Dr Srivastava, I agree with you. Lets listen from our colleagues on such a burning issue.

Dear Anoop Kumar Srivastava, 

Micronutrients - chemical elements needed for the occurrence of vital processes in living organisms, they contain very small amounts (less than 0.001%). Despite the negligible content they are essential to plants.

Trace elements are active substance micronutrients.

Called micronutrients because they are needed only in minuscule amounts, these substances are the “magic wands” that enable the body to produce enzymes, hormones and other substances essential for proper growth and development. As tiny as the amounts are, however, the consequences of their absence are severe. Iodine, vitamin A and iron are most important in global public health terms; their lack represents a major threat to the health and development of populations the world over, particularly children and pregnant women in low-income countries.

Trace elements are different in their physical and chemical properties. Among them there are metals (zinc, copper, manganese, cobalt, vanadium, molybdenum), nonmetals (boron), halogens (iodine).

Best regards, Shafagat

Which of the micronutrients contributes maximum towards residual fraction on two contrasting soil types acid soils against alkaline soils against calcareous soils.

Dear colleagues, could it be that it's because our plants need these nutrients in such small quantities that deficiency is rare, and so we talk mainly about N, P, and K?

"Deficiency of micro-nutrients is not common for field and vegetable crops grown on soils with pH

Miranda in fact it is otherwise. Micronutrients deficiency is most pronounced in all types of soils and crops with few exceptions. Most important is to look at their impact. World agriculture is facing acute shortage of micronutrient.

Dear Sikha, you may be right when we consider that we are taking the nutrients out of the soil (with the vegetables that I have been planting).  But perhaps organic manure returns these back to the soil.  Here in my state, some farmers use chicken dung. This is part of my lab garden.  You will recognize some of our plants.  Some are for food, some are for photosynthesis pigment experiments etc...

Miranda, we are talking about the commercial fields whether these are vegetables, fruits or cereals where micronutrients use is a common practice. we are not talking about homestead gardens or lab gardens where the cultivation is just for domestic use. Use of organic manures cant be adopted on a large scale with exclusive use of manures.

Micronutrients are essential for plants, so if the soil does not need to the addition of these nutrients plants can absorb it without any problems. But if  soil has a problem such as pH>7, lack of soil organic matter??? the simple answer, the availability of these nutrients will be restricted so with different plants the deficiency symptoms will appear on the plant. Maybe plants can adapt with  this problem or not.   An example, Fe is important for citrus trees, with adding Fe to trees the leave's  chlorophyll, nitrogen and  potassium content will increase. Area and length of leaves will increase also. 

Another problem is the relationship between the macro and micronutrients in soil. The excess of the addition of N will decrease the absorption of Cu and B. Phosphorus can lead to the decline of absorption of Cu, Zn, Fe. Potassium increases the Fe and Mn absorption by plants but decreases the absorption of B. If calcium is present in soil with large quantity it will decrease Zn, B, Fe and Mn. 

Dear Colleagues

As Doctor Srivastava ably points out the role of micronutrients is very compelling based on economics that minor additons can achieve major effects.

I believe the diagnostic tool application is most limiting our advances in this field.

Are we routinely and economically able to have the complete soil and plant analysis available plus an interpretative recommendation which the farmer can find useful and applicable?

I think the answer is most not so. We rarely have the right informational system and their outputs optimized to eliminate these issues that are outstanding.

The strategy of optimizing micronutrients needs to include the remediation of soil pH. These constraints with about one third of our whole soil being acid infertile and another one third having issues with alkalinity and salts and in both of these conditions micronutrient issues abound.

Cause we do not attack the roots of the problems but instead we concentrate only on the symptoms. If the cause is soil reaction the emphasis on foliar seed and soil amendment is at best a partial solution. .

I further believe that over 80% of the world soils are not optimized for soil organic matter. When lack of micronutrient levels are combined with pH remediation  and soil organic matter adjustment I believe we have a powerful combination that will resolve these micronutrients issues without looking only at short term addressing of acute symptoms. In the mean time until we get the twin roots soil pH and organic matter addressed we need the strategies of targeted addition which treat the symptoms rather than the root cause as interim actions.

