Before you think about conversion, I would suggest that you should study critically about the usefulness of available nitrogen in the soil. To my knowledge and experience, there is hardly any utility of quantifying available nitrogen in the soil. No good correlations have been reported between available nitrogen in the soil and response to fertilizer nitrogen.

there might be one for a particular site, but never in general!

Soil organic C and available N are two different properties and one  property can not be used to determine the other. For the easiness of your work you may use the some rapid test method as soil test kit, however this provides a rough idea about available N in soil.

People are using C N ratio for calculating N content based on organic C but that is a wrong way. If you want to analyse only for available N, then use KELPLUS instrument which is based on alkaline permanganate method. You can analyse 50 samples per day provided you work 7 hours. 

Please go throuh the following publication, It may help to you.

Estimating Soil Organic Matter and Available N : A Ready Reckoner for Soil Testing Laboratories

Article Estimating Soil Organic Matter and Available N : A Ready Rec...

 Dear Basavaraj,

Thank you i already gone through the manuscript but we unable get what we need for STL.

There cant be  such relation , invariably applicable to diversified soil types.... 

You may find out the relation but it is location and soil specific. In arid soils of India, Aridisols, we find it between 0.22 to 0. 4% in general. However it varies with your cultural practices and cultivated crops.

I agree with all there is no exact relation between organic carbon and available N. But if you covert organic C to OM may  get a relation particularly for total N, we did the same in our lab. I think there is another research was done on prediction of total nitrogen based on soil organic carbon but this relation different from soil to soil. I mean you can make a correlation to get what you want because the direct conversion factor is difficult to obtained.

 Very interesting question, most of STV provide SOC, total N, the intention is to assess mineral N in terms of nitrate and ammonium, which generally can be related to available N with soil moisture, soil temperature, pH, EC and there are some crude relations in this regard

but your question, relating SOC or total N with available N, which is difficult as depends on the soil texture, cropping system, climatic conditions, management options etc, although general assessment is there

We modellers always face this problem, as we require mineral N at the time of sowing, and we have to make a rough approximation or carry out sensitivity analysis for the realistic estimates

very good question, need to be explored or to develop pedo-transfer functions through big data bases

The paper of Dr Tapas is very well appreciated in this regard, great

regards

The available nitrogen  in upland soils in Japan can successfully be estimated from the hot water extractable carbon.  The extracted organic matter has same values of C/N ratio (8.5±1.6) and likely to have high mineralization potential.  The conversion factor from TOC to available nitrogen, generated in 4 weeks incubation, is 0.046 in case 48 Japanese soils.

http://agriknowledge.affrc.go.jp/RN/2010831719.pdf

Dear Dr Yusuke

nice paper, but in japanese, only summary i could go through and looks very good, conversion factor of 0.046from TOC sounds very good, but in how much time this availability conditions and on wheat biotic/abiotic factors it depends, i compliment you for this work and the need is to derive pedo-transfer function to derive available N.

Kind regards

naveen kalra

Unfortunately the authors don't write in English as well as they don't provide the rate (speed) of mineralization .  The available nitrogen in this paper is mineralized nitrogen by 4 weeks incubation under aerobic condition  30C, which is the standard method in Japan.

Please refer Curtine et al (2006) as well.

https://dl.sciencesocieties.org/publications/sssaj/abstracts/70/5/1512?access=0&view=pdf

Conversion factor can be formulated for each and every soil. One factor is not applicable for the all soil types.

Before you think about conversion, I would suggest that you should study critically about the usefulness of available nitrogen in the soil. To my knowledge and experience, there is hardly any utility of quantifying available nitrogen in the soil. No good correlations have been reported between available nitrogen in the soil and response to fertilizer nitrogen.

To the best of my knowledge, there is no generic relation between SOM and available N. Even it is hardly to quantify available N in the soil that can be used in deciding fertilizer rate. At specific site, you can generate a relation between SOM and total N.

@Prof. Bijay Singh - I agree that the quantifying the available nitrogen may not help to establish a good relation between av.N and response to fertilizer N. This incompatibility may be due to the underestimation of ammonium ions that are fixed in the K-fixing clay minerals. The present method of estimation of av.N uses alkaline permanganate solution which is unlikely to take care of fixed ammonium ions.

Only total soil N is related soil organic carbon through C/N ratio. It can range from 10 to 30 or more depending on the type of organic materials.

Difficult question because it is too large. Is it C and N from the humus or from an added manure ? Is it a paddy soil or a non saturated soil ? Is an andosol, a vertisol or a brunisol ? Is it a lab experiment with constant temperature or a field experiment ? winter ? summer ,? moist ? dry ? On earth ?