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Is organic matter decomposition dependent upon C:N ratio ?

What is the effect of C:N ratio on decomposition of organic material? Is a high C:N ratio better or lower?

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  • Hossein Ghadiri · Shiraz University
    C:N ratio is definitely an important factor in organic matter decomposition. However, moisture and temperature availability is even more important factor. In conservation farming where you have a huge amount of crop residues present, a good C:N ratio creates a better condition for organic matter decomposition provided that you have adequate moisture and temperature.
  • Michael Astera · soilminerals.com
    ......and having adequate Sulfur largely determines whether the end result of the decomposition process is off-gassed as CO2 and ammonia, or becomes stable humus.
  • Mohamed Abbas · Benha University
    Yes, but other nutrients as P should be found in enough available concentrations in soil for stimulating the microbial decomposition for the organic matter
  • Michael Astera · soilminerals.com
    All of the necessary nutrient minerals should be in at least adequate supply, but Sulfur is the key to preserving organic matter as humus. Here's a quote from Gary Zimmer's "The Biological Farmer":

    One pound of S complexes with sex to seven pounds of N.
    Six to seven pounds of N complex with 60 to 70 pounds of C.
    60 to 70 pounds of C complex with 100 to 125 lbs of humus.
    [Zimmer, "The Biological Farmer" Acres USA 2000, pp 156-157]

    Sulfates are readily leached from the soil, as well as taken up by crops. In my experience they need to be added every year. I like to see a minimum of 50ppm S.
  • Michael Astera · soilminerals.com
    That would be "six", not sex.
  • J. Azeez · University of Agriculture, Abeokuta
    Yes, C:N ratio is one of the major determinant of organic material decomposition in the soil. Many of the scientific reasons adduced for this has been mentioned by earlier contributors.
  • Dr. Bashkim Lushaj · Ministry of Economic Development, Trade and Entrepreneurship (MEDTE) & Faculty of Civil Engineering (FCE)
    Leonardus Vergutz
    I agree you!
  • Lorenzo Menichetti · Swedish University of Agricultural Sciences
    If you talk about soil, the answer is as usual not unique.
    A citation classic in this sense is Fog (1988), but still more recent papers (e.g. Knorr 2005) are not so distant from that one. The answer is of course: it depends.
    It depends from where you are, basically, including the local nutrient conditions and the other stabilization mechanisms effective in your environment.
    As a general "law", Knorr notice that decreasing the C/N ratio (increasing N) stimulates decomposition for high-quality (low lignin) substrates and in case of systems with low ambient N deposition, while the opposite was true with high N deposition levels and for low-quality substrate.
    But I suggest you to search extensively in the literature to find a study that might be close to your environment, and then try to understand the possible causal connections you might have with edaphic factors. The C/N ratio is a really powerful (meaning effective) indicator related to decompositiona lso because it is quite syntetic and infuences (and it is influenced) by a lot of factors, and can be just a high-level answer to your research question.


    Fog, K. (1988). The effect of added nitrogen on the rate of decomposition of organic matter. Biological Reviews, 63, 433–462.

    Knorr, M., Frey, S., & Curtis, P. (2005). Nitrogen additions and litter decomposition: a meta-analysis. Ecology, 86(12), 3252–3257.
  • Kamal Karim · James Hutton Institute
    If the C / N ratio of organic material added to soil exceed about 25 / 1, the soil microbes will scavenge the soil solution to obtain enough nitrogen. Thus, the incorporation of high C /N residue will deplete the soil’s supply of soluble nitrogen, causing higher plants to suffer from nitrogen deficiency. So with increasing C/N ratio, decreased soil organic matter decomposition.
  • Durai M V · Indian Council of Forestry Research and Education (ICFRE)
    Yes, C:N is one of foremost factor in decomposition of organic matter. the rate of mineralisation and immobilization of nutrients is depend up on C:N ratio only. When C:N ratio is higher than optimum, there is immobilization process will dominant and vice-verse. If Om has low C:N (4:1), decomposition and it is high, slow rate & immoblization process become dominent example, maize straw (>80:1).
  • Kunuthur Reddy · Natural Farming Centre, Mamillapalle,Andhra Prdesh, India
    The C:N ratio keeps on changing and it is a dynamic process controlled by moisture, temperature, aeration, quantity and diversity of organic matter, decomposition rate, microbial density and diversity. Narrow ratio is favourable to rhizosphere since it becomes stable. Addition of organic matter with narraow CN ratio is a good practice for soil development.
  • K.K.I.U. Arunakumara · University of Ruhuna
    Certainly yes, C/N ratio of the material is the key factor for successful compost production. The topic has been extensively investigated, thus number of research findings are available covering many aspects
  • Robert Moore · Recycling Organics International, Inc.
    Wish to express my appreciation to all for providing their viewpoints. As a professional soil/compost microbiologist and life-long composter/farmer-gardener, my 'take' on C:N is a bit different than most of you, Your patience is solicited as I attempt to phrase my input from a layman's perspective rather than a technical one - since hopefully there will be some non-technical farmers/gardeners watching this tread that need to understand some basic C:N methodologies in the effective practice of utilizing their crop/livestock residues to enhance their soil/dirt in order to enhance their crop yields while lowering their use of synthetic chemical pollutants (and associated costs).

