Thanks Dr Rao , yes indeed . Based on soil test- crop response studies under grid -based soil fertility valuation , we are  now one step ahead to develop decision support system for soil test -based fertilizer recommendation in citrus . This is how , we  are trying to make soil testing more more  meaningful  in the context of formulating fertilizer doses. Off  course ,  leaf analysis has own precision in such exercises when compared with conventional soil testing program.  

If you mean, by perennial crops, arbustive/tree crops (and not perennial herbaceous plants), plant analysis (single critical ou sufficient values or index values as DRIS or similar) is probably the best approach for nutrient diagnosis.

Once  we get the dataset for leaf analysis /soil analysis, we subject the generated data to various interpretation tools like , DRIS,compositional analysis, critical value concept , sufficiency range , boundary line concept  so on so forth,  to arrive at various diagnostic limits to identify the nutrient  constraints.

I agree to the the opinion of Anoop Kumar that most of the diagnostic methods can be useful for the next season crop (fruit) while addressing the problem immediately is not so useful. When you identify a deficiency and apply the nutrient, a lot of damage has already occurred resulting in decreased fruit yield. 

This is the problem Nazir , that in perennial crops , the lack of response of fertilization  is primarily accounted to erroneous diagnosis of nutrient constraints . And , here comes the definitive role of nutrient diagnostics ( Let it be species/ cultivar  specific) to identify the correct nutrient constraints in a  field/orchard. Role of diagnostics becomes so important that if in a field/orchard , there is an occurrence of N,P , and Zn deficiencies and , through unsuitable diagnostics , we identify  nutrient deficiencies  of N, P, and K  , then , the possible favourable effect of N and P additions  will also be jeopardy or mask the effect of N and P fertilization . This is how , the fertilization response   operates in perennial crops in most of the cases.     

If the diagnostic methods (based on plant analysis) are useful for the next season or for the present season depends on the time response of the laboratory and on other aspect:

the diagnostic must be done in a foresight perspective (hidden symptoms due to light deficiencies or excess); and in this case, the diagnostic may be useful still for the present season;

or are done after visual symptoms, when deficiencies or excess are severe?

 The success of plant analysis  is hugely dependent upon the sampling of  index plant parts , and index plant part sampling comes so late in the season that there is hardly any time left to implement the recommendations of diagnosis in current season. On the other hand , relying on deficiency symptoms ( Mild or severe , sometimes mild deficiency of Fe /Zn hardly interferes with normal functioning of the plant , e.g., sweet orange )  is very risk prone . And that is the reason , identifying nutrient constraints in perennial fruit crops are considered as post-mortem diagnosis.  

Yes, Anoop Kumar views elaborate the problem. Let us hear from other experts.

Yes , let us invite other learned researchers about their candid views on this very important issue  . This would go a long way in offering some concrete solution to such evasive issue.

Dr.Srivastava, how long time it takes the applied nutrients to reach the active roots in  perennial crops like citrus and what proportion of the  current season applied nutrients are utilized in the same season or year ? This will help us to really judge to what extent the foliar diagnosis helps in scheduling fertilizer or manure to perennial crops.

Dr.Srivastava, how long time it takes the applied nutrients to reach the active roots in  perennial crops like citrus and what proportion of the  current season applied nutrients are utilized in the same season or year ? This will help us to really judge to what extent the foliar diagnosis helps in scheduling fertilizer or manure to perennial crops.

Foliar analyses using ICP-MS to measure all the macro and micronutrients.

Dr Rao , I am talking about  the time of taking leaf sample or sampling any other index plant part for tissue analysis -based diagnosis comes so late  in the standing crop season that  a grower has really no time to go for remediation of nutrient deficiencies in the same season . And I am talking this , irrespective of the time taken for different fertilizers to reach to roots . Is there any other possibility to adopt some technique so that nutrient deficiency can be identified  early in the season , and corrected in the same season . in this regard , floral/flower /inflorescence analysis has been advocated very recently , but limited success. 

The season (and organ) for collecting foliar samples depends on the available standard values for result classification.

João Coutinho answer was better.

Infact it is other way round. 

Dr.Srivastava,we can do any  newer aspect for  research purpose  but we can not ignore practical agriculture or horticulture.To my knowledge there is no better tool  than foliar diagnosis of perennial plants at appropriate stage in the  season and index tissue.If right instrument (Dr.Laing) is used  and prompt service is provided Dr.Coutinho),plant analysis provides right data for fertilization,especially for correcting micro nutrient deficiencies through foliar sprays.Progressive farmers may be applying  major nutrients on their own  and their schedules can be corrected during the season  or next season.It is also believed that the the nutrients   take sufficiently long time to reach the active roots in the soil. So one season delay in perennial crops may not be a big  problem.Soil analysis helps  to serve two purposes in tree crops-one during planting and establishing and second for monitoring excess accumulation of nutrients in crops like grapes.This can also be appropriately be used in horticulture.

My response to Joao was somehow incomplete . The time of  sampling of index plant parts  in perennial crops is more dependent on the transition time  between sink-to-source when you consider the relation between available nutrients in soil to accumulation in the developing leaves. This transition period is called sampling time , varying from  3 months after anthesis to as extended  as 8-month  within the cropping season   , depending upon x--factor ( Lets not bring those factors here )  . In a given  situation , the results classification , means various limits of nutrients will depend upon time time of sampling , for example , whether the leaves are from fruiting versus non-fruiting terminal  or position of leaves sampled  on a shoot  . So  the standard values for results classification  are heavily dependent on these factors including the time /season of sampling.  

Same set of leaf analysis data , if subjected to different interpretation tools ( For example,  DRIS versus linear/quadratic regression versus critical limit versus sufficiency range versus boundaryline delineation ...so on ...) , you will get different standards for results classification , irrespective of season of sampling . Yes , your opinion could find some useful  clue that, do we need to implement different standards as per different growth stages of the crop? . Some researchers because of these limitations, advocate using the concept of nutrient logging  vis-a-vis crop ontogeny.  But my question was , what shall we do to make results of leaf analysis implementable  to current season crop? .

 Its so heartening to see ,  discussion building up so interesting . Dr Rao , it is indeed a very intriguing issue as far as practical application  of plant analysis is concerned. Lets separate  the issues like correct sampling , right instrument , delay in analysis and  late delivery of results to growers etc... from on-going discussion. Let me explain to you the problem in right perspective . We collect index leaf samples  in citrus   so  late in the season that crop is left with hardly another 40-50 days for the colour break ( Ideal time of  fruit harvesting ) , and till then there is hardly any fertilizer application remains to be done to that existing crop in the field. Let me know how to make the results of this leaf analysis  results applicable to current season crop . Without ignoring the practical horticulture/agriculture , and  questioning the utility of plant analysis/leaf analysis , let us listen from you , the future course of action  in such situation . But,  let us not refer here about instrument , trained personnel ,time of fertilizer , time taken for fertilizer to reach to roots etc etc. Please also suggest the ways and means to diagnose nutrient deficiency  early in  the season so that the growers get nearly full season for application of corrective  doses of  fertilizers. Can we take the leaf samples , say at fruit set stage or just at the time when fruits are just pea size?. I am really thankful  to all of you  for making this discussion so useful and so interesting .   

I have no first hand knowledge of citrus like you and I can not advise you out rightly But  what I can say you is that there is no harm in utilizing the current season knowledge in the next season,as mentioned  earlier in my reply.One can follow particular   practice for a few seasons  and again go for correction based on plant analysis once again.Real time analysis is neither so easy  nor cost effective.

I have no first hand knowledge of citrus like you and I can not advise you out rightly But  what I can say you is that there is no harm in utilizing the current season knowledge in the next season,as mentioned  earlier in my reply.One can follow particular   practice for a few seasons  and again go for correction based on plant analysis once again.Real time analysis is neither so easy  nor cost effective.

CP: Inductively Coupled Plasma Spectroscopy (ICP) combined with mass spectrometer (ICP-MS)

Benefits system:

1. good sensitivity for different elements

2. The simplicity of the device

3. The concentration of different elements with a solution

4. precision, accuracy, repeatability and good high speed

Let us know , what could be the strategy to identify the nutrient constraints as early as possible in the current season crop?. What is the scope of proximal sensing of nutrient stress since it is non-destructive means of nutrient stress diagnosis.

