Molly,+Kate,+Nate

Nate Giess, Molly Micou, and Kate Westenberg 5/30/11

TAN The Effect of Soil Composition on Plant Growth Soil is a necessary part of not only human lives but the lives of other animals as well (1). The correct composition, or the different sediments that make up soil, provides a healthy amount of nutrients and controls the amount of water the soil can retain (1). This is important to plants because in order for plant growth to occur, a plant must have glucose and water. By testing the best soil texture, farmers can find out the best place to grow healthy crops instead of buying a portion of land that would be no good to grow crops necessary to earn a profit. This directly affects communities because a farmer with crops that do not grow well means communities, both near and far, will have no source of food. Soil is made primarily of four components: sediment, humus, water, and air (1). The texture of soil, which describes the sediment in the soil, is classified into categories based on the percentages of clay, sand, and silt in the soil (1). Clay is made of many tiny pores and is very smooth. Because of the number of pores it has, clay has a high porosity, however, the size of the pores makes it difficult for water to be released, thus making the clay impermeable (5). If the water cannot be released fast enough, it pools, eventually drowning the plant. Sand is between 2 mm and .06 mm in size, is coarse, and often angular. The pores are large and well connected, so water can travel through it easily; however, the water passes through the sand so quickly that moisture is not retained. If the water is released so fast by the soil that the plant does not have time to utilize the moisture, the plant shrivels up and dies. Also, water that drains from sand can sometimes leach the nutrients out of the soil, thus making the plant experience malnutrition. Since neither pure sand nor pure clay are ideal for a plant, the plants will probably prosper the most when there is some of each. The sand would let water flow through to the plant and past it so it doesn't drown but also the clay would hold it there just enough so the soil can absorb some of the water in and not completely miss the water. Organic material, in this case, compost, is also essential, for it provides the nutrients for the plant, as well as improves the soil's ability to retain water (1). All three of these components are important, but only in certain amounts. Soil moisture depends on the permeability of the soil, thus the moisture of the soil, and the ability for the beans to grow, will depend on the composition of the soil (2). To make sure accurate results are obtained, the amount of water, sun, and temperature for each plant, as well as the plant itself, will remain constant. The best soil will ultimately be the composition that provides the most nutrients and moisture for the plant, as witnessed in the plant's growth. A fast growing plant is considered good, as it makes pest establishment difficult (6). Radishes, a fast germinating and growing plant will be tested in this experiment. Radishes will grow in almost any soil, so long as they obtain enough moisture and nutrients (4). The hypothesis for this experiment is that **the best soil composition for stimulating vertical growth radishes is a fifty-fifty ratio of sand to clay, with a light amount of humus.**
 * Introduction**
 * Materials & Methods**

1) Prepare all 5 of the soil mixtures.
 * || Sand || Clay ||
 * Composition 1 || 100% || 0% ||
 * Composition 2 || 75% || 25% ||
 * Composition 3 || 50% || 50% ||
 * Composition 4 || 25% || 75% ||
 * Composition 5 || 0% || 100% ||

2) For each soil type, put 200 cm3 into each of the 30 pots roughly the size of a Styrofoam cup.

3) Add the proper amount of organic material to each pot. The first 10 will have (0 cm3 organic material), the second 10 will have (7.4 cm3 organic material) and the last 10 will have (14.79 cm3 organic material). You should now have these 15 different soils. (0 cm3) ||   || Little Organic Material  (7.4 cm3) ||   || A lot of Organic Material  (14. 79 cm3) ||  ||
 * No Organic Material
 * Sand || Clay || Sand || Clay || Sand || Clay ||
 * 100% || 0% || 100% || 0% || 100% || 0% ||
 * 75% || 25% || 75% || 25% || 75% || 25% ||
 * 50% || 50% || 50% || 50% || 50% || 50% ||
 * 25% || 75% || 25% || 75% || 25% || 75% ||
 * 0% || 100% || 0% || 100% || 0% || 100% ||

4) Plant a radish seed on the surface of each pot.

