Presentation on theme: "Nitrogen in Soil and the Nitrogen Cycle. What Is Nitrogen? Chemical Element, commonly a colorless, tasteless, odorless gas. 78 % by volume of the Earth’s."— Presentation transcript:
What Is Nitrogen? Chemical Element, commonly a colorless, tasteless, odorless gas. 78 % by volume of the Earth’s Atmosphere.
Plants and animals need nitrogen. Plants and animals need nitrogen for DNA, RNA and proteins. Nitrogen is part of chlorophyll molecules in plants.
Relevant forms of nitrogen Nitrogen gas: N 2 Nitrate ions: NO 3 -1 Nitrite ions: NO 2 -1 Ammonium ions: NH 4 +1 Nitrous oxide (laughing gas) N 2 O
Bacteria drive the nitrogen cycle Bacteria need to convert nitrogen gas from the air into usable forms: nitrate and ammonium for plants! Bacteria and fungi decompose plants and animals, producing nitrogen compounds in the soil. Plants absorb nitrate and ammonium through their roots and assimilate these compounds into their structures. Animals eat plants and other animals to gain nitrogen.
Vocabulary Nitrogen Fixation: Some living organisms (rhizobium bacteria in legumes) can convert nitrogen into useful compounds such as ammonia. Lightning also takes a part in nitrogen fixation. Ammonification: Decomposition of detritus (dead plants, animals) by bacteria produces ammonia and ammonium compounds in soil. Nitrification: Nitrifying bacteria convert ammonium to nitrite (toxic to plants) and nitrate. Denitrification: Anaerobic bacteria convert nitrate, nitrite, ammonium into nitrous oxide and nitrogen in the air in swamps and wetlands. This reduces soil nitrogen.
Nitrogen Fixation: Some living organisms (Legumes or certain bacteria) can convert nitrogen into ammonia, NH 3. Cyanobacteria, rhizobium bacteria and other bacteria fix nitrogen from the air and convert it into ammonia.
Rhisomes = root nodules on legumes contain rhizobmium. bacteria.
A study of nitrogen fixation by alder trees. Alders were planted with Douglas Fir in the 1930’s after a fire. This photo was taken in 1990. The dark green band containing alder trees have nitrogen fixing bacteria that grow with it.
Sources of Nitrogen for Plant Growth Nitrogen gas in the atmosphere, which must be converted into nitrate or ammonium by bacteria Commercial Fertilizers Soil Organic Matter Crop Residues (leaves and stalks from plants) Animal Manures
Commercial Fertilizers: add ammonium and nitrate to soils
Chemical Fertilizers Haber Process used to make synthetic fertilizers Advantage: Crop yields increase Disadvantage: Agricultural runoff pollutes lakes and rivers with fertilizers, causing algal blooms.
Questions 1.What is the most abundant gas in the atmosphere? 2.What forms of nitrogen are useful to plants? 3.What kinds of plants fix nitrogen? 4.What is a rhizome? 5.How does adding manure to the soil increase nitrogen in the soil? 6.What is nitrification? 7.Why are bacteria important for the nitrogen cycle?
More questions 1.Why are wet soils low in nitrogen? 2.Why do farmers add nitrogen to the soil? 3.What is the impact of agricultural runoff on lakes and rivers? 4.What is an algal bloom? 5.What is the dead zone? 6.Why is composting a good idea?