Dear Mr Singh,

in Europe, especially in Germany and Austria, we work with the Nmin-method. There you extract mineral associated nitrogen (NH4+ and NO3-) with a KCl-solution and the determination is done by photometry.

Kind regards

Dear Dr Singh it is true that there is no suitable soil test for nitrogen generally nitrogen is recommended based on organic carbon content of soil.  Leaf color chart though would be a good method but for it lot of calibrations do data are required as color of leaf varies with varieties and also with age of the crop as well as it is also influenced by presence of other nutrients and their interation

 However there is no harm in trying to perfect this  technology for wider applicability

Due to the short time-response, leaf greenness trait seems appropriate in assessing plant N status, and driving in-season N fertilization in small-grain cereals. We have been using the portable Minolta SPAD-502 reader on wheat & barley for several years. In those cereals, the SPAD reader  measures leaf greenness, but at the same time extracts information about leaf expansion and LAI. Consequently, SPAD values at pre-booting stages may predict biomass and/or grain yields. 

I do agree with Dr Yadav.  In most cases we can not rely on soil extractable nitrogen. However, soil organic matter and the mineralization-immoblization turnover rate prove as a reliable method. Gadgets like leaf color chart served the purpose of increasing N-use efficiency. However, it needs calibration for all varieties. From my opinion, including an element of biomass along with greenness can broaden its reliability.

I agree with Dr. Yadav but it is possible to more calibration with varieties. The greenness of  same variety is deffer in different types of soil fertility status. So that LCC would be better option for sustaining cereal crop yield. However, it needs to demonstrate on farmers fields.   

I also agree with our learned colleagues , we need calibrate heavily on a variety of crops and soils in response to varying fertilization levels to add that required robustness and dynamism to use LCC as a reliable tool of fertilizer N management . No doubt , this is the most ominous gap in our current understanding on fertilizer N management , especially in cereals. However in perennial crops , it has altogether different dimensions...

Agreed jut 

LCC is a diagnostic tool for N management especially cereal crops based on the photosynthetic pigments. soil analysis results highly variable with different moisture condition.In this context we want to develop a real time tool based on the pigments content in leafs  and suggest N requirement  for different crops 

It should be tried and perfectedto increase n use efficiency in cereals

CIMMYT is now studying the use of optical sensors for nitrogen use efficiency in Pakistan:   http://www.cimmyt.org/crop-sensors-sharpen-nitrogen-management-for-wheat-in-pakistan/ 

Lot of finding are available in research articles for increase NUE how to used by farmers so that its benefited. Otherwise  its finding are useless. Now farmers are using broadcast of urea application even basal application also.  So that LCC  should be given to farmers and its used in our crops. 

IPNI has started advocating LCC to be used at farmers field  in northwest and eastern India for N-management . Results are really very encouraging Dr Yaduvanshi..

Lcc is a dopjiscated technology. Farmers need to be trained for its precise spplication

Simple nitrogen application technology in soil be developed for use by farmers

Interesting work ...

ABSTRACT: Plant-based diagnostic techniques such as chlorophyll meter (CM) readings and nitrogen (N) leaf concentration are used to determine the level of crop N nutrition, but research is limited on perennial crops and especially on aromatic and medicinal plants such as Greek oregano (Origanum vulgare spp. hirtum). The objectives of this study were to determine in a perennial crop species whether there is a relationship between the CM readings, N leaf concentration, and N use efficiency (NUE) and to use CM readings as a diagnostic tool for predicting dry matter yield in response to N fertilization. The CM readings varied across environments, growth stages, and fertilization treatments and were correlated with NUE. NUE was also affected by the environment, N fertilization, and interactions among these variables. This study provides new information about the effect of N application on CM readings, N leaf concentration, and NUE in a perennial crop such as oregano.

Source ; JOURNAL OF PLANT NUTRITION

2017, VOL. 40, NO. 3, 391–403

http://dx.doi.org/10.1080/01904167.2016.1240200

Thank you

Are the leaf colour charts or other gadgets univeral for use on different crops? If they are crop specific, for how many crops the leaf colour charts are available?.Are there variations within a crop based on soil, season, crop duration ,irrigated or rainfed etc?Are these variations captured in leaf colour charts for use under different conditions?

Colleagues,I have located a recent publication on use of chlorophyll meter(SPAD-502) to assess N status nondestructively in rice crop.Quantitative relationships were established between chlorophyll meter readings and plant N based parameters (plant N concentration,N nutrition index,accumulated N deficit and N requirement) inJaponic and Indica rice cultivars at different growth stages.Plant N concentration and chlrophyll readings varied with N rates,growth stages and rice cultivars.The relationships between chlorophyll readings and plant N based parameters are stronger at panicle initiation and booting stages in both rice ecotypes(Japanica and Indica).Is it mean that we can use the chlorophyll meter  only at panicle initiation and boot leaf stages? I have looked into another source of information where the SPAD meter is used at  tasselling stage(between V10 and VT) of corn in Illinois.The N applied decreased with increase in Relative SPAD values(this requires seperate sample readings with skill,around 20 readings from each area of interest in a field  and a reference strip).It is not clear to me on what basis one can fertilize the crop at sowing, basal  and tillering/grand growth stages?.

