What's organic matter?What are the sources of organic matter?What are the beneficial roles of organic mater?classify them.

Soil organic matter is one of the 3 active pools of carbon which comprises of mass-3*10(power 15)Kg comprising of 3 main fractions:

a)live fractions:- includes phytomass,faunal bio-mass & microbial biomass.Faunal biomass being further subdivided into mesofaunal & microfaunal components.

b)the living soil biota-micro organisms,animals & plant roots.

c)resistant organic matter-chemically/physically protected.

             More than 90% soil organic matter is in resistant form although there the continuous flow of carbon from one pool to another .Generally,the system is in dynamic equilibrium with the organic matter pools remaining the same more or less with time.It's chemical composotion comprise of:-

1)Multiple carboxyl,hydroxyl,carbonyl & alkyl substitutions in aromatic rings;

2)Alkyl C chains often substituted with O-containing functional groups;

3)Aroamtic & Alkyl groups linked in random sequences;

4)Protein & Carbohydrate polymers;

5)Humic molecules.

                               the process by which organic matter is continuously decomposed & renewed is called Turnover.The rate of turnover is generally considered to follow firt order kinetics i.e.,

dS/dT=kS

               O

where,S=substrate concentration at time 't'

S    =initial substrate  concentration

  O   

K=first order kinetics.

The non-biomass components decompose at diferent rates.Eg.-sugar & hudrolysable compounds degrade within hours or days while charcoal survives  >10(power 4)years.

there are 3 different pools of soil organic matter:

1)Active fractions-it includes living biomass,some of the fine particles of detrius(referred to as particulate organic matter),most polysaccharides etc.This fraction rarely comprise more than 10%-20% of totla soil organic matter.It has alife span of 1-2yr. & it's C:N ratio=10yr.-25yr.

2)Slow fraction-It consists of intermediate properties between active & passive fractions & includes finely divided plant tissues-high in lignin & slowly decomposable & chemically resistant.It has a life of 15yr.-100yr.C:N ratio=10yr.-25yr.

3)Passive fractions-It consists of very stable materials remaining in soil for hundreds of years.It accounts for 60%-90% of organic matter in most soils & closely associated with colloidal properties of soil humus.It has alife span of 500-5000yr. & it's C:N ratio=7yr-10yr.

                                             Plant residues provide an input foto the soil organic matter ranging from 11 tonnes carbon/ha/yr. for tropical rain forest down to 0.005 tonnes for desert.60%-70% of this plant carbon is derived from the root system & is termed-'Rhizo-deposition".

Fig-appproximate composition of plant residues.

the benificial roles of soil organic mater:

a)Humis substance, acomponent of soil organic matter have medicinal properties like-Antiviral,antimicrobil,liver stimulants,reduce heavy metal toxicity etc.

b)Industrial uses of humic substance is as anti-dispersants,corrosion inhibitors,pigments in ink,in tanning leather,floatation reagents.

soil organic matter is divided into 2 types:-

1)chemically protected-there is no detailesd undrstandinf of this type of organic matter.The formation of this type involves degradation & demethylation & oxidation.It is composed of humic carbon which is at dynamic equilibrium has resistance to decomposition.Not all chemically resistant organic matter in the soil is in form of a complex aromatic carbon.

2)Physically protected:-Evidence of the prescence of this fraction becomes considerable when release of carbon-di-oxide or mineral nitrogen occurs when the soil is physically disrupted by soil grinding or shearing & compression through various forms of cultivation in the field.They are mostly in the form of polysaccharides.