Soil microbial diversity very much influenced by soil properties like pH, depth, structure, organic carbon and initial soil microbial composition. Its remains to be seen how these soil properties interact with different microbial stains. 

Thanks Dr Shirgure  for setting the whole discussion on such an important issue in a right switch on mode. Hope , our colleagues will take the discussion  further.

Abhishek very useful response alongside PDFs . It will be interesting to thrash out the predominant soil property (ies) in a given soil type , or mineralogical preferences by certain group of microorganisms or even by certain crop prefer certain group of microorganism community . We need to pin point such studies so that crop specific microbes can be isolated to put back into the rhizosphere in order to engineer rhizosphere properties according to crop requirement ?

Soil properties have a strong effect and diversified effects on microbial communities. For example fungi in acid soils and bacteria in neutral to alkaline soils. But we are willing to know is this universally true.

Pierlorenzo another very good response at your end , very practical in nature . But , the very purpose of raising such issue was to identify some of the dominating soil properties which dictate some specific type of soil microbes . For example better development of CFUs  of Bacillus mycoides on illitic soils . Can we cite  such  researched studies?.Soil organic matter will be highly predisposing all kinds of microbes , thereby,  giving total microbial load as such very good.

Thanks Pierlorenzo , your inputs are really very provocative  from discussion point of view. the very reason is , now we look straight for having a crop specific multiple inoculation prospect at one time.

Is there any study dealing with soil microbial distribution on illitic  soils versus smectite soils versus kaolinitic soils?

Prof,

There are many subject specialists who have given their useful comments but I want to add some more which is in my mind.

The soil microbial population mainly depends upon the structure, pH and depth of soil. The Earth have a vast ecology from Artic to Temperate and from Temperate to Tropical in short. If we place a broad view, we can see that as the temperature, pH and structure changes the microbial growth rate also changes.

2ndly in my view the growth is also dependent on the rhizosphere of every plant spp. Under this topic the allelopathic effect lies.

The microbes have a diverse effects on plant growth. In some cases friendly microbes enhances the growth as em bacteria and others causes diseases and decrease the growth. These microbes are also dependent on the circumstances like structure, pH, rhizosphere etc. of soil.

I am attaching two papers which can help the readers in this matter.

well during search I also found another line of discussion which I will apologize from prof, as it will deviate the discussion.

There are also some studies in which I am still blank about the impact of molecular techniques, transgenic plants and microorganisms on soil microbial diversity. Prof and other subject specialists can help.

this paper was having some problems so I am posting it again in the continuity of my previous answer.

Hi Sir,

Soil microbial diversity and soil properties are highly correlated (Positive as well as negative). Soil is heterogenetic in nature and microbes are very dynamic in nature. 

Soil properties are highly important for proliferation of microbial load in particular soil. Because soil is a microhabitat center. Clayey soil (large surface area) gives more room for proliferation (by C availability and stabilization of carbon). Presence of high amount of micro aggregates act as sheet for C supply which will lead to development of microbes. Most of the literature reported that clay loam and sandy clay loam are effective support for microbial diversity especially bacteria.

Exudates, mucilages and secretions of C3 and C4 plant.

like these each property (SOM, C:N ratio, soil moisture, soil nutrient dynamics etc) governs the microbial load in soil.

Dear Anoop,

In my view, first, there is a contradiction in the fact that the soil completely different usages can be fed. As building ground or for agriculture. While in the use as building ground the microbial load be eliminated largely and the pore volume be reduced and therefore produced a diversity hostile condition, in the case of agricultural use the microbial load must be eliminated and the pore space to be optimized. The microbial load can however also degrades with microorganisms, which in turn can increases the diversity. Thus, one can make a connection as follows: A Ground Improvement produced to where you compacted the soil, thus reduces the pore space and hence its permeability.

The microbial load can be reduced by increasing of the diversity, and diversity can be increased, where one the pore volume optimizes and thus the habitat improved.

The soil properties could increased the diversity but also can be increased the microbial load, whichever improvement methods be used and how the soil properties after that.

With this basic understanding it is possible to develop a model.

All the best

Very informative PDfs Abhishek , I appreciate it . There is absolutely no doubt whatsoever , soil microbial load is an authentic indicator of soil health/quality.The question , whether or not microbial load undergo population fluctuation in response to crops grown?

Husain , your thoughts are worth appreciating . Soil microbes play diverse roles with regard to both soil health as well as plant health. Still little is known about the mechanistic insights , how these microbes facilitate such diverse functions in a given microclimate?

Gopinath , I am more willing to look at the formation microbial niche within the rhizosphere of a plant . And , how this microbial niche behaves in response to various cultural practices?. Hope , you will provide us further useful information .

Michael very interesting response indeed. Reducing pore volume will increase the microbial load and decrease the diversity , I agree with you,  thats  not the  exact point , I am looking at . How a variety of crops facilitate the growth  of one microbial community and discourage the growth of another microbial community ?  Is their  any kind of underground communication between plant roots or secretion of certain metabolites as secondary metabolites as communication signals for certain microbes to proliferate?  