    Certainly multiple sciences (physics, chemistry & biology being foremost) are involved in the decomposition of organic MATERIAL into organic MATTER and thence into HUMUS (compost is NOT Humus, although if properly managed, can contain a high proportion of it - in its well-aged state) - Humus being the FINAL amphorous (without shape/form) result of microbial activity - one of the most complex carbon-chains known to science (science does not have that chain 'figured-out' yet).

    Several of my learned colleagues have already given the "correct" answer to the C:N question - which in my opinion is: DEPENDS.
    Depends on a HUGE number of factors (more than are noted in this offering) such as the type/mix of feedstocks (each having their own C:N ratio dependent on time/age of the material as N volatilizes/leaches); percent of moisture (specifically the dissolved oxygen content available to microbes IN that water; (microbes don't 'breathe' air like humans - and someday the commercial composting industry will 'wake-up' to that fact - but I empathize with them, because the composting industry is severely hampered by antiquated, un-scientific State regulations that are (for the most part) NOT based on current science; and IN THE END, the C:N 'answer' is dependent upon the MOST IMPORTANT aspect - the density and diversity of the microbial community (the individual needs of the bacterial/fungal/ [and in some cases protozoan] communities) that actually perform the saprophytic decomposition work.

    It is VERY difficult for ANYONE (even researchers/scientists) to estimate the actual C:N ratio of even a single large quantity of the same feedstock (without using complicated lab testing) - much less a mix of multiple feedstocks because each individual ratio (ergo the total) can change DAILY. MUCH too complicated for the people who actually must perform the activity of bio-degrading their organic residues. Fact is: one uses what one has to work with. The objective then, is to enable/facilitate a given (mix of) feedstock to be 'eaten' by microbes - (technically the microbes themselves don't physically 'eat' feedstocks - the ENZYMES they produce do that) and it takes a 'community' of microbial enzymes to perform that function efficiently.

    So permit me to offer some suggestions for utilizin...
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  • Azubuike Chukwuka · University of Ibadan
    Quite an extensive recommendation you have here Robert, but i would like to ask if there is any information on the cost effectiveness and sustainability of these options if applied to the agricultural sector.
  • Robert Moore · Recycling Organics International, Inc.
    Azubuike,

    Regarding SUSTAINABILITY:
    Comparatively, organically improving cropland and crops with live biological treatments resulting from organic recycling is certainly sustainable (renewable) - whereas use of agricultural synthetic chemical treatment derived from crude oil processing - is not sustainable in the long-term (at some point in the next century, oil reserves will become severely depleted) nor in the short-term.as the price of crude oil continues to drive the ever-increasing cost of food/forage/fiber crop production - borne by consumers - to whom, in this present economic time, presents a tenuous situation - particularly to low & fixed income households.

    Another sustainability issue is the rampant global pollution of soil and water resources by long-term overuse of synthetic chemical fertilizers - along with severe erosion issues caused by a number of reasons - including the loss of microbial soil community from application of biologically-damaging chemicals to both plants and soil.

    Regarding COST-EFFECTIVENESS:
    Cost-effectiveness is certainly the bottom-line issue for the plant production (agriculture and horticulture) industries and the commercial composting industry that serves both those sectors.

    Certainly the world populations need to become more aware of the need to do a better job of recycling organic resources instead or burning or burying them. Returning organic material to the earth (in one form or another) to replenish the biological component in soil can most certainly be done cost-effectively (use of time, energy and money - to increase crop harvest volume and nutritional quality - regardless of scale. A matter of innovation - the mother of invention...