It is interesting to see that the most fertile soils in the World come about where the annual precipitation and evaporation rates are about the same degree. This confluence gives a equilibrium where the soil system does not overly lose or gain salts. Indeed this suggests are problems and issues are related to leaky systems which do not have a closed nature to them.

We need to take the issues of micronutrients using a big picture outlook looking at root causes rather than just the symptoms of disbalance for this reason systems thinking and long term evaluation will come to the forefront for real soil lutions.

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Anoop Kumar Srivastava to you

18 hours ago

Your response in this matter will be highly appreciated friends

9

Why do we hardly talk about residual effect of micronutrients ?

The role of micronutrients in sustaining agriculture is well documented.The requirements for different micronutrients ( Fe, Mn, Zn , Mo, B, Cu ) are so small , but these micronutrients have the ability to mask the potential response of different macronutrients (N,P,K) on growth , yield , quality and post-harvest life as well. Although , annual application of micronutrients is small , but major proportion of applied is diverted towards immobilised fraction , which expends consistently with each annual application . In this background, i propose following questions for your kind response dear friends :

* Which of the micronutrients is diverted least or most towards immobilised form of micronutrients ?

* What kind of diagnostic tools do we have to keep possible check on expansion of immobilised fraction in soil ?

* How does cropping sequence affect the size of immobilised pool of micronutrients?

* What is the most effective strategy to mobilise this fraction towards plant available pool of micronutrients ?

Regards

[more]

Noha Mahgoub

Micronutrients are essential for plants, so if the soil does not need to the addition of these nutrients plants can absorb it without any problems. But if soil has a problem such as pH>7, lack of soil organic matter??? the simple answer, the availability of these nutrients will be restricted so with different plants the deficiency symptoms will appear on the plant. Maybe plants can adapt with this problem or not. An example, Fe is important for citrus trees, with adding Fe to trees the leave's chlorophyll, nitrogen and potassium content will increase. Area and length of leaves will increase also.

Another problem is the relationship between the macro and micronutrients in soil. The excess of the addition of N will decrease the absorption of Cu and B. Phosphorus can lead to the decline of absorption of Cu, Zn, Fe. Potassium increases the Fe and Mn absorption by plants but decreases the absorption of B. If calcium is present in soil with large quantity it will decrease Zn, B, Fe and Mn.

[more]

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Paul Reed Hepperly

13 hours ago

Dear Colleagues

As Doctor Srivastava ably points out the role of micronutrients is very compelling based on economics that minor additons can achieve major effects.

I believe the diagnostic tool applications are limiting our advances in this field.

Are we routinely and economically able to have the complete analysis and a recommendation which the farmer can find useful?

I think the answer is rarely in our informational system and their outputs optimized.

The strategy of optimizing micronutrients needs to include the remediation of soil pH constraints with about one third of our whole soil being acid infertile and another one third having issues with alkalinity and salts.

Cause we attack the roots of the problems with concentrating only on the symptoms? I do not think so.

I further believe that over 80% of the world soils are not optimized for soil organic matter. When these two major players pH and soil organic matter are taken care of the issues with micronutrients will be much less of the issue. In the mean time until we get the twin roots of the issues we need the strategies of targeted addition which treat the symptoms rather than the root cause.

It is interesting to see that the most fertile soils in the World come about where the annual precipitation and evaporation rates are about the same degree. This confluence gives a equilibrium where the soil system does not overly lose or gain salts.

We need to take the issues of micronutrients using a big picture outlook looking at root causes rather than just the symptoms of disbalance for this reason systems thinking and long term evaluation will come to the forefront for real soil lutions.

Anoop Kumar Srivastava to you

6 minutes ago

Dr Hepperly , you have raised very pertinent points , but unfortunately, your response is not uploaded in the question . Can you please , load it again to initiate the discussion . Thanks.

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Dr deka thanks , your concern is infact everyones concern on this matter.

Dr Miranda , suboptimum micronutrients supply in recent years has been the talk of every researcher. what could be done to ensure optimum supply of micronutrients . unfortunately , keeping soil pH always in the vicinity of 7.0 is not possible. Dr Sawicka , you got it right , we have the residual effect of nutrients like nitrogen , phosphorous, but why don't we discuss about the residual effect of micronutrients , simply because , they are applied in small quantity ,and so their requirement are so small ?  . Dr Noha , I agree with you there has to be balance between fertilization of macronutrients and micronutrients , but unfortunately , this is  not the case. Infact , if you omit the micronutrients application , you will not be in a position to harness the effects of applied macronutrients. Hope , we will get some further feedbacks from our colleagues on these issues , which I flagged off?.

Dr Hepperly , my point of view was , simply on the lines of mobilizing the insoluble fraction of micronutrients that exists in soil , irrespective of crop , annual or perennial in nature. On one hand , I agree , most of the micronutrients in perennial crops are used as  foliar spray , with limited application of micronutrients injected into the soil . But in annual crops , soil application of micronutrients is still the choicest way of fertilization .

A very nice question as usual. As mentioned above, the amount of micro-nutrients applied to plants is  very small, mostly in few grams per hectare. That is why they are called micro-nutrients. They are applied as folliar spray because of their quantity, or as soil when they are provided with major nutrients. For example, zinc and copper are formulated with NPK and sulfur, and direct soil application is common. Folliar application is more efficient and fast acting than soil application.

Therefore, the residual effects of micro-nutrients on plants appears very low both for annual and perennial crops, unless there is high applications of organic fertilizers, such as compost or manure. However, soil type associated toxicity problem may arise from some micro-nutrients such as aluminum, iron and manganese, which is common in acidic soils. In Ferralsols or Oxisols of the humid tropics, soil pH is very low due to the depletion of major cations, and oxides and hydroxides of aluminum and iron remain on the soil particle as a resistant materials. Native labile or applied phosphorus is fixed by these materials and form a complex of Al-or Fe-phosphate and can be available to plants until these materials are saturated by excess application or liming.  In this case Al can be taken in excess and can be toxic to plants. In fact, the availability of Al is important for the quality of tea plants. On the other hand, Fe and Al may be deficient in high pH or calcareous soils. Essential elements such as boron and molybdenum may be deficient in acid soils. Thus, discussing this issue in terms of balanced nutrient application may be more relevant. Because the application of certain major elements in excess can be the cause of the depletion of other essential elements.           

Excellent response  Getachew , so impressed with your comprehensive arguments on the issue. There is absolutely no two opinions about the amount of micronutrients being applied annually  to field crops and perennial fruit crops . Sometimes , toxicity of Fe and Al acts  a blessing in disguise. For example , in some of the tea  growing areas , we observed that amount organic carbon is 2-3% while Bray-P is somewhere 4-8 mg/kg , but still good flavored tea was experienced , simply because of the  weaker adsorption of phosphate on humates/fulvates than Al oxides as opposed to our conventional understanding  , immobilization of P by Al-oxides is stronger than humates/fulvates in such acid soils. And this adsorbed phosphorous during the peak vegetative flush is desorbed  into the active pool of soil P , thereby , maintaining the optimum P-supply in soil coupled with required low temperature .  My second point of contention is in most of the arid/sub- tropical soils , micronutrients like Fe, Mn, Zn , and B , Mo to lesser extent remain confined  in residual fraction , whose legacy continues from  crop season to another crop season, irrespective of nature and properties of different soil types . How can we dislodge this fraction( otherwise totally inactive fraction without any use to plant nutrition) , much to the benefit of the crop yield and quality ? . Hope to get back your another excellent response. Regards  

What are the well established strategies to mobilise the calcareousness induced iron deficiency in calcareous soils.

That's what I flagged off earlier in the discussion Dr Deka  . A major proportion of soil pool of micronutrients are confined to residual fraction , whose residual effect is still untapped or we have yet not seriously attempted to transfer this pool towards the active nutrient pool of the soil . And this fraction in calcareous soils would be much larger because  of the much stronger sink that calcite of different sizes acts as sink  for nutrients like iron .  Shall we adopt to the standard strategies of calcareous soil management ?.

Here is some literature about the management of lime induced iron chlorosis  with regard  to different fruit crops , in addition to literature on management of calcareous soils including the use of siderophores producing concepts as some of the latest concepts.

Interesting Manuel , real out of box thinking , appreciate it .

I am enclosing some of the literature to discussing about the residual effects of nutrients like Fe and Mn . Interestingly , where organic manures are practiced  , the residual effects of Fe , Mn, Zn are carried to many seasons , depending upon the yield levels obtained ( ftp://ftp.fao.org/agl/ahll/dos/fpnb5.pdf) . In this context Getachew is dead right .This is where perhaps organic manures fit so well in the context of providing the holistic plant nutrition . However , it remains to be seen how the residual effects of other micronutrients behave in  soils of varying mineralogy.  

As far as soil application is concerned Cu is the micronutrient with the largest residual effect: at an average uptake of 50g/ha a single application of 5kg/ha Cu in what form ever (mostly elemental/oxide mixtures) supplies a field for several decades. We know this from the post war times in Germany where virgin land (usually high in OM) were brought into production, showed severe Cu deficiency especially in oats and barley ("called Heidemoorkrankheit" translated "heathen-moor-disease") and application of Cu-slags from Cu smelters was recommended widely for remediation.

Mn is not a question of soil reserves but of pH maintained mobility: you may expect Mn deficiency when your pH (in KCL) raises above 6.6, but then soil application is also without any effect and you are stuck to foliar application.

B is a typical deficiency factor on light soils in humid climates due its prone to leaching. Soil application is efficient, but any residual effect mostly unwanted, because in a rotation monocots are very sensitive to B toxicity, so the method of choice here is foliar application to B needing crops like Beta or Brassica species.

Zn may be deficient in a number of cases, but to my opinion its general extend is far to exaggerated (I wrote about biased information in this context elsewhere on RG). The good news is that Zn is very seldom toxic to plants, but that does not justify uncontrolled application with fertilizers, especially as there is coming plenty of Zn through fertilizers prepared from municipal wastes.

Fe is like Mn also known to be primarily a problem of mobility, so any effects through soil application initial or residual is close to zero, which brings foliar application again in the first place of countermeasures.

Mo deficiency is very rare and partly due to  low soil reserves or mobility. as its true for any of the other micronutrients: NO ACTION UNTIL A PROPER DIAGNOSIS HAS VERIFIED A NEED!

For Mn soil analysis is more or less inefficient (but have a try with our  Method; see contributions), for Cu and Zn WESTERHOFF (0.43m HNO3) is well proven on non calcareous soils, otherwise DTPA according to Lindsay and Norwell, for B hot water extraction according to Boenig and Heigener) are very well calibrated.

When I worked with scientists at the Illinois Natural History Survey Dr. Eugene Himelick was concerned with iron chlorosis of the shade trees using as street shade. The use of pin oak which is a forest species from acid soils were quite ssusceptible and a very good alkaline carbonate indicator. Much of issues were related in side walk lime and depsoits of construction wastes.

 We would inject iron chelate and resolve the problem something very difficult in a field situation.

The foliar applications of micronutrients such as Iron and Manganese does not lead to optimized micronutrient in the root zones.

As Ewald has suggested the problem is soil mobility not not reserves and this is mostly governed by genotype selections and practices to modify the soil pH at least locally. We need much more consciousness on correcting these issues from the soil up and pH adjustment is often underestimated and overlooked. The use of biomarker species indicate the issues which is usually quite locallized. The species hydrangea will show soil areas which in the same plant root ball are alkaline and others areas in the same plant that are acid. This can be utilized for an evening out of the issues by applying Sulfur in the alkaline zones and lime in the acid areas. 

Can anyone supplement further information about the duration in terms of number of seasons, the residual supply of micronutrients from different manures continues. Manures like poultry manures, vermicompost  contain so much of micronutrients they must getting lodged into the residual fraction of the soil only.

Well said by  Ewald , different micronutrients have different behavioral chemistry . Lets take an example of nutrients like Cu and Zn ( I agree  with   pH -dependent availability of nutrients like Fe and Mn ) . A major proportion  of these  applied  nutrients is diverted towards those fractions, so difficult to drag them out into the readily available fractions . Is it the , the stronger intervention of adjusted cropping system is to be bought in or soil amendments hold better choice?