My question is how can we increase the microbial diversity and microbial load together in the light of Michael's comments ?

Dear Anoop, Dear Parameshwar

First, thanks for your support. It's not my immediate professional field, indirectly but already. First, it is so that the physical state  of soil has influence on the growth conditions and on the habitat of microbialen community and possibly thus it may affect the interaction. How? I dont know!

From the standpoint of plants, these signals must send e.g. in the form of chemical reagents, which may be adopted or rejected by the microbial community. This can become a symbiosis, that promoted the growth of the plant or not. The exchange of information between plants, eg. of a forest, has been so described. Amazing!

I have attached for you a reference of the Max Planck Society, "Plants talk", however, in German. The Max Planck Society is one of the most prestigious German research companies.

Much success

Thanks Michael for yet another very thought provoking response. Yes, I do agree with you , how a plant changes its inhabiting soil surroundings , develops some microbial population as communicating signals , and eventually plant throws out its growth . I appreciate your line of thought as food for new thought in the context of whole discussion .  Unfortunately the language of the PDF , you enclosed is in German . Let me seek your response and the responses from other colleagues   further :

Do you feel , instead of monocropping , mixed cropping or legume -based cropping sequence will facilitate better microbial diversity?

Do you feel , soil microbial load is a function of root mass as well , which in turn , is a  function of crop species?

Dear Anoop,

I attached for you the abstract of the article in English, "Plants talk".

"Research report 2006 - Max Planck Institute for Chemical Ecology

Plants talk

Authors

Paschold, Anja; Halitschke, Rayko; Kessler, André; Baldwin, Ian T.

Departments

Molekulare Ökologie (Prof. Ian T. Baldwin)

MPI für chemische Ökologie, Jena

Summary

Plants respond to herbivore attack by releasing volatile organic compounds (VOCs) that function as a defense by attracting natural enemies of the herbivore, thereby establishing defensive mutualisms with insects. The fact that plants use VOCs to communicate with insects generates the expectation that they also use VOCs to communicate with each other. Numerous studies have examined the question of whether un-attacked neighboring plants growing adjacently to attacked plants use these VOCs to anticipate future attack and preemptively activate defense responses. Most of these experiments have been carried out under experimental conditions that unnaturally amplify or distort the effects of the VOCs on neighboring plants and none have conclusively identified the active constituents of the VOC bouquet that function as signals. Scientists from the Max Planck Institute for Chemical Ecology in Jena present a new experimental approach to these challenges that allows for the study of plant-plant signaling under natural conditions."

Perhaps it is possible for you to contact the Max Plack society. Here the link: https://www.mpg.de/414573/forschungsSchwerpunkt?c=166022

Perhaps the article can be translated in Institute also with you. Your two questions must be answered as follows: There is a function of the plant species and VOCs.

Best regards

Thanks Michael so much for taking so much of pain for all of us and enlightening us with altogether new concept of plant-to-plant communication through VOCs. Probably , similar analogic conditions do exist for microbes as well to , communicate with each  other , popularly called quorum sensing .  However , it remains to be seen , how plants talk with microbes? Is it through VOCs?

Dear Anoop,

As communicate plants? Plants communicate over the air and in the soil!

Today we know that plants communicate, in fact over the air. Enter volatile organic substances, so-called leaf fragrances (eng. Volatile organic compounds) from. These are received and processed by their conspecifics in their environment.

Researchers found that plants communicate through their roots when they touch, so to each other in contact.

Unfortunately, the roots are not always long enough to bridge the distance to the next adjacent plant. In order to still be able to maintain communication between the plants, serving natural networks, how researchers found out recently. Plants use the fine ramifications of a underground growing (Glomus intradices), to means of chemical messengers to transmit signals to their neighbors and these to warn e.g. also in case of pest infestation.

Obove a short summary of the enclosed literature: “Plants in Dialog - Plants Language for Intermediate”, sorry also only in German.

Best regards

Michael , I am deeply impressed , the way you are expanding the scope of our discussion , worth appreciating . My core enthusiasm is about the role microbes  bridging the gap between the plants ( where plants roots do not overlap).  You have brought up a classical case of AMs , they perhaps  have  the best  communicating  ability   between host plant and mycelial network of AMs through a series of endo-phyto-harmones . AMs also have the ability to form common mycelial network between host plant as donor to inoculated plant as receiver in form of intercrop or vice-versa?. Please throw some more lights on these issues , which will be incredible for our colleagues  involved in this wonderful discussion .  

In this case, We must do the analysis of biochemical response of plants to the cultural practices. Might you aware about quorum sensing (means communication between microbes) by means of signalling each other. Niche development mediated by this process. 

I read some where that beneficial microbes prefer produce certain molecules as PHA or ADH (I do not knoe exactly) which orients all the beneficial together and work on it. Like wise pathogens do the same by other kind of signalling molecule.

