Spring.wmf (18300 bytes) Plant Physiology (Biology 327)  - Dr. Stephen G. Saupe;  College of St. Benedict/ St. John's University;  Biology Department; Collegeville, MN  56321; (320) 363 - 2782; (320) 363 - 3202, fax;    ssaupe@csbsju.edu

Mineral Nutrition/Hydroponics

I.  Elemental Composition of Plants

A.  Table 6-1 from Salisbury and Ross.

B.  Conclusions: 

  1. 90+% of plant C, H, O, N;

  2. over 60 different elements have been found in plants including gold, arsenic, mercury, lead and uranium;

  3. certain tissues concentrate elements (i.e., young tissues have higher levels of N, P and K);

  4. similar elemental composition in different species.


II.  Essential Elements

A.  Definition - An element is considered essential if:

  1. required for growth and development;

  2. directly involved in plant metabolism;

  3. an integral constituent of important constituents in the plants;

  4. required for life cycle completion; and 

  5. no other element can substitute for it.

B.  Specifics

C.  Conclusions:  

  1. some elements are required in high concentration (macronutrients), others low (micronutrients);

  2. some supplied from the air (i.e., C and O via CO2), most absorbed by the roots from the soil; 

  3. lot of O and H - shows the importance of water.

D. Functions.
    Check the text (Table 5.3 in Taiz and Zeiger) for a nice summary.  Roughly speaking:

  1. C, H, O, N, and S are required because they are the building blocks of the  molecules of life; 

  2. P, B (Si) involved in energy transfer reactions; 

  3. K, Na, Mg, Ca, Mn, Cl have various functions including maintaining osmotic concentrations and structures of enzymes;

  4. Fe Cu Zn Mo prosthetic groups, electron transfer reactions.


I
II.  Determining nutrient elements.
    Use soil-less techniques.  Julius Sachs first showed could grow plants in solution culture in 1860.  Term hydroponics coined by W.F.Gericke in 1930's (from Greek, hydro = water; ponos = labor).  Many variants of the technique so long as: (1) support plant; (2) supply proper elements; (3) roots receive adequate aeration and moisture.

    The techniques include: (1) solution culture (+/- aeration); (2) nutrient film techniques; (3) aeration systems.

IV.  NPK
    Nitrogen, phosphorus and potassium are usually the most limiting elements because they are required in the highest concentration and are least likely to be supplied in a soil/growth medium in adequate amounts.  Hence the need for fertilizers.  Labels include the form and percent of each; i.e, 14 - 14 -14 means that a fertilizer has 14% nitrogen, 14% phosphorus and 14% potassium.  Fertilizer labels also include micronutrients.

    In class we will see some slides of "The Land" exhibit from Epcot.


V.  Calculating the cost of a fertilizer based on nitrogen content

Comparing Costs of Fertilizers

Brand

Type

N-P-K

Pkg Price ($)

Pkg Wt (kg)

Nitrogen Cost ($/kg)

RaPid Gro

S

23-19-17

1.99

0.227

38.10

Peter's

S

15-13-7

1.19

0.071

Jobe's spikes

C

10-10-4

1.49

0.015

Knox Gelatin

O

15-0-0

0.59

0.028

Miracle-Gro

S

15-30-15

2.19

0.227

Osmocote

C

14-14-14

4.95

0.553

(key:  S=soluble; C=controlled release; O=organic). 

References:

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Last updated:  01/07/2009     � Copyright  by SG Saupe