    By using the word 'information' rather than 'data' or statistics' I presume you are asking how much each of those options I presented - cost to implement? Both capital expense and operating costs are a matter of scale - so the answer you seek depends on identifying that scale.

    I do not know the extent of your expertise in this arena, but as a aquatic toxicology PhD candidate, I will assume a lack of basic saprophytic microbial process understanding - so PLEASE do not be offended by my very basic explanation if you are more skilled in composting than I surmise.

    Since you did not provide any specific example, allow me to present one broad example in the interest of directing your question toward specific answers:

    PARTICLE SIZE REDUCTION:
    The purpose of reducing organic material particle size is to expose greater surface area to immediate microbiological decomposition, thereby significantly speeding the process - time is money. At the horticultural level, the most common tool is a machete - which involves mostly time and physical energy. At the small farm level, a small machine should accommodate the volume (the most common machine in that category is a hammermill chipper/shredder - the size/power/cost of which is relative to volume of material needing to be pr...
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  • Daniel Deng · University of Southern Mississippi
    It depends on the time and the habitat where microbes living. Initially, low C/N ratio material is easily decomposed and can prime the rapid growth of general microbes, while during later decomposition process when microbes reach higher density, the decomposers can find other N sources from the environment (eg., or may synergistically interact with N-fixing bacteria).
  • Azubuike Chukwuka · University of Ibadan
    Thanks Robert, you did justice to my question.
  • Raveendra Patil · University of Agricultural Sciences, Dharwad
    To answer in one sentence, YES it depends on C:N ratio. Wider the ratio slower the decomposition rate and vice-versa.
  • Robert Moore · Recycling Organics International, Inc.
    I prefer the answer: "Depends" (upon multiple factors - as noted).

    However, the answer "Yes - within C:N range limits (not too high or low) AND following first priorities - as noted" is also substantially correct.

    First priority is that moisture must be present (with DO content) needed to ascertain C:N and provide microbes with an environment conducive to decomposition activity).

    Second, the issue of particle (surface area) size that can change C:N nutrient availability to the microbial level.

    Third, the entire question of C:N nutrient availability is relative to the density and diversity of the viable (not dormant) existing (and/or inoculated) microbial community available to act upon (mainly the surface area) of compost feedstock material (without the full synergistic community, decomposition will not (if sterile/contaminated) occur even with a 'perfect' C:N ratio).

    In addition, existing C:N is dynamic and can be altered (on-the-fly) by adding appropriate microbially-available carbon and nitrogen (in soluble form) to alter immediately-available C:N nutrients (to the microbial community) within the range desired. Meaning that decomposition rate is not totally dependent upon (nor limited to) the existing C:N ratio of a given feedstock (or mixture thereof).
  • Peter Weishampel · National Ecological Observatory Network
    C:N can be a good predictor of nitrogen mineralization and decomposition rates, but the quality of the carbon matters. Lignin is slow to decompose, cellulose is less slow, simple sugars, even less so. I've seen lignin:N used as a better predictor, but lignin is not as easily measured as total carbon. Higher C:N (or better yet, higher lignin:N) slows decomposition, all other factors (e.g., decomposer populations, water content, temperature, pH, etc.) being equal,
  • Robert Moore · Recycling Organics International, Inc.
    Peter,
    "...all other factors (e.g., decomposer populations, water content, temperature, pH, etc.)" are NEVER equal...
    But do agree with you that : "the quality of carbon matters."
    For high-cellulosic/lignin composting feedstocks, pre-treatment with soluble nitrogen. to 'kick start"' the microbial decomposition process (by balancing the C:N ratio) should be considered.
  • Asmeret Berhe · University of California, Merced
    recent evidence in the literature is challenging the previously widely held idea that molecular composition (including C:N, lignin:N ratios and similar metrics) alone can strongly regulate decomposition of organic matter. The dependence of decay rate on C:N ratio is likely in the short-term and co-evolves with the physical conditions in the environment decomposition is taking place. Evidence is now mounting that, in the long term, physico-chemical and biological influences that OM encounters in the environment play important more important roles in reducing its likelihood for decomposition and other loss processes (including leaching and erosion), compared to its chemical compositions.
    for more discussion on this see Schmidt et al 2011, Nature.
  • Akwilin Tarimo · Sokoine University of Agriculture (SUA)
    Looking at your question from the agricultural point of view, I see two competing needs for N. One is the need for soil microbes to feed themselves and two, the need for the crop, for example for nitrogen fixation in a legume crop or legume-cereal inter cropping system. Increasing nitrogen availability in the soil reduces competition for the this nutrient during the process of residue decomposition, which could mean that decomposition would proceed as determined by soil temperature without depriving the crop of the nitrogen needs at any particular stage of growth.

