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This report is examining the effects that plants growing in overcrowded conditions go through and what affects overcrowding has on seedlings making comparisons to plants which have been grown in normal/ideal special conditions. It also includes literature research into the different methods which are used for the growth of plants in both commercial settings and private setting and which method suits this investigation s purposes best. It gives results in both observational and quantitative ways and explains/gives definitions for words that may not have been understood.
This is an investigation to discover what happens to a plant population of germinating seeds that are grown in overcrowded conditions compared to the germination of seeds that are grown in an area where they are sufficient nutrients, space and light.
Germination the beginning of growth for a seed , the beginnings of a new plant 1
Loam soil soil composed of sand, silt, and clay in relatively even concentration. Loam soils generally contain more nutrients and humus than sandy soils, have better infiltration and drainage than silty soils, and are easier to till than clay soils. Loams are gritty, moist, and retain water easily. 2
Horticulture the industry and science of plant cultivation including the process of preparing soil for the planting of seeds, tubers, or cuttings. 3
Overcrowding when the number of organisms exceed the carrying capacity of an area (in this investigation it will be the soil) 4
Vermiculite any of a group micaceous hydrated silicate minerals related to the chlorites and used in heat-expanded form as insulation and as a planting medium. 5
Hydroponics the cultivation of plants in a nutrient-rich solution, rather than in soil, and under controlled conditions of light, temperature, and humidity. Also called aquaculture. 6
Ideal germination conditions for 3 plant species:
1. Radish (Raphanus sativus) sandy loam soil that has been tilled is ideal for germination and growth, seeds need to be planted at the write depth for the seed to germinate properly, 1cm for small radishes and 4cm for large radishes. Will germinate between 3 and 7 days and is ready for harvesting in about 4 weeks.
2. Pea (Pisum sativum) soak the seed in water for about 4 hours before planting it, plant the seeds in rows. The seeds should be planted about 2cm deep between 6 -8 cm apart. Water them daily as they require lots and use organic mulch.
3. California poppy (Eschscholzia californica) sow in soil that is in full sun, these poppies like soil that is of a poor soil condition. Sow directly onto the soil and then dig the seeds in and add water and germination will begin within a few days.
Germination methods used by horticulturalists
Method Pro s Con s
Growth in cotton wool Can observe the germination process easily The roots become entangled in the cotton wool and it may become difficult to remove the seed from the cotton wool
Growth in vermiculite Adds nutrients to the plants environment
Holds water very well so that plants don t experience a shortage Research shows no disadvantages
Hydroponics No soil is needed
Nutrient levels in the water are control for each type of plant
Stable and large yields of plants
No major pest problems Plants may become infected with Verticillium wilt due to the high moisture levels
Water and nutrient costs may be expensive
Evidence and measurement of growth in plants:
Measuring the space between the internodes of along the stem of the plant
Measuring the size of the leaves, by measuring the length of the leaves along its mid vein to the node where it connects to the stem
Counting the number of leaves on the plant
Checking the weight of the plant (will not be used in this investigation as it requires a large number of plants and will result in plants being removed from the soil so that they can be weighted, this will most likely result in the death of the plant.).
Possible effects of overcrowding:
Radish size of the root (part which is harvested) will be greatly reduced, size of the leaves will be small and few leaves will be present, very tall stems.
Pea reduced size and number of leaves, flowering rate will be reduced, pods will be greatly reduced in size
California poppy lives very well in malnourished soil and in overcrowded conditions
How may overcrowding be overcome by the plant?
Will grow tall thin stems and try to grow higher than other plants, roots system will be very small. Stems as a result of being tall and thin are unable to support the weight of the leaves and the plant collapses. Horticulturalists solve the problem of overcrowding by providing the plants with sufficient resources that they require for grow. They also remove the plants from the greenhouses before them become too big. If overcrowding does occur they separate the plants and give them sufficient space, they will also dispose of any weak plants that will not grow properly.
Hypothesis: The overcrowded plants will develop weak stems and their growth rates will be hampered due to lack of nutrients.
To investigate the effects of overcrowding on germinating seeds and the effects of overcrowding on the growth of seedlings.
Independent variable the number of radish seeds planted in each seedling tray.
Dependent variable the growth of the plants in terms of their stem length and size of their leaves.
Fixed variables the size of the seedlings trays must be the same size, the amount of soil placed in the seedling trays is filled to the same point, the amount of water given to each seedling tray must be equal in this case 500ml every 2nd day.
Two seedling trays
Fill two equally sized seedling trays with sand to the same point.
Moisten the soil and prepare it for planting the seeds.
Using Radish seeds, plant 9 seeds in the 1st tray using the conditions indicated on the back of the seeds packaging then in the 2nd tray plant at least 45 seeds in close proximity to each other.
Once seeds have been planted place the trays in a hot house
Once germination has taken place and the plants have begun growing out of the soil measure the length of the stem and the length of the mid-vein in the leaves every 4 days.
Measure the growth of the plants over a period of 40 days
Seeds were plant the 26th January 2011
After 2 days the soil began to lift in the overcrowded tray
On the 3rd day the seedling were beginning to emerge from the soil in the overcrowded tray
On the 5th day the seedling in the ideal conditions tray began to emerge from the soil
The overcrowded seedlings grew at a very fast rate in comparison to the ideal conditions seedling
The growth rate of the overcrowded population plants slowed down where as the ideal conditions population plants grew at a steady rate
On the night of the 15th of February 2011 the majority of the ideal conditions plant population s and some the overcrowded plants population s where eaten, possibly by slugs
Seedling trays were removed from the hot house so that they remain plants would survive and so the damaged ones could recover
Damaged plant s stems began to shrink as the secondary leaves were getting ready to grow, once the secondary leaves had begun to grow larger and the plants were receiving food from being able to photosynthesis again, the stems began growing taller again
In the overcrowded tray the smaller plants stopped growing and the larger plants began to go limp as their stems became too long and too thin to support the weight of the leaves
Some of the overcrowded plants began to experience their leaves going yellow and the plants starting to die off due to lack of resources
See appendix figure 4 for picture of leaves yellowing
For tables of results see appendix
The length of the leaves in the ideal conditions plant population on the 16th day was so low compared to the leaves length on the 12th day due to the leaves having been eaten two days earlier by suspected to be slugs.
The greater growth rate experienced in the overcrowded plant population in the first few days was most likely caused by chemical released by the seeds to encourage growth and as they are in such close proximity and there are so many it may cause them to have an overload of the chemical resulting the extremely fast initial growth rate.
The overcrowded plants grew at faster rate than that of the ideal conditions plants yet the overcrowded plants became weak very quickly and as a result weaker plants remained small or died and taller plants grew flimsy. The ideal plants grew to be stronger and healthier plants despite that they were partially eaten.