Nutrition is vital to plant survival. In the wild, wild wilderness, the soil is sometimes busting at its seams with natural nutrients. In nature, these are provided by decomposing plants releasing their nutrients into the soil. When man started artificially growing plants, he realized that they quickly depleted the natural supply of nutrients required for the plants to grow.
Man then thought of a solution to the problem. He decided to replenish the soil synthetically. These added chemicals eventually were called fertilizer. It came in all shapes and sizes, ranging from cow manure to fertilizer pellets, containing raw chemicals. In several centuries of cultivation, humans have come a long way, but the work is not complete.
Our researchers questioned whether the current amount of chemicals being widely applied was the best ration for the plants. To begin experimenting with how plants react to certain chemicals, our scientists obtained an ideal species of plants for experimentation. These test plants are known as Brassica Rappa; they are also dubbed Wisconsin Fast Plants. The investigators set up a watering system, which watered the plants through a series of wicks. Then, they placed varied numbers of fertilizer pellets into each plant’s soil. We hypothesized that the greater the number of pellets, the better the plants would grow.
Brassica Rappa was an ideal specimen because they grew quickly; it was thus easy to observe the effects of our variables on them. Varying amounts of “fertilizer pellets” were inserted into each quad. A quad is a Styrofoam “pot” which contains three individual cells, each containing one plant. Our control was the quad with no pellets, because the independent variable (fertilizer pellets) were not applied to it. Then, they filled three other quads, one with zero pellets, one with two pellets, and one with six pellets. The amount of pellets was our independent variable. Our researchers’ goal was to observe how the independent variable effected each of the dependent variables. In other words, they were trying to find out what the effect of the fertilizer was on the fast plants.
There are three main nutrients that are essential to plants. One of these is Nitrogen. Nitrogen is vital in the growth of leaves, and photosynthesis. If a plant is Nitrogen deficient, its leaves will start to turn yellow, and it will have stunted growth. In our experiment, the plants with zero or two fertilizer pellets were noticeably smaller than the plants with the recommended four pellets. These plants also had white areas on the edges of the leaves. It was unclear to us if this was caused by a lack of Nitrogen, or if they are dead areas resulting from a Phosphorus deficiency.
The reason that they don’t know if the white edges are from Nitrogen or Phosphorus is because our pellets contained Nitrogen (N), Phosphorus (P), and Potassium (K). Thus, they could only observe how all three of these nutrients effect the plants, when they are applied in different ratios with each other. Phosphorus is also crucial to plants. It is particularly needed when the plant is in its early developing stages. Insufficient Phosphorus causes: stunted growth, and purplish-red leaves. The Phosphorus deficiency showed up in our plants within the first week. Plants without enough fertilizer were smaller, and had purple leaves. Remarkably, the plants with enough fertilizer were growing rapidly, and had dark green leaves.
The final main nutrient is Potassium. Although the exact reason for Potassium in plants is unknown, there are several side effects in plants with insufficient Potassium. In a plant that doesn’t have enough Potassium, the rate of photosynthesis goes down and the respiration rate goes up. This causes the supply of carbohydrates to decrease. Potassium is also needed for protein synthesis, and efficient water management.
The fertilizer pellets which they used as our independent variable contain necessary nutrients for the plants’ survival. In each quad, they applied varying numbers of pellets. They put zero pellets in our control, two pellets in our less than recommended quad, four pellets in the recommended quad, and six pellets in our above recommended quad. These pellets are made up of 20% Nitrogen (N), 20% Phosphoric Acid (P2O5), 20% soluble Potash (K2O), and 40% of varying amounts of Potassium, Magnesium, Sulfur, Iron, Chlorine, Copper, Manganese, and Zinc (Understanding the Environment, 4). The independent variable was only to be applied once, and that was at the time of the planting (at a depth of 4 mm). For the duration of the plants’ lives, they will continue to be effected by the difference in fertilizer at the beginning. In order to see the results, they observed many things.
There are several quantitative dependent variables that they observe in our plants. All of these are observed every class period (Monday, Tuesday, Thursday), and are recorded by the “day in the life of the plant”, which is how many days it has been since they planted the seeds. One of these is the leaf size. They measure the leaf size from the stem to the very tip of the leaf. This measurement thus includes all parts of the leaves. Another quantitative dependent variable is the most number of leaves. This is measured by counting the number of leaves on the plant which has the most. For our purposes, a leaf is defined as anything sprouting out from the stem which is not a cotyledon or a flower bud. An additional quantitative dependent variable is the number of flower buds. This is recorded by counting the total number of flower buds in a quad. A bud is considered a bud when the tip extends at least a millimeter from the stem. Our final quantitative dependent variable is plant height. For the height of the plant, they measure from the top of the soil to the very tip of the plant. The tip is defined as the highest, natural position of the plant. If a leaf is bending under its own weight, they measure from the top of the arc. For our qualitative dependent variable, they are observing the color of the leaves. If at least three millimeters of a plant leaf are a color, that color is observed in the observation. For example, a plant could be green, yellow, and purple at the same time. There is one exception. If the longest leaf is not three millimeters, they observe the color within one millimeter.