    When C:N ratio is at equilibrium, the rate of decomposition of organic matter is determined by soil temperature and nature of the plant residues and hence, N availability to the crop. This latter N becomes largely available from the decomposed organic matter. Thus, high C:N ratio may influence the rate of organic matter decomposition but caution should be observed when using straw residues as mulch for dual purpose of soil enrichment and protection against high air temperature and torrential rain storms. One should ensure availability of a starter-N to stimulate microbial activity for future synthesis of N from the residues. From this discussion it appears that high C:N ratio would be good for organic matter decomposition in the soil through enhancement of microbial activity. The rate of the process will eventually depend on the nature of the residues, soil temperature and soil water. I hope my contribution will stimulate further discussions on this important topic.
  • Antonin Kusbach · Mendel University in Brno
    Got your question later, but I hope my explanation may help. A lot has been told above, from forest ecosystems point of view: I think that C/N ratio is just expression/index of complex conditions (e.g., climate) affecting organic C and organic/inorganic N. It can not affect a decomposition rate itself. It traditionally serves as a rate index. In forest soils of the North Hemisphere, for example, there are humus layers (litter/duff etc.) on a mineral soil. The harsher climate the thicker humus (boreal forests, high mountain conifer forests) because of low temperatures, microbial activity etc. and thus low decomposition and digest of OM. Contrary, Mediterranean warm oak forests have almost no litter because high decomposition rate of oak leaves in warm convenient climate.
    So, you might ask better: what stands behind fast/low decomposition of OM and how C:N ratio reflects that?
    Tony
  • Robert Moore · Recycling Organics International, Inc.
    OM decomposition is almost entirely microbial in nature (pun intended). Both the degree and rate of microbial decomposition of OM is dependent upon diversity of and density of the microbial community that 'does the work', which is primarily factored by the environmental conditions within which the microbial community depends - to establish a consistent reproductive rate over time.
    Very basically, carbon (for energy) and Nitrogen (amino-protein to build cells) usually expressed as C:N, along with O2 in water are required for aerobic microbial reproduction - requiring a sufficient supply of of all three basic elements (along with other adjunct factors such as mineral availability) to act efficiently on OM,
    So the answer to the posted question is YES - BUT DEPENDS on the extent that other primary factors are also present (since C:N is not the only primary factor).
  • Antonin Kusbach · Mendel University in Brno
    Robert, thanks for the great complement.
    T
  • Anand Singh · Panjab University
    Very interesting question!
    My answer is in conformity with Robert Moore. Because organic matter (OM) decomposition is a complex mechanism, it is govern and regulated by microorganisms. Conversion of organically bounded material (carbon, Nirogen and Phosphorus) into simpler form is known as mineralization. Normally, microbes prefer to decompose nitrogen and phosphorus rich litter instead of rich carbon. Carbon is however an essential need for getting energy but microbes prefer building element like N and P.
    Based on my experience, decomposition rate would be faster of those litter will contain high quality and quantity of of N and P instead of Carbon. But C:N ration will not be whole sole reason, there would be some other determinant factors which may govern rate and rapidity of organic matter decomposition.
    Conclusion: Microbes prefer to decompose very fast litter which contain high quality and quantity of N and P.
  • Preeti Roychand · La Trobe University
    Yes organic matter decomposition depends on C:N ratio. If the C:N ratio is too high in case of sawdust then decomposition is low and if it is low in case of peastraw then decomposition is high. It is due to more water soluble carbon avaiable for microbes.
  • Anand Singh · Panjab University
    @ Priti Roychand,
    C:N ration an important parameter to know basically carbon and nitrogen concentration present in the litter. I am agree with you that C:N ratio play good role in the decomposition but widening of the C:N ratio also indicates the quality of litter. For example, a litter has 0.1 percent nitrogen and 48.0 percent carbon then C:N ratio would be 480, at the same place, another litter source collected from a leguminous plant shows 48.0 percent carbon but 4.5 percent nitrogen, here C:N ratio would be 10. Now decomposition rate will be faster in the latter one and slower would be in the first litter type. It is because of C:N ratio.