Gobinath,  if you recall our excellent discussion,  went ahead on the issue of,  how plants communicate  with each other , especially when , there is a nexus between plant and rhizocompetent microbes and roots system come into picture . How do these microbes communictae with host palnts ?. In this case  also , do you feel quorum sensing operates? or any other mode of biochemical signalling , that remain to be unraveled. And , most interestingly , in the entire process, how some soil properties participate in microbial response?

When we look at how plants and people can communicate, I like to "listen" to the loud signals of hydrangea.

Indeed the flower color is a pH litmus and the above parts mirror the sectoring of pH found in the soil below. Blue areas area pink areas alkaline. This is result of the anthocyanin color change with pH.

Indicator plants are probably not considered state of the art. But so much is possible once we have sense of their signals.

Much of area of acquired resistance points to signaling potential of plant Calcium levels. It appears that pathogens often deplete the Calcium pectate bridges and during this ingress a defensive biochemical cascade occurs. Indeed pH has broad range of impact on many nutritional essential nutrients.

Symbiosis is notable of signaling occurring between the plant to symbionts back and forth. One of the big importance of defensive reactions is that many of these have extremely important nutritional aspects as the phenolic pigments in grapes associated with French contradiction that wine indeed not only takes your mind off getting older but also seems to retard biochemical processes stimulating it.

When I worked in Illinois State Natural History Survey at the University of Illinois Champaign Urbana we would identify trees infected with Dutch Elm disease. We could identify the wilt fungus based on fruity aroma of apples and bananas coming from stem piece colonies. The volatiles are extremely attractive to beetle vectors that spread the disease.

As we understand the levels of communication going on it becomes possible to develop strategies which are cross talks interfering with negative communication and stimulating positive ones.

Serpentine soils give a very unique botanical species composition. The presence of mycorrhizae deal with this. The presence of these species can lead to investigations which will convert the Ni toxicity through Calcitic lime application and balancing of nutrients which provide a more broadly adaptable environment for plant productivity.

Yes prof, you are right, till yet no one knows how these microbes functions in such a micro climate. In my view microbes are very tiny creatures and they can grown anywhere in a proper medium. These plants let them to populate in soil and if there are no plants their population decreases and some fungi produce spores to withstand harsh times and when environment is favorable they can continue their life cycle.

I have studied a very useful conversation and I appreciate the answers from experts.

How does the effect of specific nutrient on the change in soil microbial load or diversity come into picture while evaluating such relation ?

Is there any indicator crop or indicator soil property to ensure the presence or absence of indicator microbe?

This is rather difficult to respond in concrete terms . But , soil fertility constraints do influence the microbial load as well as diversity , and more influenced by the history of fertilization and cropping sequence where legumes must be a part of such cropping sequence. This is the area where we need more efforts to go in , I appreciate your quarry . Any of our colleagues can further supplement  please. However , some clues can be taken from earlier responses  of Dr Hepperly and Dr  Lersow about , how plants do cross talk?

The diversity of soil microbes is a function of the amounts and types of roots persisting in the soil. For this reason mixed perennial forbes are so important to our soil health. The mixed herbs provide a complete diet especially when soil chemistry is adjusted. The recycling of manures into the system which compromised of animal and plant systems is the basis of this diversity. In terms of root secretions and their grass, legumes, composites and other families all can work to together as they do in natural prairies which are the most productive habitats for superior soils. The intensive controlled grazing is also important.

Since pH is such a critical factor I like to start there then red tag the deficiencies and toxicities in the soil. In the last analysis the results over time require time monitoring and the execution of a systematic approach. The diversity is mostly related to system not the inputs per se.

Dr Hepperly , i agree with you , soil microbial diversity is perhaps most  influenced by soil pH , which dictates the whole soil macro-and micro-environment . 

For centuries, biologists have studied patterns of plant and animal diversity at continental scales. Until recently, similar studies were impossible for microorganisms, arguably the most diverse and abundant group of organisms on Earth. Studies carried out by Fierer and Jackson (2005 , Proc.Nat.Acd. Sci.. 103: 626-636) showed  Bacterial diversity was unrelated to site temperature, latitude, and other variables that typically predict plant and animal diversity, and community composition was largely independent of geographic distance. The diversity and richness of soil bacterial communities differed by ecosystem type, and these differences could largely be explained by soil pH (r2 0.70 and r2 0.58, respectively; P < 0.0001 in both cases). Bacterial diversity was highest in neutral soils and lower in acidic soils, with soils from the Peruvian Amazon the most acidic and least diverse in our study. Our results suggest that microbial biogeography is controlled primarily by edaphic variables and differs fundamentally from the biogeography of ‘‘macro’’ organisms. PDF  enclosed for further reading

