CN ratio plays very important role in release of the nutrients. CN ratio of 10-15 is supposed to be the best with regard to release of the nutrients and utilization.

If is the C: N ratio below 25: 1, the mineralization take a place. If the C:N ratio increased above 25: 1, it leads the immobilization. Short problem immobilization means that these organisms use nitrogen from the soil and render it temporarily unavailable for receiving crop.

Yes, as Dr Martin said, C/N ratio above 25 allow mineralization of nitrogen. But I should add that not only C/N ratio is responsible, the Total Organic Matter of the soil (TOM), ambiant temperature and porosity are also major concerns in this issue. TOM is close linked to C/N, but this last do not give a clear idea of the soil fertility status. Let's take an exemple, two soils type 1-sandy soil with TOM=0.5% in arid climate and 2-isohumic soil in temperate climate with TOM=4.5%. After amending 30T/ha of compost, they will behave diffirently even they will have the same C/N ratio (sandy soil will have the same C/N ratio as the compost 12-15, and the isohumic soil will dilute the compost in it (the same C/N ratio). The mineralization rate of the sandy soil is much higher than isohumic soil because of temperature and porosity. One last thing, in sandy soil, we have added a huge amount of microbial charge as inoculum, but in isohumic soil, even with microbial charge, defavorable conditions and high level of TOM do not seduce microbes to mineralize additional organic matter.

I've read again carefully your question and I predict two things:

1-You have a very poor soil regarding its TOM and clay content (more silt and sand)

2-If you have added only soybean, corn residue, clover, or other green manure, then it's obvious that soybean and corn residues have higher C/N ratio and result in N immobilization used by microorganisms. Adding clover or green manure is the opposit, they're fresh organic manure even with low C/N ratio, but need time be degraded at macrolevel by macrofauna (N immobilization), after that micofauna comes and start to mineralize the organic N into mineral one.

Plant presence in the soil determine microbial charge at rhizosphaera level, and add significant kinds of microfauna as complement to soil born ones in the case of high TOM in the soil (soil with low TOM will be happy to receive organic matter and plants along with sufficient water!!)

Good luck

Khalid AZIM

C/N ratio of added organic material is an important factor regulating its mineralization but is not the only factors, other factors occur especially the fibre contents, see publications about our model TAO (Transformation of Added Organics). The main factor that regulates mineralization or immobilization of inorganic N is really the C/N ratio of decomposer's organisms, which is related to that of the substrate but not really the same, see our model MOMOS( Modfelling Organic changes by MicroOrganisms of soi)

Microbial biomass and activity must be considered a primary driver of both mineralization and immobilization, not plants.  If the soil is amended with material that allows the soil to support a larger microbial population, then immobilization will increase for a time until the population reaches a new equilibrium. However, once that equilibrium is achieved, immobilization should stabilize.This higher microbial biomass, once stabilized, generally results in increased capacity to convert organic N to mineral N (since there are more of them doing it). 

I studied interactions between (partially activated) charcoal and soil in plant-free microcosms, and soils amended with higher charcoal quantities showed a much higher biomass and immobilization rate. However, higher biomass also is associated with a higher rate of N mineralization. Although the study did not directly identify the mechanism, we largely suspect high surface area (i.e. microbe habitat) was a major driver of the increased biomass/immobilization.

Using this concept, by adding organic fertilizer (which is likely to have or subsequently be converted to high surface area SOM), you are providing both a larger pool of organic N as well as potentially raising the "population limit" for microbes. N Mineralization is always occurring, but when the biomass is on the rise, the immobilization rate may exceed the mineralization rate, resulting in a net decline of inorganic N. On the other hand, if you add enough inorganic N to negate the immobilization surge associated with the greater habitat provided by the organic fertilizer, you would be likely to observe a net increase in N due to the higher biomass and associated higher mineralization rate. On top of this, there is the concept of microbial activity - a higher biomass generally means more overall activity, but not necessarily, as activity is more driven by the quality and abundance of the food source, and that can be where the C/N ratio of additives comes into play. Generally a higher C/N means more activity as measured by respiration, but not always more mineralization or immobilization of N, since N is overall less abundant. Bottom line: the microbial dynamics provide the context necessary to understand the effects of soil additives - it cannot be understood simply as a function of the C/N ratio.

The normal  C/N ratio  in soils is between 10 and 14. In this range of values, N mineralization occurs at sufficient level to provide the normal nutrition of plants with N, without the addition of N fertilizers. A too high C/N ratio led to a slowdown mineralization of raw organic matter due to predominance of carbon compounds harder degradable and hence the so-called process of nitrogen immobilization.

It is also important to remember that the C/N ratio is usually measured as total carbon to total nitrogen. Not all organic molecules are easily degraded, particularly some of the carbon rich ones. So the quality of the organic material is important. The C/N is more a qualitative rather than quantitative measure of substrate quality and the relative availability of C and N.

It's true, but I did not intend to develop the subject, I mentioned the phenomenon in general.

Plants compete with microorganisms for the inorganic N. If a plant is present and takes up N, less inorganic N can be immobilized by microorganisms. In that way, net N mineralization may increase when plants are present.

Plants do compete with microorganisms for N, but plants usually loose that competition, simply due to location... that is in part why plants mostly take up nitrate. That is all they see.

yes, C/N ratio control mineralization and immobilization. When C/N ratio is exceed 1:10-12, immobilization favours. Mostly of carbon is used for building of body of the microorganisms. 

Certainly mineralization and immolization have relation with C/N ratio. What i feel low C/N ration indicates mineralization of nutrient (nitrogen) and vise versa. You can view the landmark paper published in Nature by Prof. J.S. Singh et al. 1989. published in Nature (london). Paper attached.

Whether N is mineralized or immobilized depends on the C/N ratio of organic matter added to soil. The soil microorganism required N in a C/N ratio of about 8:1. When organic matter with very wide C/N ratio like grain straw, saw dust etc. are used in soil; a portion of soil nitrogen is utilized by the growing population of soil micro organisms. This is N immobilization. But gradually microbial activities subsided as the decomposition proceeds to end and the immobilized N, which presents as proteins in the microbes can be mineralized back to plant available form. The N content of the organic residue being added to soil can be used to predict whether N is immobilized or mineralized. In general 1.5 to 1.7% N in residues are sufficient to minimize immobilization of soil N in aerobic soil. In case of anaerobic situation, only 0.5% N is sufficient to minimize immobilization of soil N.

The C/N ratio of a substrate plays a major role in mineralization and immobilization processes of nitrogen in soils.When the C/N ratio is less than 20/1, there is net N mineralization, meaning that not all the released mineral N is immobilized by microorganisns for their metabolic activities.Some is left and released into soil and made available for plant uptake.However,when the C/N ratio is more than 30/1,i.e wide C/N ratio,no mineral N is released into soil meaning that all the mineralized N is used up by microorganisms for their metablic activities . This is what is known as net immobilization. At this level,the microorganisms go as far as using the siol-borne mineral N.

To some extent, Yes. N still is the limiting nutrient in terrestrial and marine ecosystems. So, it is strongly absorbed (immobilized) from soil solution by soil biota. The mineraliStion needs decomposers to make N available. There is a sort of equilibrium. Soil scientists have to keep it working with no disturb!

All the best

Mikaeel

Does using Fresh manure induce nitrogen immobilization?!

It depends on the C:N ratio allso. The main problem is that the nitrogen still the limiting nutrient In.Both terrerestial and marine ecosystems. So, one can strongly expect a great competetion between soil biota. So. The immobilization will overcome the mineralization of such vital element.

All the best

Mikaeel