Paul , very effectively put  forward your  arguments as usual  . But despite foliar sprays of nutrients like Fe, Mn  etc , do you feel the plant rhizosphere is still in  short supply of such nutrients , and eventually appearing such symptoms more than often compared to those soil conditions rated optimum supply. Very often soils have such a strong buffering capacity that inflicting such change sin soil pH becomes impractical ?. Under such conditions , do you feel re-adjustment in cropping sequence would be the  choicest alternative?

Dr Deka , its a good point , you have raised . When we use organic manures , our major concentration remains to see , how long we can cut the dose on nitrogen , phosphorous and potassium to some extent , but we hardly look at the residual effect of nutrients like Fe, Mn, Zn . Simply , soil -test based recommendation we frequently undertake  to get guidance for future course of fertilization to be followed in a given field.  I will appreciate , if any one of us  can provide further feedback on this very important issue.  

Most micronutrients are resolved when targets for soil organic matter are optimized. Original lands put into cultivation had in excess of 5% soil organic matter many of our soils now are in the 1 to 2% level which is too low for optimization in a high yield environment. The targeted increase of soil organic matter would resolve many of these issues. I agree with Anoop that soil provision is better than strictly using the foliar route. The advantage of soil organic matter approach is that water is our biggest agricultural limitation and soil organic matter is our biggest water sponge. No nutrient is absorbed by plants except through the agency of water. 

Well articulated Paul , no doubt . Legacy of  applied micronutrient s diverting towards the residual fraction of nutrient needs to be transformed through rhizosphere -based treatments , adjustment in soil ph coupled with PGPRs , AMs and suitable amendments could jointly frame a very good option in this matter to  be resolved more regular than often .   

In most cases if not all cases the complex issues such as nutrition and greenhouse gases are not going to addressed by a single silver bullet practices. .

In relation to these issues the systematic use of many practices which have incremental effects and/or synergistic effects are the need. Narrow technology approaches are not the solution of most of big issues but are useful in the problem solving array. Narrow approaches can be part of the issues and challenges we face in our society and our businesses and educational systems. We need to grow in systematic knowledge and long term interdisciplinary teams.

In integrated crop protection this starts with the idea that no single practice will do and then identifying the small practices that when stacked together give comprehensive addressing of the core issues. These good practices which of themselves are not sufficient are called little hammers and together they form a sledge hammer which can destroy the principle constraint.

This type of integration of practices should be part and parcel of our approach to complicated issues. Use practices as tools in a tool box and then integrate them systematically to find integrated solutions.

This very important concept is not over glorify technological issues but rather join together with practical farmers in the real world outside the ivory towers. The combination of the best science and traditional wisdom can be applied and benefits society our humbleness service orientation is needed as acientists and academics. 

Dr Hepperly, is there any serious attempt to trace the solubilization of micronutrients that have accumulated in soils in residual fraction something like P- solubulisation ?

The mycorrhiza researchers have done most of the serious work in this area using the mobilizing of Zinc and Copper in their analysis. The mycorrhizal mycelium network can extend some 10 cm from the plant host root and the increase in surface area of the of hundred to thousands of times the surface are the symbiotic network can contact. The interesting thing I see is that the network displays some sought of almost intelligence as the activity is response to actual need by the plant and its host.  The fulvic and humic acid fractions of organic matter are notable in their capacity to mobilize the insoluble fractions of trace minerals and Phosphorus from mineral soil fractions and are used for aiding the use of micronutrients in plant applications such as foliar fertilization. My friends and teachers who worked on these areas are now retired and included Frank Stevenson deceased at University of Illinois and Dr. Rhodes retired who was Professor in mycorrhizae at Ohio State University.  There is continuing need to disclose these mechanisms I believe. The Indian mycorrhizal fungi Piriformaspora indica is probably the best model system as the mycorrhizal component is easily cultured in the laboratory. Early mycorrhizal work was complicated by the inability to culture the myco component without its host plant. In terms of mycorrhizae they seem to able to help in toxic situation and deficiency situations which why it is suggested their system action is almost intelligent. 