5) Make sure the same amount of water is added to each of the plants each day, and that sunlight, temperature, and humidity are always the same for all of the samples (this can be done by simply keeping them in the same place). For the water, use a graduated cylinder, adding 15 cm3 per day. Set up the florescent light so that all plants receive full sunlight. Also set a timer so that the florescent light is on from 7am to 7pm, and is off otherwise. Keep the humidity the same by keeping all of the plants in one closed-off room and the temperature constant with a thermostat.

6) Use a ruler to measure the top most point of the plant every day. Use millimeters for units. Do not pull the plant up higher than is natural, as this can pull it out of the soil. Simply measure from the base of the plant to the highest natural point.

Note: It is advised to take a set of practice data, using any fast-growing plant, before following through with the procedure. In this experiment, beans were used as practice data.


 * Results**

Light Humus (Height in mm):

100% C || Radishes 75% C || Radishes 50% C || Radishes 25% C || Radishes 0% C ||
 * Date || Radishes
 * 5/10 || 0,3 || 3,1 || 7,5 || 2,6 || 6,8 ||
 * 5/11 || 0,2 || 4,0 || 23,25 || 17,26 || 13,19 ||
 * 5/12 || 0,13 || 4,0 || 28,36 || 21,32 || 35,30 ||
 * 5/13 || 0,26 || 21,0 || 41,44 || 32,47 || 46,37 ||
 * 5/14 || 0,31 || 24,0 || 43, 51 || 42,61 || 59,62 ||
 * 5/15 || 0,43 || 33,18 || 46,51 || 34,70 || 63,51 ||

No Humus (Height in mm):

100% C || Radishes 75% C || Radishes 50% C || Radishes 25% C || Radishes 0% C ||
 * Date || Radishes
 * 5/10 || 0,6 || 1,3 || 2,4 || 1,17 || 6,3 ||
 * 5/11 || 17,2 || 0,5 || 20,11 || 6,31 || 17,16 ||
 * 5/12 || 27,0 || 0,3 || 30,25 || 23,41 || 27,24 ||
 * 5/13 || 42,0 || 0,9 || 49,41 || 36,52 || 32,41 ||
 * 5/14 || 47,0 || 0,9 || 59,47 || 40,57 || 35,47 ||
 * 5/15 || 52,0 || 0,22 || 70,54 || 40,62 || 35,55 ||

Heavy Humus (Height in mm):

100% C || Radishes 75% C || Radishes 50% C || Radishes 25% C || Radishes 0% C ||
 * Date || Radishes
 * 5/10 || 8,2 || 11,15 || 9,10 || 4,17 || 9,15 ||
 * 5/11 || 35,21 || 19,22 || 35,24 || 12,31 || 27,37 ||
 * 5/12 || 34,21 || 9,9 || 47,9 || 25,46 || 32,54 ||
 * 5/13 || 52,42 || 31,41 || 64,32 || 33,61 || 45,72 ||
 * 5/14 || 57,41 || 36,50 || 71,42 || 36,68 || 54,84 ||
 * 5/15 || 70,51 || 41,56 || 80,43 || 40,71 || 61,82 ||