    However, I can say with evidence, for decomposition except C;N other factors are also responsible for faster decomposition.
    In some case cases, especially from desert environment, C:N ratio of available litter in the desert ecosystem exhibited a favourable C:N ratio which may favour but oppositely it showed slow decomposition. It is because of other factors which are responsible such as moisture and kind of saprophytes available in the soil environment there.
    Yes it is very true: It is due to more water soluble carbon available for microbes. I quote your last sentence as a conclusion.
  • Robert Moore · Recycling Organics International, Inc.
    Many speak of C:N as a static issue - but it is not. C:N is a DYNAMIC component of the decomposition process - constantly changing naturally, due to changing environmental factors. But the point is: C:N is a component that is easily adjusted "on the fly". Consideration of the C:N ratio in the field is pure 'guesswork' - only 'definable' in a laboratory - hence a value-judgement issue. Both nitrogen (in the form of amino acid proteins) and carbon (usually in the form of simple sugars) used by the microbial community to reproduce, can be inoculated in liquid form to alter the C:N to more favorable microbial reproductive conditions - hence faster decomposition rate. Also adding additional LIVE aerobic microbes to feedstocks via liquid solution - to increase saprophytic activity - is also quite simple. Therefore compostable material which might take 6-9+ MONTHS to process through the stable/finished/mature stages in a given environment (capable of beginning efficient nutrient cycling to plants and initiating effective disease/pest control) can easily be significantly time-decreased by altering the INTERNAL composting environment. Composting is a man-contrived process that simply speeds-up- the natural biological processes of nature.. It is not unusual for an experienced composter - using scientific methods - to produce high-quality MATURE compost - from RAW materials - in 8-12 weeks - depending on how well feedstocks are processed and the decomposition rate controlled.
  • Gulshan Sharma · Indian Agricultural Research Institute
    ya its sure as C:N ratio determine mineralisation.
    if C:N ratio >30 immobilisation of nutrient
    <20 mineralisation of nutrient
    if take paddy or wheat straw C:N ratio is in range of 100:1 so it take more time in decomposition. even if High C:N material wiil apply on soil it will cause low yield comparatively. so it is recommended that donot apply fresh compost or dung to soil.
  • Dr. Amanullah · Khyber Pakhtunkhwa Agricultural University, Peshawar
    The higher the C/N the slower will be the decomposition, but the higher the N/C the faster will be decomposition process.
  • Anand Singh · Panjab University
    Yes, Dr. Amanullah saheb, I am agree with you. It is because of higher concentration of N and low concentration of carbon attracts more saprotrophs. Faster decomposition of those type of litter which contain significant amount of N concentration.
  • Asafor Chotangui · Nihon University
    C/N is an index commonly used in soil science and other related fields to indicate the "rate" of decomposition of organic matter. All things being "equal", the organic matter in question should be similar (source and conditions under which they are found). Organic matter with a high C/N ratio will readily decompose than a similar material with low C/N ratio.
  • Norman Mhazo · University of Swaziland
    Let's pit facts straight. High C/N ratio means high levels of carbon and low levels of nitrogen and vice versa. Organic material with high C/N ratio means that it has low nitrogen. Decomposers, therefore, will scavenge for N from other sources for their own needs thus delaying decomposition of the organic matter.
  • Pramod Chaudhari · Grass Roots Research & Creation India
    C:N rato is the most important for microbial decomposition of organic matter in edaphic or aquatic environment. Unless and untill optimum C:N ratio (based on stoichiometry of biomass) is not provided, proper decomposition of organic matter would not occur. The ideal C:N raito for composting is generally around 30:1. Higher ratios mean that there is not sufficient nitrogen for optimum growth of microbial population so decomposition will be slow. In this case you have to fortify nitrogen source through nitrogen fertilizer. At lower ratios, carbon is in short supply (whole carbon is decomposed) and nitrogen is in excess and will be lost as ammonia gas, causing undesirable odours. In this case it is necessary to incerease organic matter conctent in the compost.
  • Ben Thomas · McGill University
    I think the C:N ratio of the bioavailable fraction is most important.
  • J.A.E. Molina · University of Minnesota Twin Cities
    Try that relationship:


    C------NITROGEN REDUCTION FACTOR ON EXOGENOUSLY ADDED OM (RESIDUES) DECAY (RTF(I)>0).
    C ------------------------------------------------------

    C---------RTF(I) IS THE N LIMITING REDUCTION FACTOR FOR EACH RESIDUE (I)
    C---------COMPUTED AT EVERY TIME STEP
    C---------CNRATE = RATE OF C OUTPUT FROM EACH RESIDUE
    C---------DIVIDED BY (NH4+NO3)-N AVAILABLE
    C---------PLUS N OUTFLOW FROM RESIDUE (I) PER TIME-STEP (REFER: '*DELTA').
    C
    DO 31 I=42,45
    XNCN=CONC(18)+CONC(21)+((RED*CF(I)*CONC(I)*DELTA)/CN(I))
    IF(XNCN.LE.0.) XNCN=.001
    CNRATE=(RED*CF(I)*CONC(I)*DELTA)/XNCN
    IF(CNRATE.LE.10.) RTF(I)=1.0
    IF(CNRATE.GT.10..AND.CNRATE.LE.20.)
    1RTF(I)=(1.0-0.70)*((CNRATE-20.0)/(10.0-20.0))+0.70
    IF(CNRATE.GT.20..AND.CNRATE.LE.50.)
    1RTF(I)=(0.70-0.40)*((CNRATE-50.0)/(20.0-50.0))+0.40
    IF(CNRATE.GT.50..AND.CNRATE.LT.80.)
    1RTF(I)=(0.40-0.25)*((CNRATE-80.)/(50.0-80.))+0.25
    IF(CNRATE.GT.80.)
    1RTF(I)=(0.25-0.20)*((CNRATE-120.)/(80.-120.))+0.20
    IF(RTF(I).LT.0.2) RTF(I)=0.2
    31 CONTINUE


    conc(i): concentration of decaying exogenously added OM (i)
    of cn ratio cn(i)
    conc(18): concentration of (NH4+)-N
    conc(21): concentration of (NO3-)-N
    delta: time step
    cf(i): specific decay rate of residue
    (first order decay rate, refer cf(i)*conc(i)
    red: gener
  • Anand Singh · Panjab University
    Let me know it in simple way
  • J.A.E. Molina · University of Minnesota Twin Cities
    RTF(i)

    1.0 | *
    |
    |
    0.7 | *
    |
    |
    0.4 | *
    | *
    0.2 | * *
    |
    0.0 |_____________________________

    10 20 50 80 120
    CNRATE


    rate(i)=rtf(i)*cf(i)*conc(I)

    rate(i): actual decay rate
    of exogenously added OM (residue)
    to soil

    cf(i): specific decay rate
    at optimum conditions of decay

    conc(i): residue concentration

    rtf(i) reduction factor on
    the optimum decay rate
    computed at each time step
    of the numerical integration

    cnrate: is not the CN ratio of the residue.
    it is the ratio of
    the optimum C decayed from residue
    divided by inorganic N available:
    nitrate-N plus ammonium-N
    plus optimum N decayed from residue (if any)
    at each time step.
  • Thierry Tétu · Université de Picardie Jules Verne
    Yes but the main factor is not the C/N ratio but first the nature of the fresh C/N ratio that will influence the soil biological activities (biomass and sensus stricto activity) and second the intensity of the Rhizosphere Priming Effect (RPE) on the older organic matter, and/or the priming effect issued from the residues that affect the older organic matter on bare soil (during the fallow period or covered soils if the study concerns agriculture soils).
  • J.A.E. Molina · University of Minnesota Twin Cities
    yes and these factors have to be included in any quantitative model of C and N dynamics in soil. There is not one main factor but the whole has to be considered and integrated. Refer for example Geoderma 81 (1997) 153-225.
  • Dr. C M · University of Agricultural Sciences, Bangalore
    -Yes definitely organic matter decomposition is dependent on C:N ratio.
    - the C:N ratio of 10:1 to 12:1 is required for microbial biomass decomposition. then a well decomposed organic matter has a C:N ratio of 12:1 to 20:1. more than that is not suitable.

    Effect of C:N ratio

    First of all we have to see the type of material from which organic matter prepared.

    For example if it prepared from leguminous material the C:N ratio is narrow (10:1 to 25:1) because the presence of higher nitrogenous material in that than carbon inturn helpful in microbial biomass multiplication. from this the rate of decomposition will be faster and availability of nutrients to the plants (i.e. mineralization rate) will be more and vigorous. If you apply organic matter having wider C:N raito (cereals and coconut fronts) leads to "nitrogen depression" (Nitrogen locking in microbial body) inturn leads temporary unavailability of nitrogen in plants.