Well said Paul . Some of our old  well established practices have taken a back stage , amidst newer developments  . i do not see,  now a days a stronger  intervention of cover crops/ green manuring  . necessity of maintaining   a critical level of organic matter in the soil  finding difficult  , in the light of  lesser and lesser application of organic manures ..much in the favour of inorganic fertilizers . In this  current context ,  we need renewed efforts to invest upon the role of microbial synergism -plant  syndicate , including the role of AMs, which could well have the utility in overall soil fertility , not the phosphorous alone. unfortunately , application of AMs not finding so much of  filed  popularity , as much  it deserves..?

My question is addressed to Dr Paul, Dr Srivastava and other colleagues. How do you see the role of phytosiderophores in micro-nutrient mobilization as a function of microbes.  

Dear Parmeshwar Shirgure,

The simple answer is yes.

In an ecological sense we as humans, the animals we tend and the microbes that recycle they all dependent not on ourselves per se but  on plants as primary producers. Anthropocentric views are just not sustainable we cannot view are selves as sources of what has come about. 

The animal and microbial communities are the conveyors of the movement of nutrient back to the plant from the soil and from the air to soil.

Doctor Dodge a initiator of the the studies of fungal genetics from bread mold said it this way "When the last plant and animal dies there will be a fungus to decay them".

Rather than looking at kingdoms of organisms as separate they are all part of a single organism following a Gaia type of hypothesis. 

Plant animals and microbes are all working and breathing together. When we see the microbes as enemy we over prescribe antibiotics and our digestion fails causing big problems and issues. While no doubt some microbes are troublesome the fact remains that the vast majority are not and many are highly beneficial.

Although we by tradition study botany or zoology the microbes they are always there interacting with us largely in highly beneficial ways but mostly unseen by us.

Since plants serve as global solar collectors they are the givers and providers for life on Earth and as in the case of Rhizobia and mycorrhizae they work to reach unto the plant kingdom to help the team expand the Kingdom harvesting the air an dd and rock material of the soil itself.

The intelligence of such an intricate arrangement in of itself would defy probability and would be a prime motivator of considering existence of Higher Power and Design. I for one cannot fathom such arrangements coming about from chaos and random events. 

I certainly can believe that all this arrangement is not my doing and not by random. So then what?

Agricultural applications[edit]

Poaceae (grasses) including agriculturally important species such as barley and wheat are able to efficiently sequester iron by releasing phytosiderophores via their root into the surrounding soil rhizosphere.[19] Chemical compounds produced by microorganisms in the rhizosphere can also increase the availability and uptake of iron. Plants such as oats are able to assimilate iron via these microbial siderophores. It has been demonstrated that plants are able to use the hydroxamate-type siderophores ferrichrome, rodotorulic acid and ferrioxamine B; the catechol-type siderophores, agrobactin; and the mixed ligand catechol-hydroxamate-hydroxy acid siderophores biosynthesized by saprophytic root-colonizing bacteria. All of these compounds are produced by rhizospheric bacterial strains, which have simple nutritional requirements, and are found in nature in soils, foliage, fresh water, sediments, and seawater.[42]

Fluorescent pseudomonads have been recognized as biocontrol agents against certain soil-borne plant pathogens. They produce yellow-green pigments (pyoverdines) which fluoresce under UV light and function as siderophores. They deprive pathogens of the iron required for their growth and pathogenesis.[43]

Dr Paul and other colleagues, can we synthesize phytosiderophores and use it as artificial inoculants in soil or foliar spray...? Just an imagination...?

I do not think we can synthesize phytosiderophores synonymous to natural phytosiderophores. 

The residual effects of soil oligoelements are  mainly depended on soil characteristics and cultivation practices. 

In relation to the question if we can artificially  synthesize phytosiderphores which are identifcal to natural plant phytosiderophores the answer is probably yes.

The natural plant siderophore such as an example Citric acid is found naturally in oranges and citrus but also is synthesized artificially and used as food processing ingredient giving acid reaction and distinct flavor.

When we have natural source the more raw products the mixture of ingredients can give subtle differences.

For instance vanillin is produced artifically but it is not synonymous for a expert taster or gourmet to natural vanilla bean extracts or powders.