We still have a limited understanding of the complex response of microbial diversity to organic and conventional farming. Here  the structural response of the soil microbiome to more than two decades of different agricultural management in a long-term field experiment using a high-throughput pyrosequencing approach of bacterial and fungal ribosomal markers is reported . Organic farming increased richness, decreased evenness, reduced dispersion and shifted the structure of the soil microbiota when compared with conventionally managed soils under exclusively mineral fertilization. This effect was largely attributed to the use and quality of organic fertilizers, as differences became smaller when conventionally managed soils under an integrated fertilization scheme were examined. The impact of the plant protection regime, characterized by moderate and targeted application of pesticides, was of subordinate importance. Systems not receiving manure harboured a dispersed and functionally versatile community characterized by presumably oligotrophic organisms adapted to nutrient-limited environments. Systems receiving organic fertilizer were characterized by specific microbial guilds known to be involved in degradation of complex organic compounds such as manure and compost. The throughput and resolution of the sequencing approach permitted to detect specific structural shifts at the level of individual microbial taxa that harbours a novel potential for managing the soil environment by means of promoting beneficial and suppressing detrimental organisms (  Hartman et al. 2015, ISME journal 9:1177-1194).

Hope , these will be useful additions  in the course of whole discussion.

Dear Doctor Anoop Kumar Srivastava,

Enjoy your comments! 

Take a look at Shabaran, M. et al. 2016 Dolomite application enhanced Methane uptake in adidic soil Catena 140.

The limed fields of rice generated over 2 times the soil ammonium and 6 times the nitrate.

It would appear that rather than overwhelm the system by adding a lot of synthetic fertilizer we need to start with a better appreciation of the power of pH.

In this same study while the productively climate was increased the generation of Methane  greenhouse gas plummeted. We think that adding a product is the solution and many times we need to beware because sellers convince us of things that are not necessarily for our long term benefit.

The health of our soil is related to both the overall population and diversity of microflora and this is related to the quality and quantity of organic matter.

Lime is actually relatively cheap and widely available. It has a problem of infrastructure for large scale use in some areas and these need an incentive to make this more applicable.

Even in North America where lime is widely available it is often forgotten.

I liked your Peru examples in the attached publication.

Blessings on you and your House.

Paul

Thanks Dr Hepperly . I too enjoy your excellent responses . With your excellent feedback , two very imminent points strike to my mind . These are : I. microbial diversity , whether or not , undergo any reorientation in their diversity ( For example,  preponderance of one community over other )  upon addition of lime/dolomite , since it will bring an increase in soil pH , and possibly in that process, the structural , functional and metabolic  dynamics of different microbial communities  will be exposed to a new soil environment and II. microbial diversity , to what an extent is influenced  by the history of fertilization .

There is a strong relation between nature and properties of soil and soil microbial load but diversity could be guided by crops and cropping sequences.

The amount of soil organic matter is as Sikha Deka so aptly remarked the consequence of the farming systems employed. As soil organic matter increases in quantity and quality the habitat for soil life expressed in the respiration of the soil profile increases correspondingly. The cycling of the nutrients becomes closed and the productivity of plants and animals increase. Soil respiration increase corresponds with higher soil respiration due to its ability to serve as habitat and nutrient source. Also the water capacity of the soil as well as the air capacity is largely a function of soil organic matter. In real terms soil organic matter really matters. 

Dr Hepperly , a near perfect response . This is what exactly required on field. Soil organic matter having huge cascading effects on large number of soil properties , eventually , ensuring much better crop yield through better understanding on soil ecology.

Dr Hepperly and friends, what is your opinion if we follow a balanced fertilization and integrated crop management strategies with a suitable cropping sequence, we can maintain an excellent soil microbial diversity ? 

Dear Parameshwar Shirgure,

The main cropping system in North America is based mostly on Maize and secondarily on soybean. The inclusion of soybean along side Maize is a great stride along with use of no till and reduced till agriculture.

However, these beneficial practices of themselves do not result in significant recharging of soil organic matter. 

On the the other hand, the use of soil organic focused amendment, green manuring, crop rotation, crop and animal integration can lead to big increases is soil organic matter.

Studies conclusively show that  the farming system can engender a significant increase in soil organic matter this in turn favors the diversity of function of soil microbes.  Focus on soil organic matter and it constitutes an ocean that floats all the agricultural boats.

As soil organic matter is increased there is less need to supplement with fertilizers and pesticides. 

Balancing the nutrient situation in the soil in relation to both deficiencies and toxicities is a key to allowing the biology to increase and result in higher potential for the soil resource. The balancing of nutrition needs to be coupled with a soil conservation and farming systems plan and the results of actions by farmers need to monitored and assessing as an on going process. 

The use of ley farming and the emphasis on legumes is very important and can allow optimized regeneration of soil resources reducing inputs and increasing yield and quality of integrated crop farming. 

Since so much benefit can occur from getting the soil pH optimized and the materials to lime are widely dispersed and not in danger of being over exploited that is a very useful place to start. Acidity and alkalinity issues are common in over half of the global tillable land. 

In arid areas the issues of water is so critical and the sandy soils have little capacity to retain and recycle precipitation or irrigation water. The persistence of soil organic matter is favored with the complex of the soil organic matter with Calcium cations and clay which changes the soil organic gain loss equation. 