    -Then higher and lower not the matter. it should be mentioned as wider and narrow C:N ratio. for better availability of nutrients narrow C:N ratio is required than wider .
  • Elhafid Nabti · Université de Béjaïa
    indeed, it depends on C:N, I think normaly, that when C:N is better to be increased.
  • Robert Moore · Recycling Organics International, Inc.
    Kudos and plaudits to my Colleagues who commiserate and comment on this subject.

    As a soil/plant microbiologist specializing in decomposition of compostable feedstocks, allow me to interject a quandary into this discussion.

    The majority of you speak in terms of C:N ratio in relation to "microbiology" as if that microscopic community was "one being" - which it IS NOT.
    While the beneficial aerobic microbial community acts in a SYNERGISTIC manner, this microbiological community of which you speak in such 'generic' terms is actually composed of a MULTIPLICITY of different bacterial, fungal (and protozoan) species, EACH of which acts on 'organic material' in DIFFERENT WAYS (specifically via production of [and utility of] the ENZYMES they produce, which actually perform the WORK of decomposition - to solubilize/transform that MATERIAL into MATTER and eventually into HUMUS - the amphorous ultimate END to the decomposition process [as far as microbiology can take it - one of the most complex molecules known to science]. That being said, science still knows only very little of the microbial knowledge it needs to learn.
    So while some of you say that "this or that" C:N ratio pertains to optimization of decomposition rate - you should understand that no matter what the C:N ratio of ANY given feedstock material 'BALANCE' is - there are certain 'classes' of microscopic biota that are capable of acting on WHATEVER C:N RATIO EXISTS [yes, the generally-accepted 40:1 to 20:1 ratio 'range' is optimal - as long as the "BALANCE" of air (in the form of FREE oxygen) and H20 exists - without which, NO decomposition will take place (since such aerobic microbiota will be DORMANT - no matter what the existing C:N composite ratio is.

    So while C:N ratio is certainly important to decomposition rate, it is NOT the primary necessity that determines the decomposition rate of organic (carbon-based) material - but ranks only 4TH in necessity.
    OK - given that the 'proper' O2 / H20 conditions DO exist, CARBON is needed to provide energy to microbes and NITROGEN (in the form of amino acids in protein form is needed - along with some additional phosphorous and potassium) to build cells (microbial reproduction capacity) - but understand that such balance [whatever it is - is dependent upon adequate O2/H20 availability) and CAN be utilized by certain species of microbes.
    And yes, the percent of CO2 existing within the mix (which both chemistry and microbes create) is important - an over-abundance of which - will drive ALL aerobic microbes into [inactive] dormancy).
    Microbes (et al - synergistically speaking) actually CHANGE the MOLECULAR STRUCTURE of organic (and inorganic) material depending on the physics/chemistry makeup (yes, chemical reactions also occur based on the ionic characteristics of the mix too (in the presence of O2 & H2O).
    I hope this input - intended to clarify - does not confuse you...

    So as stated in my previous comments in this thread - the true answer to this...
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  • Clément Peltre · University of Copenhagen
    Note that for composted materials, the C:N ratio can be interpreted differently, since stabilized compost usually have a lower C:N ratio compared to fresh plant materials, but are more stable once applied in soil. This is due to the fact that during composting, the N and C are transformed into more stable forms...
  • Mumtaz Ganie · Sher-e-Kashmir University of Agricultural Sciences and Technology
    Sujit, of course C/N ratio is very important for organic matter decomposition. Besides lower the C/N ratio better it is for decomposition process. However there are many other factors also which govern the process but C/N ratio is of prime importance.
  • Noriharu Ae · Rakuno Gakuen University
    C/N ratios might control decomposition of organic matter.
    However, polyamide resin (called nyron) is not easily decomposed in a soil.
    please think about quality of the organic matter.
  • Ulises Lopez · Universidad Juárez Autónoma de Tabasco
    It is important to note that the C / N ratio is only an indicator of the rate of mineralization of organic matter (OM). Sometimes are not considering is the quality of the material organic , example one ton of organic material that is really far from easily degradable ie has a C / N ratio 10:1. So any other indicators that could be taken would have to consider the quality of the MO.

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