Total nitrogen classification into very low, low, medium, high, very high had been reported

http://download.springer.com/static/pdf/809/art%253A10.1186%252Fs40068-017-0092-7.pdf?originUrl=http%3A%2F%2Fenvironmentalsystemsresearch.springeropen.com%2Farticle%2F10.1186%2Fs40068-017-0092-7&token2=exp=1497701776~acl=%2Fstatic%2Fpdf%2F809%2Fart%25253A10.1186%25252Fs40068-017-0092-7.pdf*~hmac=51501621b8139e3c831e08817ad9faa26aa31a2e222c72c97c014ec7b08bf9f2

In some states, the issue of soil health card is made with ratings of very low, low, medium, high, very high for KMNO4-N

 Such low medium high categories of KMnO4-N is more guided by type of crop, yield level and nature and properties of a given soil...

I fully agree with Dr. Srivastava, Such type of classification has no meaning . For example, the classification under arid soil group Aridisol  are completely different from Mollisol, Spodosol, Alfisol etc. As rightly pointed by Dr. Srivastava it also guided by type of crop you are growing. Therefore it is better to classify your own soil depends on their crop response and yield level.

Thanks Dr Tarafdar.Such classification will infact further vary if you grow same crop on a range of soil types or different crops on the same soil type..

If crops are to be taken into account, legumes must be distinguished from cereals that do not have the same nitrogen requirements

Thank you Srivastava sir. But I hope they have already done to all Agricultural ecological zone for giving soil test based fertilizer recommendation.  

Thank you vasu. I don't understand what basis you have used for reclassification of soil available nitrogen. Earlier, it was done based on plant response to nitrogen fertilizer application.  I hope soil will have major influencing variable than plants except legume crops. 

 I dont think so. Take paddy crop alone , do we use different soil fertility ratings while interpreting soil test values ..? As i said earlier also , our soil test interpretation is really substandard . We need a robust soil teat-crop response calibration equations to suit such exercise in different agro-ecological zones...

Please find enclosed some relevant  literature , we need to replicate such efforts...

Based on fertility rate experiments at few locations by various agencies fertilizer recommendations carried out.  In this approach soil tests are calibrated into different categories such as: Low, Medium and High   groups.

 -- The general recommendation is equated to medium

 -- For soils testing low or high category the fertilizer recommendation is increased or decreased    by 25% or 30%  of general recommendation.

The three Categories of Available Nitrogen is Low – 0 to 280; Medium 280 to 560 and high > 560 kg/ha.

 The six categories of Available Nitrogen(KMnO4-N) formulated by the department of water resources, Directorate of irrigation research & development, pune, Government of Maharashtra in its document No. SSD/GL.01 Lab Manual  in the year 2009. It is as follows:

 Nitrogen Ratings in Kg/ha

Very low < 140

Low 140 – 280

Medium 281 – 420

Moderately High 421 – 560

High 562 – 700

Very High > 701

Thank You Riazuddin sir

Unfortunately , the classification of soil test values into low , medium and high  is not linked with crop yield , and that yield has be crop-based...