Currently EDTA is the major chelator for iron mobilization and it is called Sequestrene in North American market. This would not be considered an organic or natural product.

Insoluble mineral Iron can be mobilized by fulvic and humic acid products and finely ground iron rich mineral would be solubilized with these materials.

Taking that approach Fulvic Acid solution would be best choice as the product is naturally acid soluble and iron issues are particularly always a consequent of soil alkalinity and excessive carbonate and the amounts of iron in soil without that constraint is not generally problematic. 

When soils which are alkaline are acidified they generally alleviate not only issues with Iron but also many others such as Zinc and Manganese. 

I believe our first constraint for balancing our nutrition is getting soil pH right for our production goals. 

One of the reasons Pigeon Pea can grow so well over both acid and alkaline conditions is probably related to its ability to produce organic acids which broaden the plant adaptability in that case psycidic acid has been suggested.  

Thanks Nikolaos and Paul for your thoughtful responses . I do agree with you Paul, you can synthesize plant siderphores  for better rhizosphere environment  vis-avis  iron nutrtion. Siderophores (from the Greek: “iron carriers”) are defined as relatively low molecular weight, ferric ion specific chelating agents elaborated by bacteria and fungi growing under low iron stress. The role of these compounds is to scavenge iron from the environment and to make the mineral, which is almost always essential, available to the microbial cell. Research in this field began about five decades ago, and interest in it has accrued with the realization that most aerobic and facultative anaerobic microorganisms synthesize at least one siderophore. Siderophores have been related to virulence mechanisms in microorganisms pathogenic to both animals and plants. In addition, they have clinical applications and are possibly important in agriculture.  

Another point , you have picked up Paul , is the soil pH. most of the soils have excellent buffering capacity around neutrality , and it is not always possible to keep soil pH within those desired range , simply because of soil mineralogy does not permit to attain that pH. for example basalt-derived parent material under under humid regions develop always soil pH ranging from 7.2-8.0 , still we hardly see any distinctive nutrient deficiencies. On the other hand ,  soils derived from granite-gneiss parent material under same humid regions  produce pH somewhere  as low as 5.1 to as high as 6.1 only . /and , i consider both the types of soils having very strong  natural buffering capacity  , much to the inconvenience of the plant nutrition to buffer soil pH around neutrality ...

Some thoughts in your response... 

Dr Hepperly and other colleagues, how do you differentiate between natural chelates and siderophores ? Do they compliment each other ? 

Inputs can be like drugs at first they work optimally and then as the body become habituated to them their activity and benefit diminish.

In a conventional sense it has been said for example Nitrogen is Nitrogen this is complete over simplification and not true in any deep sense.

If we get our Nitrogen for instance for biology through Nitrogen fixation in plants we avoid most economic, energetic and environmental issues related to Bosch Haber process to produce ammonia and these are enormous.

Natural mechanisms based on biology I would argue have better overall effect than synthetic chemical approaches.generally.   

When we talk about micronutrients the potential for these alterations are less than the same approach for  Nitrogen. This is because the amounts being needed or applied is small. If Iron is added foliarly or injected into a tree trunk the cost and impact to the environment of the input is probably minor.

The relative high positive impact from small quantitites make that a wonderful area of cost effective non disrupting opportunity to increase our agricultural capacity. In fact micronutrient deficiencies are extremely common especially in developing World environments but also in developed economies. 

My own philosophy is the our soil is the society bottom line and when we improve it all the issues are lessened. I support the use of regenerative practices which by it name are designed and focused at giving life and energy back to the field is way to prosper our health and society.

The use of systematical agricultural practice which favors biology rather than a synthetic chemical input approach is what from my own experience does this well. Our biggest input needs to be our own ingenuity with an eye on maximizing the natural available life forces. 

Field crops are known to take up only 0.3% to 3.5% of the annually applied fertilizer Zn. Consequently, fertilizer Zn accumulates in the soil. Because of its low mobility in the soil, positive effect of applied Zn on subsequent crops in the rotation may last over variable period (Brennan 2001).

