Question is why , C/ N ratio of less than 20 :1 co sidered so ideal..?.Is it the microbial C:N ratio also find in equilibrium with C: N ratio of soil organic matter..??

Please follow this link for said query.

http://whatcom.wsu.edu/ag/compost/fundamentals/needs_carbon_nitrogen.htm

Please check this pdf attachment also.

The information provided by Arvind is very useful. As the pdf in the second answer shows, you can use materials of different C:N ratios in the right circumstances. In cropping systems where there is a danger of leaching of available nitrate-nitrogen out of the root zone (and eventually into groundwater)during cooler periods (say over winter), incorporation of higher C:N ratio residues can help to lock up nitrogen during this risky period, to be released during more rapid growth when warm weather returns.

 Dear Gaurav Singh

A C: ratio of 20:1 is an average value for variety of soils. This ration save the crop from N deficiency due to microbial growth at log scale.

Thats a good point Dr Gaurav Singh . The basic premise is to have an organic manure , whose C:N ratio is higher than soil C:N ratio , so that the nitrogen tagged with organic manures is available at a slower rate , as per rate of mineralization , otherwise immobilization will preponder over mineralization . Resultantly , benefits of organic manure additions will go begging.. regardless of soil and crop   

I think the ideal relation CN (mineralisation or imobilizatio) depends on when you need available N in your crop system. 

True if the C:N ratio is too high decomposition slows down.

Higher will be the C/N ratio, the wastes are recalcitrant to bio-conversion

lower will be the N 

and decomposition rate

Good reply Anil. 

C: N ratio 20:1 is ideal because it does not cause any adverse effect in soil as immobilization. CN ratio decides the activity of microbial population by providing source of C. At this ratio, metabolic activity governed by microbe alone. If value goes beyond or less to the ideal level causes deficiency of N in soil in both the causes (former cause deficiency by microbes and latter causes gaseous loss or leaching etc).

The carbon to nitrogen ratio (C:N) of manure is a very important factor that affects the whole composting process because microbes need 20 to 25 times more carbon than nitrogen to remain active. The ratio should be between 25:1 and 30:1 at the beginning. The microorganisms digest carbon as an energy source and ingest nitrogen for protein and reproduction. Softwood shavings, sawdust and straw are good sources of carbon.For details see link http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex8875

wider relations cause so called N-lock, says the N becomes not available to plants, but is consumed by the microorgansim for their own metabolism.

 Dear colleagues,this topic is much discuused one.Currently also we have been discussing this topic in  another question.The ideal C:N ratio in manure can be 20:1.Manures or legume straws with C:N ratio less than 30:1,will also decompose in soil without net immobilization of N ( pl.see references provied by Dr.Arvind Singh).From nitrogen nutrition point of view, the manures and legume straws with C:N ratio below 30:1  can be incorporated in soil without the fear of net N immobilization.But in case of manures we have also to bother about the weed seeds,pathogens etc. Well decomposed manures may have the benefit of relatively low C:N ratio(20:1 or less) but also free from weed seeds and pathogens.So from manure quality point of view the ideal C:N can be 20:I or lower.

When manure or green manure are added to soil,the labile carbon in soil undergoes decompostion and provides carbon and energy to microbes.There is an ideal C:N ratio for lablie carbon,around 22:1.There is a net rapid release of N in soil below this ratio.But above this ratio there may not be net N immobilization.But after a fewdays, net  release of N can occur when C:N ratio falls below 22:1.In the  following reference one can find a good illustration(Fig.3)  of what I said.

Labile carbon I Fact Sheets I Soilquality.org.au.

http://www.soilquality.org.au/factsheets/labile-carbon

A C:N ratio between 20-30 leads net nitrogen mobilization. Above this the mineral nitrogen is to be fixed by the microorganisms. On the other hand, C:N ratio below 20 cause very fast decomposition process resulting in amonia and soil carbon losses.  

Very nicely explain the issue, but my doubt is,  If soil have different Organic carbon concentration like 0.02 percent to 2.0 percent, the same ratio of organic carbon of manure will work equally.

Hi Gaurav,

I think the last point you raise was an interesting one. I believe, the ratio effect would still be equally there in both low and high C containing soil. When we apply manure or any crop residues, the Zymogeneous group of microbes starts to work on it and if the added material has enough N then there will be hardly any dependence on indigenous background soil N. I think you can expect the difference when you apply a wider C:N ratio material, say rye residue (C:N::~60:1). In that case microbes need additional N from the soil to break the residue (assuming that C is available from the residue). You can see a net immobilization in both low and high C soil, but the magnitude and life time of the net immobilization period as well as the decomposition rate would be very different in the two soils.

I appreciate other participants for their nice explanations.

Thanks!

Deb

Dear Gaurav,

C:N is a dynamic ratio which explains co-utilization of C and N by soil microbes. Suppose, by some means, C is lost from the soil system. Automatically, N will be exposed to microbes which are always ready to mineralize it. At this point of time, again, automatically, C:N will be restored to a value which represents a point of dynamic equilibrium. For general consideration the value is roughly 20:1.

After all gains and losses of C and N from/into the system this ratio will be maintained DYNAMICALLY.

That is the point where we call a compost "mature".

I hope this helps!

It is important to be familiar with the material used in composting. Make sure to have proper C:N ratios. Materials can be blended together to attain the proper ratio. In order to blend materials in suitable proportions several factors must be considered. Please refer following link for details:

http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex8875

20:1 for C/N is ideal because the ratio be

yond this level make the decomposition is slow down,thus the plants needs time to get benefit from the manure.On the other hand for the level below the ideal level,the manure produce more ammonia which hazardous to the plants especialy seedlings

Dr.Malhotra, very good reference attached for the use of followers and viewers of this question/discussion.

I wish to add that C:N ratio of 20:1 or less is generally agreed figure for ensuring sufficient N supply to the decomposing microbes and release of some N as well to plants.There is also literature support that manures with C:N ratio below 15:1 are more likely to give positive N mineralization after application to soil(Beauchamp and Paul,1989).Calderon et al.(2004) have also reported net N mineralization for manures,which had a mean C/N tatio of 16.(refences can be seen in attached paper.One more very important point is "It would be more appropiate to use the C/N ratio of the substrate that microbes actually use (labile C) to predict N dynamics in soils rather than the C/N ratio of raw materials applied."This point was earlier highlighted by me with illustration and attached literature in my last reply.The following paper highlights the build up and importance of the labile C in repeatedly manure applied soils.

Gross nitrogen transformations in agricultural soils after repeated dairy-waste appication.ByHabteselassie,M.Y. et al.Soil Sci.Soc.Am.J.70:1338-1348(2006) published on line  June 21 2006.

biology.use.edu/files/uploads/Faculty/Stark-J/Habteselassie2006-Rates.pdf

Dr Gaurav Singh, Dr Malhotra  and other colleagues

How does the   carbon stability in different organic manures  affect  the crop response upon their additions into the soils of varying properties?. The C: N ratio , the single most important parameter. When an organic manure is most responsive in terms of  C:N ratio  , with respect to a crop and microbes as well...?

Sir,

Narrow C:N ratio (

Carbon nitrogen C/N ration

I think that 20:1 is a good ratio due to fast mineralisation which make the plant obtain nutrients easily but when the ratio increase the decomposition decrease & the mineralisation slow down & the plant need time to obtain nutrients.

Question is why , C/ N ratio of less than 20 :1 co sidered so ideal..?.Is it the microbial C:N ratio also find in equilibrium with C: N ratio of soil organic matter..??

C/N ratio of higher than 20:1 means it is poor in nitrogen and rich in organic carbon. When we apply manures, it will undergo microbial decomposition before nutrients become available to plants. While decomposing the microbes will consume both carbon and nitrogen into their body for their own growth. Microbes have their own biomass C/N ratio. The C:N ratio of bacteria, fungi and actinomycetes range from 5:1 to 10:1. Now if applied manure is poor in nitrogen (say C/N ratio > 20:1), the microbes will immobilize soil nitrogen (if not found in the substrate) into their body in order to maintain their own C/N ratio. And subsequently the standing crop (if any) will suffer from nitrogen deficiency.