Non-destructive assessment of plant nitrogen parameters using leaf chlrophyll measurements in rice.by Ata-Ul-Karim ST et al Front.Plant Sci. 7:1829 doi:10.3389/fpls.2016.01829 www.frontiersin.org

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5156736/pdf/fpls-07-01829.pdf

9.Managing nitrogen by Fernandez,F.G et al. Illnois Agronomy Hand book

extension.cropsciences.illinoise.edu/handbook/pdfs/chapter09.pdf

Colleagues,I want to see under what conditions the alkaline permanganate failed/presumed to be failed.I shall be thankful to colleagues if they provide some references on this aspect.They may also provide the details of any promising soil test method for nitrogen in Indian context which can be used /adopted in soil testing laboratories.

As we all aware that  soil nitrate N is readily available to crop plants.There has been use of soil profile nitrate level as a measure of soil N status in  some states in USA and Canada.I have comeacross a very interesting paper for managing nitrogen in different annual crops based on different nitrate tests.The following are  the details of the review paper.

Soil nitrate testing supports nitrogen management in irrigated annual crops. by Patricia A.Lazicki and Daniel Geissler published online December 2016.

https://doi.org/10.3733/ca.2016a0027

While mineral nitrate  N gives an estimate of plant- available N at a particular instance,the potentially mineralizable N gives a measure of N availability through mineralization during a crop growth.Biological measures of potentially mineralizable N estimation are time consuming both by aerobic(28 days to 30 weeks) and anaerobic methods(one week).There are  methods to give an estimate of chemical mineralizable N, like hot CaCl2, acid KMnO4, acid  K2Cr2O7 or hot KCl which showed some promise .The last method ,hot KCl received some attention in the recent past.Similar method is also available for estimating available sulphur in soil.Dr.Zhang and co-workers developed a model to estimate mineralizable N in Alberta Canada.Using the model total mineralizable N (Nt) in a year (mg/kg soil) was computed.Using calculated Nt values,potential mineralizable N maps in Alberta have been developed.The maps may hep the farmers to manage soil and fertilizer N. The following two papers may be consulted for more information.

Development of a model to estimate mineralizable nitrogen in Alberta by Zhang,M et al

www1.agric.gov.ab.ca/$department/deptdocs.nsb/all/aesa8891.pdf?OpenElement

Nitrogen mineralization:a review and meta-analysis of the predictive value of soil tests. by Ros,G.H. et al.European Journal of Soil Science,62:162-173. (/doi/10.1111/j.1365-2389.2010.01318.x/pdf)

Dr. Subba Rao has listed several chemical and biological measures of potentially available N but none of these have been found universally useful in guiding fertilizer N management in INDIA.  That is why I am of the opinion that it is high time that we should increasingly shift to fertilizer N management in cereals based on leaf colour using gadgets like leaf colour chart and chlorophyll meter.  Already enough work is available from India on the usefulness of plant based approaches. 

Dr.Bijay Singh,mineral nitrate test (upto 20cm),profile nitrate test (upto 60 cm),potentially mineralizable N (biological and chemical) have shown promise in countries like USA and Canada and those tests are being used in some states in those countries.In India we have been using organic carbon and alkaline permanganate methods for assessing th available N status of soil and recommonding fertilizers.We have soil test based recommendation prescriptions (software form and tables) for targetted yield of  all the major crops of India using alkaline permanganate method (all major states) or organic carbon ( in some state).Those are being promoted /being used by state governments in soil testing laboratories .I believe  that we have not done sufficient research work on soil tests for N (except isolated studies) especially with focus on calibration and interpretation of soil tests under field conditions (most of the studies conducted in pot culture end with correlation).I believe in soil test based fertilizer and manure recommendations for  all crops on diverse soils in different environments.But I have no reservation if plant based devices are used especially for midterm correction of nutrients in the crops where such facility is available for both balance and saving in nutrients.The following review paper gives a comprehensive picture of soil testing and nutrient recommendations in India.

Soil testing and nutrient recommendations.Subba Rao ,A. et al. 2009.Journal of the Indian Society of Soil Science,57(4):559-571.

From my experience I have seen that leaf color varied with rice varieties. In that case use of LCC for N recommendation is confusing.

@Aminul Islam: The variation in leaf colour between rice varieties is not large enough that it can influence the decision regarding application of fertilizer.  We have carried out studies keeping in mind the colour variation but we found that threshold leaf colour at which fertilizer is to be applied does not give varying fertilizer applications.  You may have a look at several publications of mine available via ResearchGate.