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ESSENTIAL ELEMENTS, MOBILITY AND pH EFFECT
essential element - an element required by plants for normal growth, development and completion of
                                its life cycle, and which cannot be substituted for by otherchemical compounds.

17 ELEMENTS ARE REQUIRED BY PLANTS
 3 supplied naturally by air and water - comprise the bulk of the plant 
    C, H, 0 
 6 macronutrients - required at 0.1 to 6% of the dry weight of plants 
    N, P, K, S, Ca, Mg
 8 micronutrients - required at 1 to 300 ppm of the dry weight of plants 
    Fe, Zn, Cu, Mo, B, Mn, Cl, Ni
    Cl and Ni are ubiquitous - hence, will not be addressed in detail 

The essential elements can be easily remembered by a catch phrase such as 
C. HOPKiNSCaFe, CuB, Mn, C.l. MoNiZnsky, Mgr
 

NUTRIENT MOBILITY
Two directions of movement in plants
1) acropetal - means towards the apex; transport up in the xylem 
2) basipetal - means towards the base; transport down in the phloem 

Two classifications of nutrient mobility
1) mobile - moves both up and down the plant by both acropetal and basipetal  transport (in both 
                  the xylem and phloem).
                - deficiency appears on older leaves first. 
    N, P, K, Mg, S
2) immobile - moves up the plant by only acropetal (in the xylem) transport. 
                    - deficiency appears on new leaves first. 
    Ca, Fe, Zn, Mo, B, Cu, Mn
 

EFFECT OF pH
The pH determines solubility in the soil
1) more available at low pH (below 5.5), and less available at high pH.
    Fe, Zn, Cu, Mn, B
2) more available at high pH (above 6.5), and less available at low pH.
    N, K, Mg, Ca, S, Mo 
3) more available at intermediate pH (6-7) 
    P  

Ideal pH: slightly acid:
a) around 6.5 for field soil 
b) around 5.5-6.0 for artificial growing media made with peat moss or composted bark