One application of 7.5 kg Zn/ha was found adequate for  optimizing two cycles of the cotton-wheat production system in a silty loam, alkali soil of pH 8.1 (Typic Haplocambid) containing 0.78% OC, 5.6% CaCO3 and 0.45 mg/kg DTPA-Zn. For detailed information on the field experiment, you may read the following article:

M. Abid et al. (2013) Residual and cumulative effect of fertilizer zinc applied in wheat-cotton production system in an irrigated aridisol. Plant Soil Environ. 59(11): 505-510.

For easy access, I attach herewith PDF file of the article.

Dr. Kundu's information is very important in the budgeting of application of micronutrients to plants.  Considering which application method is most appropriate for efficient utilization of micronutrients is also very useful, i.e. soil or foliar application. Crop and soil types are also very important (e.g. annual and perennial crops). Besides soil and plant test is very important to optimize the efficiency of micronutrients.

very interesting discussion, this time I will follow the researchers discussion. thank you prof.

Thanks my all the three learned colleagues , Dr Kundu , Dr Getachew and Dr Hussain . Zinc is the most ominous nutrient , whose deficiency is  prevalent , equally on acid as well as alkaine /calcareous/salt affected soils. Incidently , our crops edible parts are also equally poor sink with regard to Zn .And , above all our failures to replenish Zn export from our soils , neither we have that full proof methodology tom ensure better Zn nutrition , besides the nutritionally healthy food.  Let me cite some excerpts from an excellent paper of Jones et al published in J. Applied. Ecol. ..:

Nutrient export from land, with no capacity to replenish those nutrients, represents a long-term stripping of soil stocks, exposing developing countries to significant longterm risk of soil productive failure (Stoorvogel & Smaling 1990), and the associated health consequences. For example, approximately two billion people in the world are thought to suffer from at least one of the many forms of micronutrient malnutrition (WHO 2007; FAO 2009). Whilst such deficiencies tend to impact people in developing countries (Zhao & Shewry 2011), for example zinc (Zn) in India, there are also important micronutrient shortages such as selenium (Se) in developed countries (Rayman 2000). The socio-economic consequences of these deficiencies are substantial and widespread (WHO 2002; The World Bank 2006). Combating micronutrient deficiencies is considered by many to be a cost-effective intervention as measured by the Disability-Adjusted Life Years (DALY) averted and costs per DALY averted (Meenakshi et al. 2010). For instance, estimated annual disease burden of Zn deficiency in India is 2.8 million DALY lost, of which 2.7 million are due to mortality and 140 000 to morbidity, the majority of which are infants (Stein et al. 2007). Providing sufficient nutrients to the world’s population is contingent upon national agricultural systems functioning efficiently.

Excellent stuff...

We can mobilise the unused portion of micro-nutrients by using nutrient efficient crops are by adding good amount of organic manures. 

Dear Colleagues, The Role of micronutrients can be dramatic. As Parameshwar Shirgure aptly injects organic amendments can be excellent sources of micronutrients. I believe that if the focus is on soil organic matter many of the micro nutrients issues are avoided. The issues of micronutrients can often be traced to depleted state of the soil. The soil is depleted based on losses incurred over many ages. These materials are lost to the seas through erosion and leaching. The use of kelp brown sea weeds is rich in micro nutrients and has excellent resource for the mobilization of these based on humic like substances from these marine resources. As agriculturalist the completing of the nutrient cycle or circle is very important unless the complete nutritional base is provided the productivity and health of plants, animals and humans will suffer. Some thoughts, P

Thanks Paul , for placing the good argument about the utility of organic amendments in combating the multiple micronutrient constraints on one hand , and mobilising the residual fraction of soil Fe/Mn/Zn through a number of processes like dissolution , chelation , complexation  etc  to maintain th intensity factor of these micronutrients in the soil at almost regular pace in tune with crop requirement ...

Friends, let us add some discussion on how to to utilize the residual fraction of micro-nutrients which is the most predominant fraction of the soil micro-nutrients. 

Friends I want to invite your opinion in which case there will be greater residual effect of micro-nutrients when we compare fertigation against foliar application. 

Let me add another response. We need to find out some effective ways of mobilizing residual fraction of different soil micronutrients using multiple microbial inoculation methods. 

Thats the main issue , my dear friend , when we look at the efficiency of different micronutrients , its hardly 10%...