Review+Questions+-+3+Key - Soil Science 10 Fall 2010 REVIEW...

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Soil Science 10 Fall 2010 REVIEW QUESTIONS # 3 1. What important roles do soil macro animals play in soil systems? (T14) i) breakdown organic matter particle size, ii) increase aeration (biopores), iii) mix & granulate soil, iv) create and improve stability of soil structure. 2. What roles do soil micro organisms play in the soil? Are all these roles beneficial? (T14) i) decomposition/mineralization, ii) humus formation, iii) improve soil physical properties, iv) chelates, v) fix nitrogen gas, vi) mycorrhizae improve water & nutrient acquisition, vii) keep bad organisms in check, viii) breakdown toxic chemicals (bioremediation). BAD: i) plant disease, ii) denitrification, iii) compete for nutrients. 3. What is the difference between a heterotroph and an autotroph? What is the difference between anaerobic, aerobic, and facultative bacteria? (T14) Heterotrophs – require soil organic matter for energy. Autotrophs – fix their own carbon with energy from sun or oxidation of elements. Anaerobic – no oxygen (O 2 is toxic). Aerobic – require oxygen. Faculative – can live with or without oxygen. 4. What is a symbiotic relationship? (T14) Two dissimilar organisms living together in intimate association, the cohabitation being mutually beneficial - mycorrhizae fungi and plant roots. 5. Why are plants willing to give up photosynthate (food) to mycorrhizae that infect their roots? (T14) The plant receives more nutrients, water and pathogen protection due to the activities of the fungi (chelates and increased rooting surface area increase nutrient and water uptake; antibiotic production protects from pathogens). 6. What are the optimum conditions of temperature, moisture, oxygen, pH, exchangeable Ca, and C/N ratio for organic matter decomposition by aerobic bacteria? (T14) Temperature – generally 20-40 o C; moisture – near field capacity; oxygen – as much as possible; pH=6-8; exchangeable Ca – high; C/N<30 7. What is nitrogen fixation? What is denitrification? What types of organisms are responsible for these processes? (T14) N fixation is taking N 2 gas from the atmosphere and converting it to ammonium (NH 4 ) that is available for plant nutrition – aerobic bacteria perform N 2 fixation. Denitrification is conversion of nitrate to nitrogen gas (NO 3 N 2 gas) – performed by anaerobic bacteria. 8. What is an essential plant nutrient? Can a plant grow at all if it is missing a particular essential nutrient? (T15) Nutrients required by a plant to complete it’s life cycle ( i.e., reproduce); plants can sometimes grow without certain essential nutrients but they will not reproduce.
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9. How many essential elements are required by most plants? What is ultimate source of each nutrient? (T15)
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Review+Questions+-+3+Key - Soil Science 10 Fall 2010 REVIEW...

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