Wednesday, September 15, 2010

Plant Growth : Nutrients

Essential elements
Carbon ( C ) , Hydrogen ( H ) ,& Oxygen ( O).

Essential elements ( Arnon and Stout, 1939) :
-        A plant must be unable to complete its life cycle in the absence of the mineral element.
-        The function of the element must not be replaceable by another mineral element.
-        The element must be directly involved in plant metabolism.


Macronutrients ( 大量元素):
Nitrogen
(  N ) , Phosphorus( P ) , Potassium( K ), Calcium( Ca ) , Magnesium( Mg ) ,&  Sulfur( S ).         

Macronutrients are consumed in large quantities.  They are present in plant tissue in quantities from 0.2% - 4%.



Micronutrients ( 量元素 ) ( Trace elements ) :
Chlorine ( Cl ) , Iron ( Fe ) , Manganese ( Mn ) , Boron ( B ) , Zinc ( Zn ) , Copper ( Cu ) , Molybdenum ( Mo ) , Sodium ( Na ) ,& Nickel ( Ni ).  

Micronutrients are present in plant tissue in small quantities.


Beneficial Elements :
Silicone ( Si ) ,&  Cobalt ( Co ).   

Beneficial elements are those that  :
-        can compensate for toxic effects of other elements or
-        may replace mineral nutrients in some other less specific function e.g. the maintenance of osmotic pressure.

The omission of beneficial nutrients in commercial production could mean that plants are not being grown to their optimum genetic potential but are merely produced at a subsistence level.

The beneficial elements have not been deemed essential for all plants but may be essential for some.

 
e.g. Cobalt is essential for nitrogen fixation in legumes. It may also inhibit ethylene formation ( Samimy, 1978 ) and extend the life of cut roses ( Venkatarayappa et al., 1980 ).

e.g. Silicon is deposited in cell walls, has been found to improve heat and drought tolerance and increase resistance to insects and fungal infections. Silicon can help compensate for toxic levels of manganese, iron, phosphorus and aluminum as well as zinc deficiency.
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