TOPIC : ORGANIC MATTER (OM)

SOIL ORGANIC MATTER (SOM) is fraction of the soil being composed by plant and animal that is remains in various stages of decomposition.

Component of OM includes living organisms, fresh residue, active fraction, and stabilize OM.

How to change OM in soil :-

1. ADDITION - when root die, they become part of OM
2. TRANSFORMATIONS - soil organisms will change the organic compounds and it will consume plant residue and OM, create by-product also.
3. MICROBES FEED PLANS - some waste release by soil organisms can be used to plant growth.
4. STABILIZATION OM - OM will resistant to the further change.

What does OM do ?

1. NUTRIENT CYCLING
• inc. nutrient holding capacity CEC
• like pool (sink) of nutrients for plants
• BIND nutrient to prevent it became unavailable for plants.
• food source for soil organisms like worm and bacteria. These organisms will convert nutrient to be available taken for plant grow
2. WATER DYNAMICS
• improve water infiltration
• decerease evaporation process
• inc. water holding capacity like in sandy soil
3. STRUCTURE
• prevent compaction
• release crusting for example in fine texture soil - clay
• encourage root develepment
• improves aggregation and prevent erosion (hakisan daaa.. huhu)
4. OTHERS
• herbicide break down quickly so, it will tie up the herbicide in soil
• it also may support for disease and pest as well as for beneficial organisms

Factors that influencing the amount of OM

1. MANAGEMENT
• practices like cover crop, irrigation and etc will inc, the amount of roots and residue added
• but intensive tillage inc. the loss of OM by speeding the process of decomposition
2. SOIL TEXTURE
• fine texture like clay will hold more OM because  :-
• clay particles form electrochemical bond that holds the organic compound
• the decomposition process will occur faster in sandy soil because it is well aerated
3. TEMPERATURE
• high temp. will speed up the degradation of OM.
• the decomposition process more rapid in tropic area compared to the temperate area
4. LANDSCAPE POSITION
• poorly drainage got high OM because oxygen is available for decomposition process
• low spots accumulate OM that erodes off hills tops and steep slopes
5. VEGETATION
• grow plant that have low C:N ratio like legumes and green manure because it will inc. nitrogen pool
• if large C:N ration and lignin content like grasses, it will cause nutrien immobilization (cannot take by plant)
6. SOIL MOISTURE
• more rain, more moist so it will inc. OM
• remember the field capacity (60%)
7. SALINITY AND ACIDITY
• if too acid or too alkalilne it will make poor biomass

Increase OM

• compositing
• cover crops and green manure
• crop rotation
• perennial forage crops
• reduce tillage or zero tillage
• agroforestry

Decrease OM

• deforestration
• over grazing
• traditional farming like monoculture
• burning natural vegetation
• excessive drainage
• conventional tillage

(to be cont.)