David Janssen

                                                                                                                                   Botany

                                                                                                                                  10/15/01

Difference In Duckweed Growth Rates Between Plants Grown In Macro Nutrient Solution

verses Macro Plus Micro Nutrient Solution

Introduction:

    Gardening over the years has shown me that nitrogen, phosphorus and potassium, called macro nutrients, can increase the yields from a garden substantially. I also noticed that when a garden was fertilized with substances recognized as Micro nutrients, boron, iron, copper etc , along with a balanced macro nutrient fertilizer, the plants in the garden looked healthier.  This led me to believe that the common practice of adding only macro nutrient fertilizers to gardens may not be the best way to maximize the potential harvest and gardeners should be more aware of the need for a more balanced and complete spectrum of nutrients a plant will need to grow more productivity.

     In this study I tested the hypothesis that duckweed grown in macro plus micro nutrient fertilizer will be more productive than duckweed grown with only macro nutrient fertilizer.

Methods:

     I used eight Styrofoam bowls and filled four of them with a solution of two-thirds distilled water and one-third Optimara® Violent Food mixed with distilled water according to the directions on the box.  This fertilizer contains 14 percent total nitrogen, twelve percent available phosphate and 14 percent soluble potash (potassium). I  labeled these bowls macro fertilizer, numbered 1 thru 4.  I filled the second four bowls with two thirds distilled water and one third

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Miracle-Gro® African Violent Food  mixed with distilled water to twice the concentration listed in the directions on the bottle.  This was to insure that all bowls contained approximately the same macro nutrient percentages.  This fertilizer was mixed to contain 14 percent total nitrogen, 14 percent available phosphorus and 14 percent soluble potash (potassium) along with the micro nutrients 0.04 percent boron, 0.1 percent copper going to percent higher 0.16 percent manganese and 0.1 percent zinc. I  labeled these bowls macro plus micro fertilizer, numbered 5 thru 8.

     Sixteen healthy duckweed plants were added to each of the 8 bowls. Bowls were then placed in the greenhouse on Western New Mexico University’s campus.  The bowls were monitored

regularly and the fluid level maintained by adding distilled water when needed. The duckweed in

each bowl was counted every seventh day for four weeks and results recorded and a graph of the

results made.

Results:

     It became very apparent, when examining the graph, that duckweed grown in macro plus micro nutrient fertilizer was more productive than the fertilizer containing only macro nutrients.  By the fifth week the bowls, 1 thru 4, containing only macro nutrients did not contain any living

duckweed, while bowls, 5 thru 8, containing the macro plus micro nutrient fertilizer contained an

average of 306 duckweed plants per bowl.

Discussion:

    The dramatic results of this study strongly support my hypothesis that duckweed grown with a

macro plus micro nutrient fertilizer will be more productive than those grown with a macro

nutrient only fertilizer  The attached graph shows clearly that during the first two weeks there was little difference between the macro only group and the macro plus Micro group in productivity. The third and fourth weeks however showed a dramatic die off of all duckweed in the macro nutrient only fertilizer group, while the macro plus micro nutrient fertilizer group showed spectacular productivity during this period.        

      The results of this study raised many questions about the common practice of using only

macro nutrient fertilizers on food crops to increase productivity.  Does the prolong use of this type of fertilizers cause plants to slowly drain micro nutrients from the soil and eventually  lead to the collapse of the fertility of soils and their continuing ability to support plant life. If so, shouldn’t this study at least cause some concern.  History has many stories of civilizations that collapsed after the land they grew food crops on would no longer support those crops. Was this part of the cause of their collapse?

      If I were to repeat this experiment I would have liked to add a control group that used only

distilled water or possibly at another group with a fertilizer containing a more complete micro

nutrient recipe to see to what degree these additional groups had different results, in productivity,

from the fertilizers used in this study.

     The outcome of this study shows that further study is needed to determine what nutrients are

required for optimal productivity and the amounts of the different macro and micro nutrients

needed to produce the best results.  I would be pleased if some future botany class would continue this research and answer these questions.