Anoop Kumar! What will be your plan, can you share please?

A Practical Suggestion: use Mulches around the trees

The use of 100mm thick mulches of organic matter (ideally lignitic material such as the shells of macademia nuts, because these last much longer than cellulosic mulches, which also suck up nitrogen as they compost) will encourage the development of a thick mat of feeder roots under tree crops, to be found at the interface of the soil and the mulch. These are the roots that can take up the foliar sprays best, as the ionic fertilizers wash off the waxy leaves onto the soil surface, and before they can get leached or bound to clay particles. Mulching helps a lot with the uptake of micro-elements such as zinc and iron, which citrus is often deficient in.

Even old newspapers make a good enough mulch to enhance this effect, and you can lift up the newspaper to see the mat of feeder roots developing under it. Nice for measuring this effect also.

I think  number strategies to address this very important issue . First could be to look at other potential index plant parts , for example , inflorescence analysis. If this is fine tuned , probably we will have full growing season to address the remediation of nutrient constraints within the same current season . Another option could be , instead of taking index plant parts , lets use leaf nutrient standards as per critical growth stages viz., fruit set , pea size , marble size , fruit development , maturity , and color break or you can define these stages in terms of days taken from the time anthesis, either way . Third option could be to use nutrient ratio,  instead of individual nutrient concentration , for example , leaf N/K, Ca/Mg, Fe/Mn, K/Ca+ Mg , P/K etc . Such ratios will negate the dilution effect of increasing biomass( Carbohydrate) with expanding time from initial stage of floral primordial formation  to color break.  Use of DRIS is one such success prospects. Off course , these are destructive means of estimating nutrient concentration .

Proximal sensing of nutrient stress has shown good promise, of late , as far as estimating nutrient concentration through non-destructive means is concerned. Spectroscopic methods,  to later convert the results into some kind  of nutrient sensors. Many of the studies have calibrated spectroscopic studies ( Using Vis-NIR spectra) with conventional means of nutrient constraint diagnosis. Further refined such studies into hyper-spectral studies. These will probably act as Early Warning System to diagnose the nutrient stress  right  at the moment, its genesis just takes off .

We have been comprehensively forgetting the promise of the Trunk Nutrition where there are mechanisms through which nutrients can be directly injected into transpiration pull of the plant , irrespective of growth stages. There are some limitations, off course  with perennial  woody plants , but it certainly holds  promise for the better  future .

But right now , the use of leaf analysis complemented by soil analysis plus deficiency symptoms  is surely irreplaceable, with whatever success they have.  I appreciate the efforts of Dr Nazir  and Dr Rao to dig this issue as far as possible. And this is how , the best from any researcher comes out.

Our learned participants to this discussion , if they have any difference of opinion, may please put forth their view. It will surely  pave the way towards refinement of our understanding on this issue.

 I have two unanswered or unclear questions in  provision of good nutrition to orchard crops. First one- position or placement of nutrient on soil and the position of active roots deep  in the soil and  the time taken for actual uptake. The second one- is regarding calibration of soil or plant  test nutrient with amount of nutrient to be applied.If there no calibration  and if nutrients are applied  based on yield or nutrient uptake requirement then  the purpose of precise nutrient estimation at particular growth stage or even real time analysis using spectro-radiometer or remote sensing will not serve any purpose.

 I have two unanswered or unclear questions in  provision of good nutrition to orchard crops. First one- position or placement of nutrient on soil and the position of active roots deep  in the soil and  the time taken for actual uptake. The second one- is regarding calibration of soil or plant  test nutrient with amount of nutrient to be applied.If there no calibration  and if nutrients are applied  based on yield or nutrient uptake requirement then  the purpose of precise nutrient estimation at particular growth stage or even real time analysis using spectro-radiometer or remote sensing will not serve any purpose.