Graph 1: As the amount of humus given to the soil increases, plant growth exceeds at a faster rate. On average, the difference between the rate of growths, heavy humus compared to light and none, is about ten millimeters. The heavy humus soil appears to have increased plant growth by about 60%. On day one, growth for the heavy humus plants was, on average, ten millimeters, while growth for the light/none humus plants was about four millimeters. Thus, the difference in height was six millimeters. 6/10= .6, or about a 60% increase with the addition of heavy humus. All three lines seem to increase and decrease in synchronization, only the heavy humus growth starts out as much greater than that of the little to none humus growth. This, again, is supported with the fact that the difference in heights between the different amounts of humus remains constant. Graph 2: As the amount of sand in the soil increases, plant growth increases. Vertical plant growth appeared the strongest in the 0:100 clay: sand composition. On average, the difference in height between 100% sand and the other compositions was about ten millimeters. The one exception to this was the 75:25, clay: sand composition, whose difference in height with the 0:100 clay: sand composition was about twenty five millimeters. Similarly to the first graph, the rest of the soil compositions seem to fluctuate in unison with the 0: 100 clay: sand composition. An exception to this is the 25:75, clay: sand composition, which seemed to grow faster on some days than the 100% sand composition witnessed. Overall, the first graph shows that across the board, the heavy humus mixes caused the most plant growth. Regardless of clay: sand ratio, the soil with heavy humus had the most plant growth. However, the light and no humus compositions were almost exactly the same in plant growth, which was unexpected. The last graph shows that 0% clay was the most successful soil, and that 75% clay was the least successful. 50%, 25%, and 100% clay were all very similar in plant height. The final two graphs, illustrating the daily average plant growth for different amounts of humus and the daily average plat growth for different soil compositions, together suggest that very sandy soils with lots of organic material are best for growing radishes, which does not concur with the hypothesis. The hypothesis was that a 50/50 mix of clay and sand with light humus would be most successful, and neither the humus level or soil type was shown to be the correct prediction. But, interestingly, on both graphs, with one exception, the lines are very similar, showing that if the soil isn’t pure sand, it isn’t very important what the soil composition is. The one exception to this is the 25% sand soil, which across the board for humus type did not grow as well as any of the other soils. This could well be because of the fact that that specific soil was on the outside of the testing area, which may have caused it to get less light than the other plants. This would have caused the slightly stunted growth. However, on the whole this experiment suggests that very permeable soils are best for growing radishes, which would mean that radishes would prefer less water than what was given to them, as sand drains the best out of the soils used in the experimentation. The heavy humus preference would point to radishes being mineral intensive plants, gaining many minerals and nutrients from organic material, rather than the soil itself. This is further demonstrated by the fact that regardless of soil type, heavy humus grew the highest, but within heavy humus, there was little difference in height based on soil type other than the fact that 100% sand grew the best, and that 75% clay did the worst. However, considering that the 25% sand issue was probably an error within the experiment itself and not actually fully representative of the effect of that soil on radish growth, one can conclude that radishes prefer lower amounts of water, and greater organic material as compared to what was given to them in the experiment. Another small flaw in the experiment is the fact that in the individual soil graphs the height of a plant was sometimes said to go down, as in the plant was shrinking. While this is clearly not possible, there are a number of potential explanations. The first, and probably most likely, is that human error caused a lower number to be written down, or the plant wasn’t measured carefully enough. Alternately, the plant could have wilted overnight, causing it to register a lower height than it actually was. Lastly, the tallest plant may have died, and another would have thus been measured instead. These flaws, while noticeable in individual graphs, make little difference in the two included graphs, as they are based off of averages, not raw data points. When one looks at this data in a more abstract sense, these findings, while not matching the hypothesis, do make sense based off the biology of the radish itself. Radishes grow only in the top 4-6 inches of the topsoil, known as the O-horizon, and do not go any deeper for the most part. This small area of the topsoil has a large amount of organic material [8], which would lead to radishes in theory evolving to take advantage of that over millions of years. Also, this area of the soil is never a part of the water table unless flooding is occurring, meaning that the plants that live exclusively there will on the whole have less water than a plant that reaches into the water table, such as a tree. Therefore, these plants, which include radishes, would be designed to require less water than many other species of plant, and thus when given too much would become waterlogged and drown easier than hardier, deeper-rooted species of plant. Lastly, there could be a flaw in the fact that only the first two weeks of plant growth are documented, leaving the soils affect on the rest of the plants lives untested. However, the type of radish we were using, called cherry belle, only takes 22 days to harvest from germination (4). As the first 6 days were documented, only 27% of the plants lives were documented. However, looking at the first graph, one can see that while the heavy humus plants start out only 6 millimeters ahead of their competitors. But on the third day, the gap had widened to 13 millimeters, and on the sixth and final day the gap had reached 18 millimeters. This constant widening of the gap in heights shows that not only does the heavy humus make the plants grow faster in germination, but it is a continued advantage, spanning for at least a week. The second graph, showing soil type differences, shows that on the first day the sand, which was eventually the most successful, had no discernable advantage over its competitors. But on the third day, the gap had become 6 millimeters. On the sixth day, the gap had grown to 10 millimeters. These findings are similar to the findings in the first graph; that over time the advantage caused accelerated growth, in addition to starting out taller than the other plants. Thus, while the last portion of the plants lives was not studied, it stands to reason that the pattern shown in their early life would continue, and the soils would continue to have a prolonged affect on their growth. Understanding that lots of organic matter is needed, in addition to good drainage, for radishes is important for farmers, as well as home gardeners, to know. With this information, farmers can determine if their soil will support radishes before it’s too late. More importantly though, this information would allow radishes to be grown anywhere in the world where there are high levels of sand in comparison to clay and plentiful organic matter. Radishes are an excellent source of calcium, and are well known for helping regulate blood pressure, helping maintain a healthy gallbladder and liver, and may even help prevent cancer (7). If the precise ideal conditions were known for growing radishes in, hypothetically it could help reduce malnutrition and world hunger. While knowing the ideal soil composition is essential in knowing this ideal environment for radishes, further studies regarding amount of sunlight, temperature, and water received by the plant would be necessary in narrowing down the most prosperous conditions for radishes to grow in. Hence, for this experiment to be thorough, the independent variables would need to be tested, separately, in addition. One very simple way to improve this experiment would be to simply test more plants. This would make averages more powerful tools as they could not be thrown by a few outliers, like some of the ones found in the experiment. Also, rotating the test positions of the plants in this experiment would limit the possibility of one soil being prevented from getting the exact same conditions, as was suspected for the 25% sand soil. Lastly, this could be done in a perfectly temperature and humidity controlled greenhouse or lab, as opposed to a quiet and closed room, for if this experiment were to be done in an even more temperature controlled environment it would prevent tiny fluctuations in air temperature as could happen if a draft were to occur. As for the extended applications of this experiment, it is unadvised to attempt to use this data for other plants, as each species is different, and thus should have different growing conditions. Thus, attempting to apply this data on radishes, a small bulb with a single shallow root, to a tree, a massive deep-rooted plant with a complex leaf and branch structure, would be pointless. The species in question are so different that little could be gleaned about one from studies on the other.
 * Discussion **

