The effect of Nitrogen based fertilizer on the growth of Saintpaulia Ionantha

Brandy Marshall

Undergraduate – Health Sciences

Tennessee Technological University

Cookeville, TN 38505

6 December 2006

People are often torn over whether or not to use fertilizers on their plants and crops. With the recent price spikes in nitrogen fertilizers and studies concluding that nitrogen might be leaking into drinking water, people are thinking twice about using them. The object of this experiment to test nitrogen based fertilizers to see if they have an effect on plants. For this particular experiment, Saintpaulia Ionantha (African Violets) will be used along with Miracle Grow for house plants. I hypothesize that the fertilizer will have an effect on the plants, causing the ones fertilized to grow larger and faster than the plants not given fertilizer. Variables observed in the experiment included height, number of leaves, and number of flowers for each plant. After all the data had been collected and analyzed, the experiment showed that the plants given nitrogen based fertilizer grew larger than the plants not given fertilizer, therefore the hypothesis was accepted.

Saintpaulia Ionantha, African Violet, fertilizer, Nitrate, Ammonium, Nitrogen

            As we all know, the world population grows everyday, and everyday more and more emphasis is being placed on money and damage to the environment. Fertilizers of any sort can become very expensive, especially nitrogen based ones. That is one of the reasons people today ask if fertilizer really works or not. To the average person who just fertilizes their flower garden, cost usually is not a major concern. These people only want their flowers to grow large and beautiful. On the other hand, to people who own farms or nurseries and depend on the plants for a living, cost is a major concern. 

There have also been a few studies recently concerning the safety of using nitrogen based fertilizers. Many times when the nitrogen is in the nitrate form, the crop is unable to utilize the entire amount of fertilizer it is given. This leaves the remaining nitrogen to run with water from the soil into groundwater systems or drainage systems (Jiusheng et al, 2005).

            “The big three nutrients needed by plants are nitrogen, phosphorus, and potassium” (Reich 2002). For this experiment, nitrogen fertilizer will be the fertilizer tested. Nitrogen can be given to plants in many different forms including organic fertilizer (animal manure, composts, or plant residues), NH4+ and NO3 ˉ (Heeb et al 2005). The fertilizer used for this experiment is 24% Nitrogen, containing 3.5% ammoniacal nitrogen and 20.5% urea nitrogen. Many experiments have been conducted to test the effects of nitrogen based fertilizers and conclude that plants given nitrogen fertilizer will grow larger and faster than the same type of plant not given fertilizer. One, for example, tested the growth rate of flowers based on number of times a fertilizer was given and whether or not the plants were in sunlight. It was concluded that the plants given the most fertilizer, grew the largest in sun and shade (Stafne et al, 2005).

One problem encountered with fertilizer though is that it only stays in the soil for a few days, then has to be reapplied. Urea’s half life, for example, is only about six days immediately following transplanting and then falls to only three days (Sheehy et al 2005). This fact once again raises the question, are fertilizers worth the extra money and possible harm to the environment?

The objective of the experiment is to show effects of nitrogen based fertilizers in hopes of answering the question do fertilizers really work. If the null hypothesis is correct, plants given the fertilizer mixture will not grow larger than plants given no fertilizer. If the hypothesis is correct, plants given fertilizer will grow larger than the plants not given fertilizer and it could be said that yes, fertilizers do work and are worth purchasing.

Materials for this experiment are all easily acquired. The materials include 6 plants, 6 pots, potting soil, nitrogen fertilizer (Miracle grow for house plants was used in this experiment), water and a plastic container for the fertilizer mixture. This experiment can be found by visiting Science Buddies.com (Powers, 2006).The original experiment called for eight plants, but due to time and budget issues, only six were used for this experiment.

To begin this experiment, one must first acquire all materials needed. Then, measure equal amounts of potting soil into each of the six pots. Moisten the soil with equal amounts of water, and label 3 pots with “fertilizer” (the treatment group) and three pots with “no fertilizer” (the control group). Now, plant one plant in each of the pots and place near a sunny window. Mix a container of fertilizer according to instructions on the package. Water each plant once a day, and give the fertilizer group the fertilizer mixture once a week. Record the observations in a notebook once a week. Observations should include stem height, number of leaves and number of flowers.

The experiment is being conducted in my apartment. The plants have access to sunlight, and I have easy access to the plants for observations and watering. At the end of the experiment, the values recorded were used to compare the sets of plants and determine which set grew the most as outlined by the original procedure. Graphs and tables were then constructed using Microsoft Excel of the comparison.

            At the conclusion of the experiment, one can see that the group watered with nitrogen fertilizer once a week grew larger than the group given only water. Table 1 shows the set up of the experiment.

Table 1: Set-up of plants used in the experiment.

 Figure 1 shows the height in centimeters each plant grew during the eight week period. Plants 1 through 3 were the treatment given fertilizer and plants 4 through 6 were the control group only given water. The treatment group grew an average of 4.0 cm while the control group only grew an average of 2.6 cm.

Figure 1: Height grown in centimeters of each plant over an eight week period.

Figure 2 shows the number of new leaves each plant grew during the same eight week period. It is also evident in figure 2 that the treatment group given fertilizer made more progress than the control group without fertilizer. The treatment group grew an average of 6.7 leaves while the control group grew an average of 4 leaves.