The active root zone of most of the perennial fruit crops  including citrus is 1.0-1.2 times the perimeter of trees on horizontal basis and vertically  roots , especially the feeder roots ( We take the zone of active  feeder root concentration as real root zone  area) up to 40 cm .The tap root citrus is not so deep as plant grows in age , the tap root continues to degenerate  with plant age . This is  regarding your first question . Regarding second question , calibration is done with respect to leaf nutrient  composition versus fruit yield ( No uptake is possible in such situation )  or soil available nutrients versus  fruit yield. We develop the optimum value , and then using these indices , either soil based or leaf  nutrient composition based, the calibrations are undertaken  with amount of fertilizer applied and the magnitude of changes in leaf nutrient value or soil fertility , and then this tri-corner relation  is used for fixing the fertilizer doses. 

In this background only , recently we started  a project on developing spatial variogram of soil fertility and using variable  rate fertilization , based on changes in variogram for soil fertility , we are trying predict the fertilizer requirement as per changes in soil test value,since any soil test value optimum for one yield level , may not be optimum for another higher level , or at a given optimum soil test value for any nutrient , if a fertilizer dose is followed continuously for years  with a much higher yield , it will become sub-optimum  after few years , and so called optimum  fertilizer dose  is to be redefined in the light of higher targeted yield.  

Thank  you for the information .I was under impression that in orchard crops active  roots go up to 60 cm or beyond.I am glad to know that calibration  system is being followed and  new approaches are  coming up.Our recommendation system  in perennial horticulture crops needs revision in light of your comments,if not done already.

Thanks Dr Rao , yes indeed . Based on soil test- crop response studies under grid -based soil fertility valuation , we are  now one step ahead to develop decision support system for soil test -based fertilizer recommendation in citrus . This is how , we  are trying to make soil testing more more  meaningful  in the context of formulating fertilizer doses. Off  course ,  leaf analysis has own precision in such exercises when compared with conventional soil testing program.  

I think, results of proposed investigations may be very good, sharing will help a lot to the other researchers of this field. 

For sure  Dr Nazir , that was the sole objective of digging this issue so deep and across so many researchers , simply to get  variety o researchable  ideas .

Surprisingly  very nice answer and equally very nice links , suggesting your ability to grasp the subject , i compliment you for your understanding on these issues , which are really of very complex nature . Here , i was looking at having some interaction , how could  we ensure the diagnosois  of nutreint constraints as early as possible , so that growers get enough time to respond to outcome of prognostic testing  within the same crop season .. 

Yes, I agree to Dr. Kumar's comments.

Of late methods like proximal sensing , application of geospatial tools , trunk nutrition , have emerged . What kind of promise , they hold in the context of on-going discussion. 

Thanks Abhishek for an excellent feedback. i have gone through this publication . an excellent account of progress made in diagnosis of nutrient constraints has been portrayed. Most important of all is to look at the development of nutrient loss assessment tools through some biological indicators in form of growth of compatible crops.. 

In many perennial fruit crops , the growth of other plants as biological indicators could aid in forecasting the yield of  main crops. Unfortunately , the simulation to other crops is conspicuously missing.  

In fact we need the diagnosis of nutrient constraints on a real time basis directly linking to field conditions. 

Diagnosis of nutrient depend first of all on the metabolism of the plant, on the immediate environment which influence directly the nutrient content. climate change, water supply, organic resources, availability of litter (organic matter) play a direct role in supplying plant into nutrient. for instance, Foliar critical values analysis will allow determination of nutrient content. Also, chemical analysis of each organ like fruit, seed , stem will further the determination of the main center of nutrient absorption and transport. Multivariate and univariate techniques are used also to evaluate plant nutrient content

Adet is quite right.

Interesting response Lucette. Our major limitation is , how to combine the chemical analysis and metabolic analysis of different nutrients and put forth the comprehensive diagnostic value to differentiate different nutrient constraints , depending upon index plant parts...

For the diagnosis of the shortage of perennial plants, the art of dealing with the shortage is for the next season actually and here we have to take into account the role of these elements in the process of flowering because in most crops, especially in fruit crops, the induction and initiation of flowers takes place in the summer and autumn of the previous season, we have to address the shortage in the current season To show results in the following season.

Well said Dr Ali. Infact this is the major limitation with the current state of art of diagnosis of nutrient constraints in perennial crops..