| MadSci Network: Botany |
Complete Question: Hello! My Biology Class assigned us to create a lab experiment with plants. My experiment will have soil as the variable. I will have 3 pots, one pot with just regular soil, another pot of soil without nitrogen (I'm going to burn off the nitrates and wash it out), and the last pot containing nitrogen-enriched soil. So I was just wondering how I can regulate the amount of nitrogen I can put into the third pot of soil? Thanks~! Reply: I don't recommend trying to "burn off nitrates" because heat treating a soil can cause manganese toxicity problems plus you need to burn off all the organic matter as well because the main supply of nitrogen in soil is in the organic matter. Burning off organic matter requires extremely high temperatures, (a few hundred degrees Celsius) and requires a fume hood, a Meeker burner, and safety procedures. Soil organic matter slowly releases nitrogen to the plant. You could use the same potting soil and then irrigate with tap water as a control and two or more different strengths of a fertilizer solution, such as Miracle-Gro. That would vary all the mineral nutrients in Miracle-Gro but would be easiest to set up. If you want to vary just nitrogen and keep the other mineral nutrients realtively constant, you would need to make nutrient solutions, such as a Hoagland solution with normal nitrogen, zero nitrogen and maybe 10% of normal nitrogen. You could irrigate the potted plants with the Hoagland solutions. Alternately, you could not use soil at all and grow the plants in solution culture hydroponics. Regardless of your approach, try to have adequate replication, preferably five plants or five pots for each treatment. Hoagland solution recipes: Hoagland solution #1 (per liter of nutrient solution): 5 ml of 1 M (M=Molar) potassium nitrate 5 ml of 1 M calcium nitrate 1 ml of 1 M monopotassium phosphate 2 ml of 1 M magnesium sulfate 1 ml of micronutrient stock solution (see recipe below) 1 to 5 ml of 1000 mg/liter iron from iron chelate (Fe-EDTA, Fe-DTPA, or Fe-EDDHA) Hoagland Solution minus nitrogen (per liter of nutrient solution): 10 ml of 0.05 M monocalcium phosphate 200 ml of 0.01 M calcium sulfate dihydrate 5 ml of 0.5 M potassium sulfate 2 ml of 1 M magnesium sulfate 1 ml of micronutrient stock solution 1 to 5 ml of iron chelate stock solution as for #1 (add some calcium nitrate to give a Hoagland solution with some nitrogen but less than 100% nitrogen, e.g. 10% nitrogen is supplied by 0.75 ml of 1 Molar calcium nitrate) Micronutrient stock solution per liter: 2.86 g boric acid 1.81 g manganese chloride - 4 hydrate 0.22 g zinc sulfate - 7 hydrate 0.08 g copper sulfate - 5 hydrate 0.02 g 85% molybdic acid When diluted 1:1000 the micronutrient stock solution provides the following in mg/liter: Boron 0.5 Manganese 0.5 Zinc 0.05 Copper 0.02 Molybdenum 0.01 References Hershey, D.R. 1995. Plant Biology Science Projects. New York: Wiley. Hershey, D.R. 1994. Solution culture hydroponics: History and inexpensive equipment. American Biology Teacher 56: 111-118.
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