Figure 2: News leaves grown by each plant over an eight week period.

Figure 3 shows the number of new flowers each plant produced during the experiment. The treatment group grew and average of 8.3 new flowers while the control group grew and average of 4.7 leaves. After looking at the numbers produced by the experiment, one can see that the treatment group given the fertilizer grew larger than the control group, accepting the hypothesis.

Figure 3: Number of new flowers grown by each plant over and eight week period.

            Nitrogen is required for all phases of growth and development in plants (Jensen 2005). The purpose of this study was to test the effect nitrogen based fertilizers had on plants, and it was hypothesized that the fertilizer would make the plants grow larger. As the results show, the hypothesis was accepted. The treatment group that was given fertilizer grew larger than the control group not given fertilizer. These results agree with two earlier experiments done by Heeb and Stafne that both said application of nitrogen increases plant size.

            There were a few things to take into consideration about this experiment. First, nitrogen dosage plays a large roll in the effect of these fertilizers. Many experiments have been done in the past to determine the right levels of nitrogen plants need to get maximum growth. It is very important to know how much fertilizer to use because if too much is applied, the fertilizer does not work (Ashraf et al 2006). For the fertilizer used in this experiment, tests had already been conducted and a maximum amount, called the optimum N rate, was stated on the container (Olfs et al 2005). The plants were only given dosages proven to be safe and successful.

            Another fact that should be taken into consideration is that nitrogen fertilizers can affect other components in the soil. According to a study done on the effect of nitrogen fertilizer on the transformation of phosphorus, the addition of nitrogen to the soil transformed the phosphorus also present in the soil into a more absorbable substance (Du Zhen-Yu et al 2005). This could be another possible explanation as to how nitrogen fertilizers make plants grow larger. 

            One last point to take into consideration is how the fertilizer is applied. Some fertilizers give one big dose of nitrogen all at once, while others are controlled-release fertilizers (Birrenot et al 2005). The application of the fertilizer could play an important role in how well it works, so an experiment like this could possibly be done in the future to help clarify the results. 

·        For maximum growth most soils need to be fertilized

·        Nitrogen based fertilizer makes plants grow larger

·        Too much or too little fertilizer has no effect

            Further research should be done with this experiment looking at all components of the fertilizer, not just the nitrogen. One might also look at the application of the fertilizer. Studies such as these might give a better indication as to why the fertilizer works.

The author would like to thank Elizabeth Yokley for her assistance in gathering the data used for this experiment.

Ashraf, M., Oasim Ali and Eui Shik Rha. 2006. Effect of Varying Regimes on Growth, Seed Yield, and Nutrient Accunnulation in Isabgol. Journal of Plant Nutrition 29:535-542.

Birrenkott, Brian A., Joseph L. Craig and George R. McVey. 2005. A leach collection system to track the release of nitrogen from controlled-release fertilizers in container ornamentals. Hortscience 40:1887-1891.

Du Zhen-Yu, Zhou-Jian-Min, Wang Huo-Yan, Du chang-Wen and Chen Xiao-Qin. 2005. Effect of nitrogen fertilizers on movement and transformation of phosphorus in an acid soil. Pedosphere 15:424-431.

Heeb, Anuscka, Bengt Lundegardh, Tom Ericsson and Geoffrey P. Savage. 2005. Effects of nitrate-, ammonium-, and organic-nitrogen-based fertilizers on growth and yield of tomatoes. Journal of Plant Nutrition and Soil Science 168:123-129.

Jensen, Erika. 2005. Feed your garden. Organic Gardening 52:38-41.

Jiusheng, Li, Bei Li,Minjie Rao. 2005. Spatial and temporal distributions of nitrogen and crp yield as affected by nonuniformity of sprinkler fertigation. Agricultural Water Management 76: 160-180.

Olfs, Hans-Werner, Klaus Blamkenau, Frank Brentrup, Jorg Jasper, Axel Link and Joachim Lammel. 2005. Sooil- and plant-based nitrogen-fertilizer recommendations in arble farming. Journal of Plant Nutrition and Soil Science. 168:414-431.

Powers, La Ne. 2006. Growing, Growing, Gone! An Experiment on Nitrogen Fertilizers. Science Buddies <http://www.sciencebuddies.org/mentoring/project_ideas /PlantBio_p012.shtml>.

Reich, Lee. 2002. Fertilizers. Horticulture.99:94-98.

Sheehy, John E., P.L. Mitchell, Guy Kirk and Anaida Ferrer. 2005. Can smarter nitrogen fertilizer be designed? Matching nitrogen supply to crop requirements at high yields using a simple model. Field Crop Research 94:54-66.

Stafne, R.A., A.E. Einert and G.I. Kilngaman. 2005 Fertilizer Applications on Establishment and Growth of Three Groundcover Species in Sun and Shade. Journal of Environmental Horticulture 23: 157-161.

The effect of Nitrogen based fertilizer on the growth of

Saintpaulia Ionantha (African Violets)

Sample Taken by: Brandy Marshall                   Date: 10-11-2006

                                     Location: ____Cookeville, TN_____                 

Signature: _________________________    Date: ________________________