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Soil pH and Nutrient Testing for Garden Applications
Through this experiment, you learn about the pH and nutrient content of various soil types. Soil testing kits for pH, nitrogen, phosphorus and potassium are readily available through nurseries and home improvement stores. Use samples of several different types of soil such as sand, silt, clay and loam for the experiment. Conduct the experiment by using a sample of each soil type and the testing kits to determine the pH, nitrogen, phosphorus and potassium levels in each sample. Compare the results of the tests from each soil type to observe differences and similarities in the soil properties. You can also use samples of similar soil types from different locations to evaluate if the surroundings influence pH and nutrient levels.
Best Type of Soil for Plant Growth
This experiment will allow you to determine which soil type is best for growing a specific plant type. Choose a shrub or flower type for the experiment and purchase several similar plants or use seeds. Place the plants or seeds in pots, each with a different soil type. Keep the initial plant and pot size the same. Additionally, you should give each plant the same amount of water, sunlight and fertilizer so that the only variable in the experiment is the soil type. Observe the plants over several months to determine which soil type helped the plant grow the most.
Particle Size Differences in Soil Types
Soil types are defined by their particle size. Clay particles are less than 0.002 mm in size and silt ranges from 0.002 mm to 0.074 mm. Sand particles range from 0.075 mm to 4.75 mm while larger particles are gravels, boulders and cobbles. Soil may have a single particle size or it may be a mixture. To understand the differences in particle sizes, you can use a sieve analysis using a Number 200 and Number 4 sieve. Pour various soil samples through the sieves beginning with Number 4 and then the Number 200. The Number 4 sieve has 4.76 mm openings therefore, it will hold gravel, boulders and cobbles while sand, silt and clay will pass through. The Number 200 sieve has 0.74 mm openings and will retain sand but allow silt and clay to pass through. Silt and clay are both too small to see individual grains; however, the silt will feel slightly gritty between your fingers. Weigh the amount of each particle size in the soil samples to understand if the samples are mostly a single particle type or if they were a mixture.
Water Absorption Testing
Soil scientists perform percolation tests to determine the rate that water is absorbed by and passes through the soil. Standard percolation tests require that you dig several deep holes in the ground; however, you can perform a modified test in a classroom or at home to observe similar results. To conduct this test, you can use kitchen strainers or a plastic cups with holes in the bottom lined with a coffee filter. The filter will retain the soil particles while allowing water to pass through. Fill the containers with different soil types such as clean sand, silt, clay and loam. Pour the same amount of liquid in each container and time how long it takes the water to seep into the top of the soil and how quickly is passes through the soil and exits the bottom of the container. Measure the volume of the water that comes out of the container and compare it to the amount that you poured onto the top to determine how much water is retained in the soil. Compare the results of each soil test to observe which soil absorbs the most and which transmits the water fastest.