Microbial Processes
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Subtrates microbes degrade…
Petroleum, rubber, plastics, natural fibers, celluloid, DDR, 2-4D, BHC, PHB and Cynamide
Polyuronides
Polymeric substances consiting of uronic acid with glycosidic linkages of monosaccharides
Lignin/cellulose degradation…
Bacterial/Fungal extracellular enzymes requiring high energy and containing low N
How does physical states determine decompostability?
Dry/wet, tight structuring, easy of microbial entry, O2 and nutrients
Process of deocmposition…
Plant material colonised by fast-growing bacteria/fungi, absorbing simple compounds, more complex digested by animals, humus released as residual matter
How is CO2 formed?
Aerobic respiration Anaerobic fermentation
How does CO2 lower pH?
Carbonic acid formation
What does CO2 acidification promote?
Mineral weathering and plant nutrient release
What does lowered O2 in soils promote?
Root diseases organisms, bacterial production of inhibitors like ethylene
Humus
Product of colloidal organic decay products accumulating due to slow decay
What is the process of Humification?
Breakdown of large polymers Aggregation due to humic colloids binding to clay particles Phenolic compounds main component Cationic chelation
What’s derived from H+ release aciditiy?
Cationic chelation, pH buffering, pH dependent suraface charge with oxidation increasing carboxyl groups in tandem with reactions wit phenolic OH groups
How do carboxyl/phenol groups regulate acidity?
Carboxyl release/accept H at pH between 4-6.5 whilst phenolic at 7-9
CEC increase with humus?
When humus releases H+ raising pH, and vice versa with decreasing pH
Humus and metal immobilizaiton…
Negative group chelation of Cu, Zn, Co, Ni and Mn
Organic matter decay and nitrogen release…
N as free ions, ammonium, NH4 or immobilised N as ammonium and Nitrate
What does N release to soil depend on?
How much N is provided to decomposers, N resulting from residual overcompensation.
Effects of nitrogen deficiency
Limited plant growth, microbial growth and decay process
How can N net release/immobilisation be predicted?
C/N ratio, below 20 or percentage above 2.5 is released
Importance of Nitrogen?
Plant growth, leaving a layer of mulch on the topsoil seperating soil water and altering N decay
Plant decay and C/N ratio…
It allows soil microbes to lower C/N ratio to release nitrogen again.
What does decay rate depend on?
Properties of OM, amount of OM and environmental factors
How does environment infleunce decay?
Water increases decay with wetter soils, dry limiting bacterial activity. Temperature decreasing respiration below 20C and increase 2x for every 10C O2 concentration at 10% slows aerobic decomposition Accessbility, organisms within pore spaces being too small for bacteria to enter
Why is soil OM management important?
Disposing OM like crop residues/urban waste Improving N/S supply, water/cation retetnion, soil structure Alleviate clay and poor structure effects on water infiltiration and aeration