Sunday, February 22, 2009

Components of soil


Thick fibrous parts of plants (lignin) and cellulose (carbohydrate) are the structural parts of plants.
· Bacteria convert the lignin into humus under favorable humid conditions and presence of oxygen, nitrogen and temperature range of 15 to 25 deg cents.
· Cellulose provides energy to the bacteria.
· Under these conditions micro flora thrives and on their death their dead bodies form ligno proteins.
· Humus and ligno protein contribute towards stability and structure of soil.
· Balance in the presence of fertility elements like Ca, Mg, K and Na also enhances humification when pH of soil stabilizes at 6.5-7.5.
· This pH optimizes availability of all plant nutrients in the soil.
Fertility :
One can surmise the nutrients needed by a plant by determining the mineral content of the plants themselves. Typically, healthy plants are incinerated under controlled conditions and the mineral content in the ash is determined. This information is the basis for the formulation of complete soil.

Let us understand the nutrient content of plant, which is fulfilled through the environment.

Most plant parts are made up of carbohydrate

These come from
1. air 2. water
Now if we consider the dry weight of plants.
(This is the weight that remains constant after drying in sunlight)

If we were to consider fresh biomass, the weight of the same is called “fresh weight”.Allow it to dry under sun, weigh it on alternate days. In a span of five to seven days when no loss of weight is observed, that is the “dry weight”. (“Dry weight” includes some quantity of water called “constitutional water” which is equivalent to 60 % of the dry weight.)

Weight of fresh biomass “fresh weight”

Weight that remains constant after drying ‘dry weight’

If we consider:
100% dry weight of plants
44% --- carbon
44% --- oxygen
6% -- hydrogen
4% --nitrogen


Therefore we can say that only 2% dry weight comes from soil.
The absorption of these nutrients by the plant are influenced by:

a. Cation exchange capacity or CEC

b. pH

c. Presence of micro flora:

Presence of microbes from plant kingdom like bacteria, actinomycetes, phungus, and algae and those from animal kingdom like earthworms, snails slugs, make the soil a live soil.

· One of the major benefits bacteria provide for plants is in helping them take up nutrients.
· Others break down soil minerals and release potassium, phosphorus, magnesium, calcium and iron.
· Still other species make and release natural plant growth hormones, which stimulate root.
· Few species of bacteria fix nitrogen in roots of legumes while others fix nitrogen independently of plant association.

In a live soil maintained by proper mulching and moisture, these microbes thrive, multiply, and die. The process is a continuous chain. The dead bodies of these microbes are nothing but Humus. Therefore if the soil is maintained, there is no need for manure to be added. All that is required to be done is to recycle the residue after harvesting the crop.

Further, there are two types of bacteria present in a soil.

· Bacteria which develop locally.
· Bacteria which are introduced through cow dung, decomposable material, polluted water etc.

The bacteria which are developed locally have capacity to sustain worst condition. In unfavorable conditions they become dormant and become active again when conditions change to favorable again. Bacteria introduced from out side do not have such a resistance and they die in unfavorable conditions.
Larger organisms in the soil include a variety of flatworms, earthworms, and nematodes. The various worms play several vital roles in maintaining soil quality as predators and as recyclers of nutrients.

: - Microbes consume oxygen from soil air and give out carbon dioxide. In the absence of such gaseous exchange, carbon dioxide accumulates in soil air and becomes toxic to the microbes. Rate of oxygen intake and simultaneous evolution of carbon dioxide are measures of microbial activity. Direct sunlight is injurious to most of the microorganisms except algae. Therefore for microbes to thrive, soil should be well aerated.
· Bacteria that need oxygen to live are called aerobic, and those that survive without oxygen are called anaerobic.
· Aerobic decomposition of organic material does not give out foul smell however anaerobic decomposition of organic material results in formation of toxic gasses in the air due to lack of oxygen.
· Moisture: - In the presence of excess water, water logging, anaerobic condition occur, the aerobes become suppressed and inactive. In the absence of adequate moisture in soil, some of the microbes die due to tissue dehydration and some of them change their form into resting stages of spores or cysts. Aerobic microbes need 50-75% humidity, in air and soil; some need 90%humidity to survive. Therefore for microbes to thrive proper moisture content is necessary.
· Temperature: Temperature is the most important environmental factor influencing the biological processes and the microbial activity. When the temperature is low, the number and activity of microorganisms fall. Most of the soil organisms are mesophiles and grow well between 150C and 450C. A temperature of 25-370C is considered to be optimum for most mesophiles.
· Those bacteria, which thrive in temperatures from 45deg-65 deg., are called thermophillic bacteria. They do not survive below 40 deg.
· PH Reaction: - Bacteria prefer near neutral to slightly alkaline reaction between pH 6.5 and 8.0. In acidic or alkaline soils microbes become inactive. Some bacteria do grow in pH of 3.In acidic soil if we add lime, bacteria increases. pH of 7 is ideal for growth.
· Food: Well-aerated soil rich in organic matter is an essential prerequisite for maximum number and activity of heterotrophic (deriving its nourishment and carbon requirements from organic substances; not autotrophic) microorganisms. The microbial cells undergoing senescence (growing old) serve as a source of food for the organisms.
· Soil factor: A soil in good physical condition has good aeration and moisture supplying capacity, which are so essential for optimum microbial activity.
· C.N. Ratio: All living organisms are made up of more amounts of carbon with small amounts of nitrogen. The content of these two is extremely important in how quickly bacteria decompose organic waste. Ideal ratio of C to N is 20:1.With this decomposition process can be very quick, roughly 6-8 weeks. But all things have different C: N ratio. So a balance has to be made to create this ideal ratio. Materials high in carbon include leaves, sawdust, wood chips and straw. High nitrogen materials include grass clippings, food scraps and manure. The optimum C-N ratio for bacterial decomposition is in the range of 25/1 to35/1 . The ratio of organic carbon to total nitrogen in a soil provides a measure of the quality and rate of decomposition of organic matter. The lower the ratio, the quicker organic matter will break down, and release nutrients (including nitrogen) in forms available for plant uptake.

Thus we see that the various components of soil i.e: organic matter, air, water, etc. play an important role in the effectiveness of the soil and are closely interlinked .For assured yields it is necessary to ensure that this delicate chain of components is not disturbed. Seems a daunting task? Does it mean that one has to move around measuring the pH, moisture, microbial count every time one wants to plant something?

Well it’s not as big a task as it seems to be. The best way to learn is to experiment and observe and understand. So what do we do? Where do we start? Hey! Just take care and pamper the microbes and they will look after the rest of the work and all the nitty gritties for you. Feed them rich organic food, keep them cool and well aerated and leave them to do their work in peace. They are excellent workers at no extra cost.

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