** Sources: **

** 1 ** ) Tarbuck, Edward J., and Fredrick K. Lutgens. "Soil." In Earth Science, 133-135. N.p.: Pearson Education Inc., 2009.  **2**) Scherer, Thomas F, Bruce Seelig, and David Franzen. "Soil, Water, and Plant Characteristics Important to Irrigation." North Dakota State University. Last modified 1996. [] eb66w.htm#soil. **3**) Wolford, Ron, and Drusilla Banks. "Beans." Watch Your Garden Grow. [] .  ** 4 ** ) Wolford, Ron, and Drusilla Banks. "Radish." Watch Your Garden Grow. [|h] [|[[http://urbanext.illinois.edu/veggies/radish.cfm|ttp://urbanext.illinois.edu/veggies/radish.cfm.]]] ** 5 ** ) "What is Permeability?" Preface to Ward's Porosity and Permeability of Soil Model, 3. h [|ttp://www.spegcs.org/attachments/committees/8/] Porosity%20Model_Users%20Guide_040607.pdf.  **6**) "Pak Choi Handbook: Crop Health," Controlled Environment Agriculture, h [|ttp://www.cornellcea.com/Pakchoi_Handbook/pc_crop_health.htm.] ** 7 ** ) Gongal, Patricia, and Brett Huffman. "The Health Benefits of Radishes." Elements 4 Health. Last modified April 1, 2008. http://www.elements4health.com/radishes.html.  ** 8) ** Soil Layers." Enchanted Learning. N.p., n.d. Web. 6 June 2011. []