The elemental practices of improving the soil can lead to removal of excess Carbon and Nitrogen from the air to the soil not only reducing input additions but also leading to remediation of greenhouse gas enrichment concerns of paramount importance to climate change. 

Hope these thoughts will be useful in your thinking and problem solving process. 

Thats the reason, we keep saying , any agricultural practice (s) leading to an improvement in soil organic matter , will have such a strong cascading effect on rest of the soil physico-chemical and biological properties , that will facilitate maintaining better microbial diversity , besides microbial load. 

Some thoughtful answers Anil Kumar , a soil well supplied with organic matter will read much higher enzymatic activities, a better liveliness of soil to carry out multiple functions as ecosystem. I agree with you , no doubt .

Let us consider how the soil microbial community undergoes reorientation when soil properties change from one set to the another, e.g. change in soil organic carbon content or cereals versus pulses. 

Measuring soil respiration, soil dehydrogenase and phosphatase activity is an important aspect to estimate soil biological properties as it acts as a biological indicator towards soil fertility. Moreover, soil shows better biological activities in the summer in comparison to the other seasons with a positive correlation to environmental parameters indicating that soil biological activities along with the microbial load vary with seasons throughout the year. 

Some  good points by Sosanka, appreciate it , worth considering . Let us know Abhishek , how different crops act as an indicator of predominant microbial community  within rhizosphere ...?

Our studies displayed much higher microbial load of soil in rainy season than either  summer or winter..?. What could be delineating reasons..?

Is it possible to isolate the microbes from gut and casts of earthworm and inject into the plant rhizosphere?

Just too excellent Abhishek , worth reading . 

Earthworms form one of the major soil macrofauna to maintain dynamic equilibrium and regulate soil fertility. The soil volume affected by earthworm activities is called the drilosphere, which is a major soil functional domain. Earthworm activity does not only mediate macroaggregate formation, but also microaggregate formation7,8. Based on thin sections of the earthworm gut, casts and control soil from earthworm microcosms, several studies have shown that during gut transit organic materials are intimately mixed and become encrusted with the mucus to create new nuclei for microaggregate formation. On the other hand, earthworm casts significantly affect plant growth through their effects on microorganisms, aggregation of soil and nutrient supply10. Casts have been shown to have enhanced microbial and enzyme activities and micro- and macro-nutrients11. Many authors have reported the occurrence of several species of bacteria and fungi in earthworm casts. Many cellulolytic, nitrifying and denitrifying bacteria have been observed in earthworm casts. Several workers have found that microorganisms flourish in earthworm casts. Earthworm casts are reported to have  a bacterial count of 32.0 million/g compared to 6.0–9.0 million/g in the surrounding soil.

During formation in the earthworm gut, the ‘would be’ casts are colonized by microbe. It is established that earthworms hold greater diversity of microbes in their gut, which are responsible for various activities, including mineralization and chelation of several ions in the soil. Earthworm casts contain many more microbes than its surrounding soil because the intestines of earthworms inoculate the casts with microbes. Earthworms digest soil microbes selectively30. In a vermicomposting experiment  with L. mauritii, the gut and casting analyses proved the removal of pathogenic Salmonella, Shigella and faecal coliform bacteria in 35 days, whereas Pseudomonas, cellulolytic Bacillus spp. and heterotrophic bacterial populations had increased at the end of the vermicomposting period, indicating the selective nature of earthworms.  

Some interesting facts about the issue Dr Deka and Abhishek....

Thanks Abhishek...

Infact drilophytes are also considered synonymous to plant endophytes. Is there any relation between the two types of endophytes , one derived from inoculated plants to one derived from guts of earthworms....?

For the optimum activity of earthworms their needs are critical. They need have a  moisture and temperature cannot be overly hot environment.

I prefer a legume tree for what I call the earth worm garden as it provides an optimized environment. . Their leaves will also be part of the earthworm feeding. 

The earthworm possess specialized Calcium glands which are critical to earthworm digestion. A near neutral pH with material rich in Calcium are prerequisite along with moisture and not too much compostable material so excessive heat is not generated. Stack material no more than 20 cm depth. To ensure the digestive activity of earthworm the stack material can be supplemented with Gypsum Calcium sulfate. 

Under a legume tree the shallow pile which can be supplemented with Gypsum can be a optimum situation. I put a circle of stones as a proper which serve as refuge for the site.

These earthworm gardens optimize their activity which favor the biological control of pests in the surrounding environment.. Earthworms are the favorite diet of song birds which have pest control roles in the garden. 

Using the casting for tea can be very effective in getting a lot of benefit from small amounts of materials. It is particuliarly useful for starting nurseries and for resolving nutrient deficiencies when used in a targeted way a little gives a lot of effect. 

Grass and clover clippings are optimal for earthworm rearing and use of immature stages vegetative material is especially able to stimulate actinomycetes which are well known for probiotic and biocontrol capacity. 

Use your tree to set up a barn owl house and they will provide rodent control around your property. The ability to use biology will not only reduce environmental issues but give increased performance at lower cost. 

When you do this a side effect is that the tree will flourish which is a key source for overall improvement of the whole area extending outside the crown of the tree canopy itself. The animals are doing practically all the work. Sweet. 

Hope you find value and insight in this experience. 

Dr Paul, role of legumes along with Calcium sulphate is more pertinent on acid  soils. Let us know the strategies to be adopted on alkaline soils ? 

Abhishek, Paul and other friends, how does land uses affect soil microbial diversity. Managing soil microbes spatially is more difficult than managing spatial variability in nutrients. 

Dear Parameshwar Shirgura, Earthworms critically need Calcium and flourish in moist shaded environments without excess acidity. In an acid environment I like to lime with either Calcium Carbonate or Dolomite Calcium Magnesium Carbonate depending on the presence or absence of adequate Magnesium. 

In alkaline environments the common situation is an excess of salts and an alkaline pH in that environment  I like to use pit composting with the drainage directed to a layer of organic material. If excess alkalinity is an issue the use of Sulfur in its elemental form and Calcium sulfate not lime or dolomite is recommended. Whether under the acid or semi arid condition the cultivation of earthworms is best accomplished in the shade. Earthworms are most fond of grass clippings and ruminant manures. Piling should be restricted so excessive heat is not generated as this will curtail the adaptive ability of the earthworms. 

In arid and semi arid environments it very likely that supplemental watering will be required. 

More thoughts on your questions. P

As far as i know there should be synergy trade-off relationship among soil bacterial populations and also with the fungi populations meaning that we should consider any managed approach through the time to make a balanced productive environment for the target crops. So, we are in need of having diversified cropping system to have a diversified bacteria and fungi populations. For example we need to have a balance between moisture and oxygen in the soil to have a increasing trend in soil organic matter by more activity in bacteria fungi populations.

Good points Dr Hepperly and Mehrvar. Unfortunately the earthworm density in cultivated soils is  consistently on decline , primarily due to heavier use of chemical fertilizers. Our major problem with striking a balance between fungal and bacterial population is the difference in their likings for soil pH, on preferring acidic environment , while another microbial community thrives well on alkaline soils..?

, . 

Dear Mohammad Reza Mehrvar, While I agree with your assessment that a diversified microbial flora is favorable I take some disagreement on your assertion that fungal and bacterial components are in trade off or an either or situation. They really do not need to be.

The fundamental work of mycorrhizae and symbiotic biological nitrogen fixation would suggest that symbiosis feeds both the fungal and bacterial populations and has positive relationship to the diversity of fungal and bacterial components. This system does not show an win lose result but rather all are winners. 

Mycorrhizal plants stimulate biological nitrogen fixation through the way they feed the Rhizobial component. Basically the source of this tripartite symbiosis that is plant fungus and bacteria is the ability of the plant and microbes to harvest nutrition from the air and repatriate it to the plant and soil.

Since there is no real deficiency of either Carbon or Nitrogen in the air this is preferred source for the farming system and core for biologically regenerative farming systems. This leads to the feeding of the soil upon which our ultimate nutrient from the limiting component which is water and this is captured and recycled through the carbon in soil. 

The biological resolution is also the most energetically, environmentally and economically feasible solution to the farming woes confronted our modern societies is depending on symbiosis employing both the fungal and bacterial partnerships which are synergistic and not antagonistic. 

The reliance of synthetic inputs is a whole different story since they will reduce the signalling of positive symbiosis. This means some of things that originally were viewed as solving our issues and indeed rather part of our problemizer. Fertilizers and pesticides can easily compromise the key need to rely on mycorrhizae and biological nitrogen fixation.

Good insights on the needs to understand the complexities of these issues are right on point. P

Some good points Dr Hepeprly , appreciate your efforts to unravel the existing complexities associated with  fungal or bacterial population are  in possible trade off .. It will be a more pressing experience to realise any compromise  on use of either fertilizers or pesticides/fungicides, or even both ..

yes. soil organic matter, biodiversity in time and space, I do not know, Sure, any crop species supports more specifically microbial or fungi populations depending on the root distribution, I am not sure about this specific approach   

The extent of soil organic matter will determine the activity of soil microbial flora. Microflora gives room or habitat and nutritional support of board from the soil organic matter. More food and more habitat equals more population. The higher soil organic matters are associated with perennial grass and mixed herbs in prairie where roots are most prolific. These are co evolved with large ruminants and this prairie ecosystem has consistently produced the most productive crop soils. When man mimics the proven natural systems good results will occur. In relation to the compromise between the input systems and biologically based systematic approaches. Fertilization of ammoniated fertilizer will compromise biological nitrogen fixation and high soluble Phosphate change the mycorrhizal susceptibility reducing its ability to be effective through the fungal component.  Pesticides are notable for their inhibition of earthworms take copper, benzimadzole, and atrazine as examples. Earthworm are organisms that are the master recyclers that stabilize soil structure.  Iatrogenic refers to agents to combat an issue that actually engender and cause issues. While ammoniated fertilizer is seen as bastion of increasing crop productivity its long term effect of catalyzing increased soil organic matter decay and reduce the pH leads to poorer inherent fertility over a long term. Short term experiments rarely capture long term negative effects. The root of many of our current agriculture issues are consequences of practices designed originally as panacea to our agricultural issues synthetic inputs are not only not panaceas but in addition are the roots of may compromising issues.  From this base I favor biological solutions of our agriculture issues rather than reliance of synthetic chemical inputs. 

Interesting responses Drs Mehrvar and Hepperly , appreciate both of you for putting up some lively discussion , worth for all of our other colleagues following this wonderful discussion . 

Every plant is said to synthesize the microbial diversity within its rhizopshere according to its metabolic activity , often called microbiome . The characteristic feature of each crop microbiome is the function of species in interaction with soil and climate ...?

Microbiome is most pivotal to soak the negative effects of chemical fertilizers by working as a  nutrient sink , and later deliver the same to plant roots in a much mobilised version...

Let me add another response with respect to effect of different substrates on performance of  earthworms and quality of vermicompost:

Six substrates viz. forest litter; banana pseudo stem, pineapple stover, soybean stover, maize stover and paddy straw were tested in complete randomized design with four replications using earthworm species Eisenia foetida. Higher earthworm density was recorded with pineapple stover. Higher and lower rate of earthworm multiplication was observed with forest litter and soybean stover substrates, respectively. Biomass gain by earthworms was more under forest litter substrate as compared to others. Duration required by forest litter and banana pseudo stem was found the least, while paddy straw required longer duration for vermicomposting. Higher vermicompost yield was recorded under pineapple stover substrates. Mean pH of vermicompost was slightly alkaline with reasonable amount of soluble salts.

Organic carbon content and C:N ratio decreased remarkably at maturity. Organic carbon and C:N ratioreduced by 41.4% and 66.0%, respectively at maturity. The N, P, K, Ca, Mg and S contents increased progressively during vermicomposting period and maximum contents of these nutrients was recorded at maturity. At maturity, N, P, K, Ca, Mg and S contents enhanced by 76.1, 154.5, 54.5, 103.9, 140.0 and 50.0% over initial nutrient contents. Among the  substrates, soybean stover was found more suitable for preparation of vermicompost due to higher amount of N, P and S. The K and Mg contents were recorded highest in the vermicompost prepared from banana pseudo stem and forest litter, while higher Ca content was recorded in forest litter vermicompost. However, forest litter was found more suitable for multiplication of earthworms.

PDF enclosed fro further reading...

The amount of soil organic matter in soil is a function of pH and CEC if the top and subsoil. As soils lose their mineral matter and they become acid the ability of the system to produce most  crops abundantly can be seriously compromised. The ideal situation for accruing soil organic matter is when precipitation and evapotranspiration are equal. This allows that the critical mineral matter in the soils  not  to be readily lost to the system. Over use of acid generating ferilizers can work to age and deplete the soils we depend upon. In many areas liming is common practice but where acidity is most limiting infrastructure and liming are not very much practices due to lack of infrastructure and knowledge. Dealing with the excessive salts in the alkaline condition is also not conclusively practiced despite the growing awareness. 

When conditions are arid salts increase but water is insufficient to generate soil organic matter which is generated from the crop metabolism and excess salt and alkalinity can teem up with micronutrient deficiency to produce a difficult constraint.

On the other hand when rainfall is more that evaporation the loss of soluble mineral material leads to acidity and the development of toxicities and deficiencies.

While we are talking about alkaline or acid conditions the alignment of i) mineral availability, the ii) adjustment of pH and the III)  management of water is critical. In relation to these factors for final soil organic matter concentration. Soils generally are optimized at virgin levels of organic matter which is at 5 to 7%. Many of our cultivated soils have 1% or less soil organic matter. Since soil organic can accrue but in individual layers and in the expansion of the top soil itself this represents a major opportunity to both counteract greenhouse gas issues and increase the quality and quantity of the food we need for our future. 

Soil organic matter serves as a buffer for all the constraints mentioned and in addition it not only increases the ability to mitigate soil constraints but increase the high end yield and quality potential of the system.

Another amazing factoid is that very significant crop and animal stimulation can be had at very low concentrations of soluble humic substance making them potentially very economically useful.

Humic materials have major ability to stimulate the chelation and movement of minerals of little inherent solubility but very plant stimulatory such as Phosphorus and Iron. Humic materials also stimulate the physiological responses of the plants to counteract stress and pathogens. 

Very good points Dr Paul. I still feel soil mineralogy in conjunction with climate plays most important role in defining the microbial diversity in the soil. 

Dr Paul, how to get and where can we get the situation featuring Evapo-transpiraion equal to Precipitation ?

This is the reason Dr Shirgure , we stress so much on soil ecology or agroecology so much so.....which by and large dictates such microbial functions...