Before the experiment actually began, they predicted the effect that the independent variable would have on the dependent variable. They predicted that the plants with more fertilizer would be taller, have more leaves, have larger leaves, and have more buds. They thought that the zero pellets would have the worst (most undesirable) effects. The second to worst would be the one with two pellets. The best would be four pellets. And the second best would be the six pellets. They also predicted that the plants with zero pellets would be yellow, the plants with two pellets would be yellow green, the plants with four pellets would be dark green, and the plants with six pellets would be light green (Plant Nutrition).
Results of the experiment were mixed. For some unknown reason, our plants grew very little. This could have been caused by the treatment, or by a limitation of our experiment. Our researchers did the best they could with the less than par performance of our plants.
In their first dependent variable, plant height, they saw the expected results. The control hardly grew at all, and died just after germination. They suspect that this is because the soil used didn't have enough nutrients to support the plants. From these results, one could conclude that Brassica Rappa need more nutrients than are naturally found in this type of soil.
The quad that contained two pellets had slightly better results. After an early mishap, the young scientists replanted the quad, and observed much better results than in the first go around. This quad then had some remarkable results. In two of the cells, the plants grew rapidly, up to a point. As they matured, they grew true leaves and flower buds. After day thirteen, it spontaneously stopped growing. The researchers determined that this was because they had already absorbed all of the available nutrients out of the soil. This could be true, but it may have been another, unknown factor, such as bugs or mice.
The quad with four pellets had the best results of an individual plant. They all grew rapidly, up until where their flower buds appeared. Then, their upward growth stopped almost completely, and their development of leaves, flowers, and seed pods. Once again, our researchers concluded that the soil must have run out of nutrients; but there could have been something outside of our visual field that was stunting the plants' growth.
The quad with six pellets had the most consistent growth. All of the cells in the quad grew, some with more than one plant in them. This was exactly what our panel of expert young scientists had hypothesized would happen. These plants grew as rapidly as the fastest growing four-pellet-plant. But they too also stopped growing right as they were developing flower buds. It is curious how all of the treaded quads stopped growing at the point where the buds came out. In the six-pellet-plant, they observed algae growing on the watering system. This was expected, because the soil was so rich, and the researchers tried to scrape the algae as it appeared. This probably helped a little, but the fact is that algae could have been small enough to pass unnoticed under the course of observations.
The other four dependent variables, leaf length, leaf width, number of leaves, and leaf color, followed the result pattern of the plant height. The quads' quality increased as the number of pellets increased. The only exception was the plant color, which must be explained in deeper depth, because it is a qualitative, not quantitative, observation.
Although the apparent results in plant color were the same, the color can't be recorded so easily. For example, a plant with brown spots, but mostly dark green leaves could be healthier than a plant with all light green leaves. Also, since colors can be different on different leaves within the same plant, it can be hard to classify each plant as healthy or non-healthy.
If the researchers had been able to observe the F1 generation, they would have observed another dependent variable. This would have been the percentage of plants that germinated. Since none of the original plants reached maturity, they were unable to reproduce. Thus, this dependent variable was zero percent for every quad.
After the experiments were completed, our scientists compared their results with the results of fellow colleagues at Dowling High School. They found that their results were similar, with the exception that the other groups’ plants did not stop growing at the flowering stage. In fact, some of the other teams were even able to observe an F1 generation. Their results of before flowers emerged concurred with our researcher’s observations. They found that the more fertilizer they placed in the quad, the better the plant’s growth; also, the greater the amount of fertilizer, the greater the amount of algae.
The scientists involved in the nutrition testing of Brassica Rappa in Period 7 had many limitations which may have prevented accurate results. One of the limitations that they encountered was a problem with the amount of fertilizer inserted. Since they didn’t fill all of quads and cells with the same amount of soil, it could have prevented all of the cells from growing with an equal chance for survival. This also created another variable, which was not accounted for. Another limitation of the researchers was that they didn’t plant all of the seeds at exactly the same depth. This also created an unexpected variable, which makes it very difficult to interpret why the differences between the plants occurred.
Algae was also a big problem for the scientists. They grew in large quantities in the quads with greater quantities of fertilizer. The researchers didn’t realize that this algae growth would effect the plants until late in the experiment, so it continued to grow rapidly, and may have smothered the plants’ growth. Another effect of the algae was that it used up the nutrients and was, in effect, taking away the independent variable.
Also, since their plants did not reach a period where they could reproduce, our scientists were unable to take observations of the F1 generation. It would have been interesting for them to see how the fertilizer effected the plants’ reproduction.
If this experiment is performed again, the scientists should be aware of these things, and take preventative measures. In conclusion, the fertilizer did help the plants to grow, just as our researchers hypothesized. Farmers should be careful not to over-fertilize, as it may lead to tremendous algae growth, which may crowd the land, and smother the vegetation.
Works Cited
“Understanding the Environment.” Carolina Biological Supply. Available online at: April 27, 2003.
“Plant Nutrition.” Newfound and Labrador Agriculture. Available online at: April 28, 2003.
Carolina Biological, 2003. Nutrition. Carolina Biological Supply [On-Line], April 13, 2003. Available:
Columbia Electronic Encyclopedia, 2000. Fertilizer. Columbia University Press [On-Line], April 13, 2003. Available: