oxidation-reduction process. Siderophores which are secreted by microbes are able to complex ferric iron.  Bacteria are able to mobilize metals.

More  at : Ioana Adriana Stefenscu, Raluca Mocanu, M. Duncianu, 2010,

BIO-SOLUBILISATION OF BACILLUS MEGATERIUM OF SOME MICRONUTRIENTS.  Cercetări Agronomice în Moldova Vol. XLIII , No. 2 (142)

Thanks

I understand from some literature that under low P environment( in soil) the Pseudomonas spp. produce siderophores for mobilizing  and complexing P their own  requirement and compete  with other  other microorganisms .How much P will be left for the plant is a question.Some of the siderophore producing Pseudomonas Spp. are disease causing organisms in human beings and animals.How to take care of this aspect.Some microbiologists may give their views.

True Sir, some of the best bioinoculants are also opportunistic human pathogens e.g. P.aeroginosa is an excellent siderophore producer but also a human pathogen. One has to exercise caution at the screening level itself to eliminate such undesirable strains. 

But,  how to address  this this issue . A microbial strain/species once  declared responsive to plant growth  and consequent improvements  soil fertility associated changes , should now follow which course of  further action . And while screening  stage itself, what care,  one should take , can you  elaborate  further on this issue Dr Selvakumar . 

The simplest way to eliminate such strains post screening , is to get them identified by sequencing of the 16S rRNA gene, and based on the % identity, refer their risk classification as per international standards. By this simple process we can eliminate most undesirable strains. I have attached an article on biosafety issues of novel inoculants for your reference

That's fine Dr Selvakumar . Such options are for those who have such techniques to sequence  them through 16S . At the field level , is it possible to discern strainal variability , from ones who are plant specific to ones being opportunistic  human  pathogenic .

That's fine Dr Selvakumar . Such options are for those who have such techniques to sequence  them through 16S . At the field level , is it possible to discern strainal variability , from ones who are plant specific to ones being opportunistic  human  pathogenic .

 In the absence of a taxonomic identity it would be  difficult at the field level.  A simple but crude method would be to avoid isolates that grow luxuriously at 37oC

Excellent  Ratan . I appreciate your concerns.  Surely, rhizo-competent microorganisms have the potential to act as an effective bio-surfactants for the phylloplanes  as well rhizoplanes.  This will be an effective pre-amptive measure to improve upon the micronutrient- use- efficiency . Actually, I flagged off this issue to explore the possibility to streamlining some exclusive class of micronutrient solubilizing microbes on the lines , we talk for N, P like nutrients.   You can add your further feedback please.

Ratan , can you share some of your prominent observations?. This will help other colleagues to fine tune ( If required ) your programme further , and at the same time , get some new ideas , who knows /. 

Intersting Ratan . The basic reason for conventional chelators like EDTA and DTPA were not so persistently  effective due to their higher stability constants, not so easy to get dissociated before entering into root symplast .Use of  biosurfactant such as Rhamnolipid as a lipophilic complex synthesized by Pseudomonas has proven three- to -four times more effective in Zn absorption by the  Citrus sinensis roots. Such information surely opens up  newer field of Zn-solubilisation through complexation .This is what , the very purpose this discussion . And we have been discussing till now about  the secondary role those microbes , which are primarily solubilizer of one nutrient , the consequential effect is on the solubilisation of other nutrient (s). Hope , I am taking the right meaning of your stand Ms Ratan . You  have opended up the subject , from an entirely new angle.    

Rattan , we are looking for some aggressive siderophore producing Pseudomonas and AMF as  well , which would be able to maintain relatively  higher available micronutrient indices  of soil , besides having an excellent complementarity .  I hope, such association will be even effective under soils having higher calcium carbonate .   

We carried out some stdies on nutrient-microbe synergy through in-vitro studies after screening some rhizo-competent microbes while developing rhizosphere specific microbial consortium. It was simply eye opener to all of us. Psedomonas could show colony growth  upto 600 ppm of zinc sulphate , 800 ppm of ferrous sulphate , 600 ppm of manganese sulphate and upto 1200 ppm of urea through Bauyers hole test .And almost similar responses , we got for Bacillus polymyxa. Such studies strongly show the presence of very strong sinks for such micronutrients , which could strongly enrich plants rhizosphere. Doesnt it throw some light that there could be possibility combined use of inorganic fertilizers and such rhizo-competent microbes as a strategy of rhizosphere engineering microbially.

Dr.Srivastava, it would be more  appropriate to express the nutrient concentrations in elemental form rather than salt or fertilizer form.Have  you followed up your lab studies with field studies?Have published these results in any journal?

While screening for Zinc solubilization, I would prefer to get the final stamp of approval from ZnO solubilization since the percent Zn is highest in this salt and the ability of an organism to release soluble Zn from this substrate would be the ultimate

These rhizo-competent   microbes  in consortium mode  , we have tested them in nursery plants , and they are showing very good growth  response of the seedlings. They are equally effective in grown -up orchards in combination with both either exclusive chemical fertilizers or with vermicompost . The only care , we have taken , that we applied microbes in consortium mode first , then applied inorganic fertilizers after 10-15 days. Interestingly , these microbes  ( As broth )when run through drip  irrigation , produced equally good response , but again kept the time interval of 10-15 days between the two sources , in order to harness the  good response. This work very soon , it is coming in form of publication in Communications in Soil Science and Plant Analysis.  

Dr Selvakumar  nice input , you have provided , but  we tried these fertilizers wilifully, since these are  the common fertliizers frequently used in meeting the nutrients requirement of different fruit crops including citrus.

Ms Ratan , these studies , we are talking when we conducted them in-vitro. Where from , these microbes  will accumulate heavy metals when they are in so trace amount in normal agricultrural  soils , and above all the soils are non-contaminated. However , this could be a good option to study in contaminated soils. We have tested in-vitro response of microbes using all conventional fertilizers being practiced.  

Dear All,

I'm interested in the topic but from the "ecosystem functioning" point of view. It seems that indeed fungi act as deliverers of several important nutritional elements, especially N,P, K and Cu (considering non Cu-contaminated environment scarcity of Cu may be limiting for an organism's development). I did one work considering the role of fungi as deliverers of nutrients for xylophages and more deep studies are on their way. I think this study (link below) may be inspiring for you.

Kind regards,

Michał Filipiak.

Article How to Make a Beetle Out of Wood: Multi- Elemental Stoichiom...

Yes  Michal i agree with you fungi are very strong group pf microbes capable of solubilising not only nutrients like P, Fe, Mn, Zn , but can go beyond it theough ecosystem sustainability in terms of expanding the soil carbon sink capacity. We will be happy to listen from you still mor.

My idea in brief is that non-living part of soil is a sink rich in the elements you are talking about. Fungi are able to dissolve non-organic matter, incorporate these nutritional elements into their bodies and use them to build organic molecules. Thus fungi are link between organic and non-organic part of the environment, they put important nutrients to the environment and distribute the nutrients inside ecosystem. I was studying these phenomenon for last few years and I will give you detailed description in my future works.

Michal , could you further supplement your response , with specific reference to micronutrients . Have you isolated some effective strains of fungi  solubilizing micronutrients like Fe, Zn  or Cu as a matter of fact . What was the turnover time of the fungi to be really effective  a  link between organic and inorganic part  of the environment ?.

No, we focus on fungi as a whole group, no strains,  there is a lot to be done. 

I also can not give you precise answer considering turnover time. This would need a laboratory study where one offers to fungi specific pools of elements allocated in organic/inorganic substances. And I would like to see such a study. 

Dr Rao Sir, I am very happy to see the information given by you about Thiobacillus ferrooxidans(Acidithiobacillus ferrooxidans), thiobacillus thiooxidans and thiobacillus acidophilus which produce organic acids and solubilize  Zn,Cu,Fe, Co etc.These are now marketed as Zn and S solubilzers. It is also being marketed as iron solubilier. Sir, can you give the address from where we can get it.

Can we use cow dung micro flora  to solubilize metal oxides to convert micro nutrients. ??  (at farmer level) 

 Can you plz suggest the expt. procedure for  microbial solubilization of micronutrients (farmer level) so our organic farmer can  use the method for making these micro nutrients.

Amit , you can use the mciroflora isolated from cow dung , but not exactly the cow dung as such  , since it may potentially damage the crop , unless well  decomposed. The best course , I would suggest to have well composted manures  mixed with basic micronutrient source  and microbial cultures or rhizosphere soil from within the perimeters of trees ( As a bioinoculant in the absence of specific microbial cultures )  , marinated together for 7-10 days  , and finally to be added within the trees perimeters . This is what we have been adopting in perennial trees  at the farmers level.  We still feel  , very limited microbial inoculants are commercially available  in the market .  We still feel microbes used as phosphate solubilizers  have very good potential to mobilize the immobilized form of micronutrients through popular processes like solubilisation , chelation etc .  , including the phytosiderphores formation  

Dear Dr. Singh I am not aware of the addresses of Biofertilizer manufacturers.Either search on internet or contact National Centre of Organic Farming or regional Centres of Organic Farming or see their website.

Yes, it is very important to talk about PSM, mycorrhiza, and K-mobilizing organisms.....

I appreciate your feedback on the issue, Pulak. Thats the reason , we keep saying , such microbes are not so strict on the basis , we usually define them. For example,  PSM will also mobilise nutrients like Fe , Mn, Zn  into the intensity pool of the soil.

Really useful initiative. There is a huge scope of working on this issue

Thanks Vinod Kumar . This is the very purpose of such platform to have multiple views and  have uipdates  from each others experiences. Unfortunately , this is the issue , we always address indirectly , as a secondary effect of microbial inoculation .

Thanks to everybody for the wonderful discussion! I just want to ask, when you say solubilize, do you mean - directly available to plants? I know that there are instances in which the micronutritient will be made directly available to the plant (?mycorrhyzal fungi), but other instances where the bacteria/fungus has to be consumed by a predator (for example nematode) so as to release the nutrients. In fact, I was wondering is anybody of you acquainted with the research of Dr. Elain Ingham about the soil foodweb. She hosts lectures to farmers based on her research on soil microbiology and emphasizes its importance for soil health. She talks about specific exudates that the plants release in order to attract microbes, which will eventually provided the plants with a particular essential element. Based on her research of soil microbiology relative to ecological succession, she also gives practical advice on what is the optimal fungal to bacterial biomass ratio for growing different crops.  It turns out that different biomes are characterized by different F/B ratios. (read for example here - http://www.rain.org/~sals/ingham.html). Here is her CV with a list of publication on her website - http://www.soilfoodweb.com/drInghams_cv.html .  I will be very happy to hear additional comments! Dr. Srivastava, thanks once again for initiating the discussion!

I agree. Besides, microbial immobilisation and root exudates helping nutrient availability, depending on resultant soil pH, ameliorants influence nutrient solubilization. For instance, if acidic conditions develop, availability of otherwise insoluble cations increases. Creating acidic micro-sites by appropriately combined and compacted NPK sources have been found to be a practical route enhancing nutrient use efficiency. My message is that for bringing un-reached sources within the reach of plant roots, in addition to harnessing microbial industry, significance of chemical routes need also valuation. Good discussion, congratulations for flagging the issue.           

Thanks Christopher for wonderful response . And , so sorry to respond to you so late . When  we say , solubilised form , as evident from the increase in their concentration  in the extractant , we are using to estimate , is supposed to be available to plants. However , it remains to be seen , what is the fate of such elevated concentration nutrients in soil solution phase, what proportion of this , is immobilised by the microbes , chelated and later used by plants . If bacteria and fungus are consumed by their predators , what will ahppen to the total nutrient sink of the soil , since these microbes do act as strong sink for nutrients applied from outside sources? I will be happy , if any one can spill some thoughts on these issues..

And , i do agree , every plant manufactures microbes within its rhizosphere , called biome , as a function of its metabolic activity. 

I think that plants only nurture the multiplication different types of microbes in the rhizosphere by exuding nutrients and other chemicals to attract the required microbes to multiply and work on the substrate to release or immobilize the nutrients, as the case may be. It is a mutually beneficial relationship between plant roots and the soil microbes. The microbiome is highly dynamic and is changing fast to meet changing requirements of plants and microbes. A lot of the interactions is yet to be unearthed to fully understand these interactions. Thank you. 

Thanks so much Dr Katyal  , your feedback on the issue is very forthcoming , considering the fact that  large proportion of applied phosphorous , zinc , iron is diverted towards  unreached sources , these rhizosphere  inahabiting microbes could play an important role in not only making the them as reachable sources to plants  , but  could well expand the microbial diversity. What could be the effective ways to expanding the profile of soil microbial diversity ..?

Thanks Dr Balasubramanian . Nature and properties of root exudates  as per crop species  define the  rhizosphere mcrobial  diversity , both structurally and functionally . Our emphasis of discussion was to streamline , why dont we have strict Fe-solubilisers , Zn -solubilisers, Mn-solubilisers ..etc ..with whatever  understanding , we have right now on soil microbial-plant  interaction .

Dr. Srivastava, Good question indeed!

No doubt, the co-precipitation followed by occlusion of micronutrients in CaCO3 concretions in soils gives us a focus area for research work. I believe that solubilization can be used to improve micronutrient availability in calcareous soils.

I am not convinced if microbes can help solubilize the micronutrients in slightly acidic red soils. 

Thanks Dr Dabi  for your excellent response. Yes, on calcareous black soils  ( Vertisols) , occlusion of micronutrients is perhaps the most common phenomenon. We have experienced this in perennial crop like  citrus  where addition of organic manures in good quantity ( 10-20 kg/plant  , 3-6 tons/ha ) is a common feature , consistently over years ( 25-30 years on an average)  plus the litter fall as annual cycle . You just imagine , how much solubilisation would be a possibility. 

Microbes have the ability to diversify according to nature and properties of soil , soil pH is one of them , so microbes would be abundantly availalble , whether acidic or alkaline soil , or even saline soils. Thats  the beauty of the  soil microbial population ., otherwise where from micronutrients like Zn , B , Mo  etc will be available..?

Yes, Dr. Srivastava. 