Dear Parameshwar Shirgure,

In the United States the prevailing winds are from the West to the East as the currents cross the Pacific Ocean and reach the summits of the Rocky Mountains rainfall reaches a peak on the peaks. In the shadow of the Mountains is a rain shadow where dry conditions prevail as the currents continue moisture picks up and the environment gets progressively moisture in the Middle Zone to the Atlantic Ocean the precipitation and evapotranspiration is similar in value. This results in ability to grow praire grasses the most excellent soils all come for prairies around the world and retain soil minerals. When precipitation exceeds the evaporation as occurs in eastern zones of North America the soil minerals are depleted and the resulting chemistry becomes largely acidic. In the wetter regions it will soil acidity which will be confounding and in drier areas excessive salts and alkalinity will be more prevalent issues. In both cases the principle first step is to modify the pH to near neutral for most crop issues. In both the wetter and drier climates the soils will improve if we can modify the pH to an optimum range and adjust the cropping to optimize soil organic matter levels to virgin soil condition for the soil. 

I think similar gradients and issues are expressed in India but am less familiar and I have seen the same gradients in Island systems such as Puerto Rico and Hawaii which I am much more familiarized with. PRH

We often apply soil amendments to amend either acidity or alkalinity, how does soil amendment application bring changes in composition of different microbial communities in soil ? 

How do you feel, whether or not microbial diversity of crop rhizosphere changes at different growth stages of crop ? 

Good information Abhishek. 

Very good response Abhishek...

Microbial diversity in soil: selection microbial populations by plant and soil type and implications for disease suppressiveness. Source : Annu Rev Phytopathol. 2004;42:243-70.,DOI: 10.1146/annurev.phyto.42.012604.135455

Abstract  :An increasing interest has emerged with respect to the importance of microbial diversity in soil habitats. The extent of the diversity of microorganisms in soil is seen to be critical to the maintenance of soil health and quality, as a wide range of microorganisms is involved in important soil functions. This review focuses on recent data relating how plant type, soil type, and soil management regime affect the microbial diversity of soil and the implication for the soil's disease suppressiveness. The two main drivers of soil microbial community structure, i.e., plant type and soil type, are thought to exert their function in a complex manner. We propose that the fact that in some situations the soil and in others the plant type is the key factor determining soil microbial diversity is related to the complexity of the microbial interactions in soil, including interactions between microorganisms and soil and microorganisms and plants. A conceptual framework, based on the relative strengths of the shaping forces exerted by plant and soil versus the ecological behavior of microorganisms, is proposed.

Microbial diversity drives multifunctionality in terrestrial ecosystems

Manuel Delgado-Baquerizo Source ;Nature Communications 7, Article number: 10541 (2016)doi:10.1038/ncomms10541 Januaary 2016

Abstract:Despite the importance of microbial communities for ecosystem services and human welfare, the relationship between microbial diversity and multiple ecosystem functions and services (that is, multifunctionality) at the global scale has yet to be evaluated. Here we use two independent, large-scale databases with contrasting geographic coverage (from 78 global drylands and from 179 locations across Scotland, respectively), and report that soil microbial diversity positively relates to multifunctionality in terrestrial ecosystems. The direct positive effects of microbial diversity were maintained even when accounting simultaneously for multiple multifunctionality drivers (climate, soil abiotic factors and spatial predictors). Our findings provide empirical evidence that any loss in microbial diversity will likely reduce multifunctionality, negatively impacting the provision of services such as climate regulation, soil fertility and food and fibre production by terrestrial ecosystems.

Is there any attempt to isolate microbial diversity simultaneously from rhizospere, phylloplane, rhizoplane and endophytes ? 

Interesting work...

abstract : Successful invaders must overcome biotic resistance, which is defined as the reduction in invasion success caused by the resident community. Soil microbes are an important source of community resistance to plant invasions, and understanding their role in this process requires urgent investigation. Therefore, three forest communities along successional stages and four exotic invasive plant species were selected to test the role of soil microbes of three forest communities in resisting the exotic invasive plant. Our results showed that soil microbes from a monsoon evergreen broadleaf forest (MEBF) (late-successional stage) had the greatest resistance to the invasive plants. Only the invasive species Ipomoea triloba was not sensitive to the three successional forest soils. Mycorrhizal fungi in early successional forest Pinus massonina forest (PMF) or mid-successional forest pine-broadleaf mixed forest (PBMF) soil promoted the growth of Mikania micrantha and Eupatorium catarium, but mycorrhizal fungi in MEBF soil had no significant effects on their growth. Pathogens plus other non-mycorrhizal microbes in MEBF soil

inhibited the growth of M. micrantha and E. catarium significantly, and only inhibited root growth of E. catarium when compared with those with mycorrhizal fungi addition. The study suggest that soil mycorrhizal fungi of early-mid-successional forests benefit invasive species M. micrantha and E. catarium, while soil pathogens of late-successional forest may play an important role in resisting M. micrantha and

E. catarium. The benefit and resistance of the soil microbes are dependent on invasive species and related to forest succession. The study gives a possible clue to control invasive plants by regulating soil microbes of forest community to resist plant invasion. Source ; Acta Oecologica 81 (2017) 1e9

PDF enclosed for further reading...