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Does Fertilizer Strength Affect the Growth of Brassica rapa

I had posted this information earlier, but accidentally deleted it. So I am going to try again, because I am grateful for Fast Plants. The above title was chosen by my child for a science fair project that was just completed. My child, in working with this wonderful species, now has a greater respect for plants, the scientific method, and learning for the sake of learning. I credit the ease of use of Fast Plants for capturing my child’s attention and motivating them to follow the project through to the end. The experiment was designed to measure the effects of differing strengths of a standard fertilizer on Fast Plants. The standard fertilizer used was Schulz’ Plant Food (10-15-10). There was no rhyme or reason in choosing this fertilizer, it was the first seen on a shelf of ”common” fertilizers at the garden center. Populations were set up to grow in the following nutrient solutions, no fertilizer (water), ½ strength, standard, 2x strength, and 3x strength. For 20 days, simple measurements were taken and analyzed.

During the course of 20 days, the daily height (cm) of each individual was measured and recorded. This allowed for my child to easily compute the Average Daily Height (cm) for individuals in a population. A growth curve was then created from this which led to some great visual material for the display board. Additionally, the Average Height (cm) for a population was calculated from the final height recorded on Day 20. By comparing the average height of the different fertilizer populations, some good conclusions on growth could be made. The number of flowers (open buds) per individual was also noted and recorded. By using the final flower count, the Average Number of Flowers per population was ascertained and the numerical data compared. On Day 22, a random selection of individuals growing in a particular nutrient solution were removed from their pots and weighed on a balance scale. Their weight became the Total Weight (g). Next, the roots from these individuals were removed and weighed as a group. This became the Total Root Weight (g). Total Shoot Weight (g) was obtained by subtracting the root weight from the total weight. This simple data collection led to basic computations that allowed for my child to better refine their conclusion. They were Average Individual Weight (g), Average Individual Root Weight (g), Average Individual Shoot Weight (g), Percentage Root (average root weight/average weight), and Percentage Shoot (average shoot weight/average weight). In addition to the measured data, leaf color and size were noted and recorded. Though not measured numerically, the visible observations led to some loose interpretations on how the different strengths of fertilizer were affecting their respective plants. The results of the experiment can be found below.

*As the strength of fertilizer increased from a solution containing no nutrients (water) to a solution 3x the standard, plants showed an increase in the following:

Average Individual Weight (g)

Average Number of Offshoots

visible greenness of leaf

*As the strength of fertilizer increased from a solution containing no nutrients (water) to a solution 2x the standard concentration, plants showed an increase in the following:

height (cm)

number of flowers

Average Individual Weight of Shoots (g)

Average Individual Weight of Roots (g)

Percent Shoot

Percent Root

*3x strength individuals were shorter and had fewer flowers than the standard and 2x individuals. They did have larger, darker leaves and many more buds than any other population that remained unopened. These individuals were also slow-growing. It appeared, according to my child, that these individuals were putting the energy received from the extra macronutrients they were consuming into creating plants rich in flowers; therefore, fruit. The roots in this group began to grow larger again, where the trend had been to grow larger shoots. My child believes that the 3x individuals, being “leafier and fatter” than all the others, needs more roots to be better able to support a heavy shoot. The results allowed for my child to conclude that differing strengths of fertilizer does affect the growth of Brassica rapa.

I would like to express my thanks for this wonderful little plant, the Fast Plant. It has made this required project fun, and more importantly, informational. My child has expressed a desire to continue working with the plant. I would like to see them duplicate their experiment to see if it yields similar results, but just expressing the interest to continue working and learning was a thrill to hear; priceless.

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Comment by Wisconsin Fast Plants Program on February 10, 2010 at 10:26am
Thank you so much for sharing and special thanks for the extra effort it took to do so! Your story captures the essence of what keeps us all motivated as educators of all types--that spark in a learner who is captivated by learning--just as you so beautifully described. How wonderful that you and your child shared this learning experience, too. Thank you again for sharing your experience.



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