I don't know much about this but my opinion still says that availability of Zn, B and Mo is mainly guided by soil chemistry, not microbial biochemistry.

I would like to know if you have some reference to disprove my belief. I will be more than happy.

Regards,

MKD

Dr Dabi , take simple inoculation of Pseudomonas , we very often see not only increase in P-availability , but nutrients like Fe, Mn, Zn as well .  the  same , you will see in case of Am-inoculation . Why does it happen ...? Have  a look please..

Absolutely correct, Dr. Srivastava!

In your example Zn, Mn and Fe are occluded and co-precipitated in Ca phosphates such as DCP, TCP and OCP. Once Pseudomonas was added, resultant acidity solubilized the phosphates with consequent release of the metals mentioned above.

This does not emphasize microbiology but pure soil chemistry because any source of acid other than Pseudomonas would make the same result.

The idea behind my previous statement "I don't know...that availability of Zn, B and Mo is mainly guided by soil chemistry, not microbial biochemistry." was to mention that microbes might not "directly" participate in "cycling" like they do for N, P and S.

I hope I could express my notion.

Regards,

MKD

Interesting . How does this reaction take place ..? That was the  basic premise of question , microbes directly or indirectly have the ability to bring the insoluble sources into soluble forms , thereby , elevate the pool of available micronutrients in soil . no , doubt microbes have much greater role to play in cycling of nutrients like N, P, S . I agree with you on that score.

I think any acid-causing microbe would do that unless it is hostile for native soil ecology. 

If we look at Iron, Manganese, and Zinc the alkaline and high carbonate soil environment will cause potential for plant deficiencies. However, in Alkaline environment Molybendum will be more available and the acid environment will be one giving potential for deficiency. In these cases the gross amount of nutrient is not so important as the availability issue which can be related to pH and other factors. The ability of mycorrhzal fungi to extend the root by 2 to 3 magnitudes and appears to be critical for micro and macronutrient issues. In some ways they seem to sense the need and expand according. In extremes of alkalinity and acidity the mycorrhizal will adjust in agreement with signals received from the plants.  The adjustment of real deficiencies and excesses work together with biology which has been much neglected by those aligned with a strictly chemical viewpoint. Biology and chemistry must be viewed as complements not competitors to reap the best return on our investments. 

Well said Dr Hepperly, likewise different microbe also sense nutrient deficiencies signals and reorient different strains of microbes in response to changing soil environment. Dr Dabi, hope we can take some clues from these responses.

We can not separate the biochemistry with microbiology whenever we talk of microbial solubilization of the nutrients . For example adsorption of Boron on organic matter, unless organic matter is microbially decomposed, how will Boron release into soil for plant uptake. 

Let me add few more of my experience on microbial solubilisation of micronutrients. 

Rhizobacteria ( Psedumonas , Aeromonas , Arthrobacter , Bacillus, Streptomyces0 producing Fe-chelating compounds or siderophores like hydroxate , catechol, pyoverdins, are known  to sequester Fe from soils . The stability of siderophores is highly pH dependent , ( for example hydrocimate siderophores  are stable at pH 3-4, while catechol is stable at pH 7.5-10).

Rhizobacteria that are active in supply of Cu are Pseudomonas , Bacillus, Sphingomonas, Arthrobacter, Stenotrophomnas, etc , and  also act in antural phyremedaition process in polluted soils. thtas how they maintain homeostasis in rhizosphere. The other group of rizobacteria comprising Rhizobium , Acinobacter ,Pseudomonas , Bacillus etc are also considered proficient in Zn-solubilising capacity .

Bacterial genera like  Pseudomonas , Bacillus, Heptothrix, Citrobacter, Acidobacter, Nitrospira, Firmicutes , are known in making Mo availble to plants an dtrapping the excess Mo , if any . Mo is sequestered similarly like Fe by mo-binding siderophores , and , therefore, facilitate towards the uptake under limiting conditions.

Boron is tighighly held by organic amtter , and B could be released into the soil solution with decomposition of organic amtter . Gypsophila , Bacillus, Microbacter  sequester B by forming unreactive precipiatate in mineral form with Fe , Ca, or PO4, at pH 8-9 . B-solubilising bacteria like  Arthrobacter , Rhodococcus, Gracibacillus, Lysinibacillus, and Algoriphagus  are known to be efficient microbes .

Hope ,  Rajakumar , Dr Dabi , Dr Hepperly , Deka, Shirgure , Malhotra  and other colleagues will find it interesting . . 

Microbes have role in creating better nutrient pool in soil, some play direct role while others play indirect role.  Boron solubilisation could be one such example.

We should never see soil ecology , biochemistry and microbiology in isolation , lets use them in complimenting each other , much to the benefit of crop in sustaining the productivity on a long term basis, besides  avoiding any possible nutrient mining