The problem is that the relationship between plant availability and the test results are plant species and soil specific. Thus all the tests we do will always have limitations and never provide a 100% certain answer. Even pot trials are only approximations of nature.

However with the benefit of experience with the specific plant in the specific circumstances at the time we can get valuable information for agronomic and ecological studies.

In  my opinion there is no single answer to your question.

You will need the Saturated Media Extract that is also used to determine accurate pH and E.C.. You can use the extract to run a test for all nutrients of interest.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CCQQFjAAahUKEwjMq_Tdie3HAhWGNYgKHX-7B3w&url=http%3A%2F%2Fwww.clemson.edu%2Fsera6%2FGreenhouse%2520Media_first%2520draft.doc&usg=AFQjCNFLhmhSnuKWxP0FCJo_xm2OaPk29g&sig2=sNWKA6doVVvYXHKdosovHg

I wish to clarify that the new procedure can be for a few important nutrients and it need not be for all essential elements.I wish to know new ideas and approaches if available.

We all understand that there are many factors which control availability of nutrients to plants in soils. Soil environment, soil physical properties, soil composition, etc. Therefore , it always demand soil specific and crop specific recommendations for nutrient applications. The best method of analyses or extractants should be such which present best nutrient availibility index or correlation  for a particulat soil and crop. Dr. Hani Antoun gave a good suggestion for leaf/ tissue analysis to interpret nutrient demand of a crop in a particular soil.

There are existing recommendations for various soils like acedic ; alkaline soils and different nutrients for extractants and soil analysis methods . Therese offer , mostly acceptable solutions as these are developed after studying soil extract and plant nutrient availability correlations. Generally water soluble , exchangeabe nutrient extractants and nutrient complexing agents are advised for soil nutrients extractions and analyses. and soil test crop correaltions are developed for such recoomendation for particular soils. Where such information is not available , better soil test crop correlation be studied / developed for arriving at final conclusion..

The best way it determine plant available nutrients in the soil is using a soil test that has been calibrated for plant response or uptake for the specific crop(s) of interest.  There are a number of tests in the literature. Some work better that others in specific climates.  The attached publication describes the standard methods used in the North Central US which are calibrated with numerous crops.  The Soil and Plant Analysis Council and the International Plant Nutrition Institute should also have resources that can help you.

http://extension.missouri.edu/publications/DisplayPub.aspx?P=sb1001

This question has been exercising the minds of scientists for almost a century, and to be honest, for the large amount of effort  spent the progress in predicting fertiliser requirements, even for elements such as N, P and K,  has been limited to those areas where intensive test calibration has been conducted.  Everywhere else monitoring and plant analysis are the standard.

The only 'new' approach I'm aware of relies on  measuring the rate of diffusion into an 'infinite' sink.  This mimics the main processes in nutrient runoff and is a useful research tool.

However, other major processes occur in the rhizosphere, e.g. high CO2 concentrations and redox reactions.  These processes considerably influence nutrient supply to roots in most soils. 

The intellectual challenge is to mimic more of the key rhizosphere processes and find out what proportion of nutrient uptake that predicts.  Then one may be able to logically approach the development of practical, universal soil tests on disturbed samples in the lab. 

There is no guarantee that superior knowledge will translate into something superior to the current 'cocktail' extraction/ICP methods, but that is the nature of research.   The devil in me says, why not simply ask the plant what nutrient difficulties it is experiencing and rely on local experience for fertiliser rates? 

 Dear Dr .Milham,in five paragraphs  you have very nicely summarized the  basic ideas behind the soil test procedures and use of the procedures for recommending fertilizers .Even though most of the soil  extractants were more than half a century old, with good calibration in some soil- crop situations, they are doing very well.It is now well established that organic acids like citric acid,lactic acid acetic acid and malic acid play a great role in solubilization of plant nutrients like P and micronutrients in rhizosphere, exchange  and chelation of micronutrients.Originally Dyer(1894)developed the 1% citric acid method over a century back for extraction of  probable available phosphorus in soil.After exactly a century later G.R Thompson(1995) solved some of the analytical problems in the method.The importance of CO2 in nutrient solubilzation was also realized in early part of 20th century.Puri  and Asghar(1936) passed carbon dioxide through a 2%aqueous soil suspension for 15 minutes and determined phosphorus in the titrate. Even cation/anion resin membrane/bead based methods are half a century old.These resins serve as sinks for available nutrients in soil and resin sorbed nutrients can be replaced by some dilute acid and can be estimated.Some companies came up with some resin based portable probes.With all the developments still our progress is limited extent. As  mentioned in your last paragraph for some crops like hybrid maize at high yield levels, the plant uptake based recommendations  are doing better than soil test based models. Based on yield level farmers could judge the fertilizer requirement .We need to take forward many of the new approaches to farmer field level for adoption and they should be cost effective for use.

It is very much true that nutrient availability in soils is soil- and crop specific. The best way, I think is first to decide whether nutrient availability is required for farmer advisory or one is interested for his/her research purposes.

The best way is to calibrate the available methods of nutrient estimation may standardized for the native conditions.  Dr. Alan P Newman ·and Dr. Paul Milham have very comprehensively and accurately has elaborated this aspect.

Dr.Ghafoor ,the present  day soil test methods are serving their purpose. With all the good research work done in this field we are not moving to new methods and procedures.Soil test has not become a  powerful ,rapid and simple technique to meet the needs of millions of  farmers.The biological and physical properties  are not being analysed in the soil testing laboratory. These are required to provide farmers a report on their soil health.In stead of several soil test methods one universal soil test method can be used in soil testing lab and several nutrients  can  be estimated in one go which  will reduce time and use of chemicals.But estimation methods need costly instruments.So soil test methods need a new break  through like other new fields.

I thank all the participants of the discussion for their valuable contribution.

I thank all the participants of the discussion for their valuable contribution.

its really very good discussion..  i had given task to find out nutrients requirement (precision) of one fruit crop, hence, i am submitting i request that kindly suggest me through field trial how to find out NPK requirement.. (ex. Soil test based / target yield ...) which is more suitable Method to found NPK requirement...

 kindly make your valuable comments in this regards  

 Dr. Dinesh,I missed your question asked long back.The STCR approach is being used in Kerala ,Tamilnadu and other states even for horticultural crops.Please indicate the crop and your other requirements to suggest you better way.