1. Agriculture and Nutrient Cycles Lesson 7 December 6, 2010

2. All plants contain valuable nutrients When crops are harvested to be used as food for us, the valuable nitrogen and phosphorous are removed The nitrogen and phosphorous do not return to the field or orchard

3. The elimination of nitrogen and phosphorous from the cycles would soon deplete the soil of the nutrients Farmers replace the missing nutrients with fertilizer Fertilizer-materials used to restore nutrients and increase production from land. Fertilizer containing nitrogen and phosphorous can double the amount of cereal crops (like wheat and barley) BUT, more is not necessarily better

4. Soil bacteria convert nitrogen to nitrates High levels of nitrates increases the amount of nitric acids in the soil Changes in acidity can affect all organisms living in the soil, including decomposers A change of just one pH level can be devastating for some crops Prairies- drop of 1 alfalfa and barley Great Lakes- drop of 2 almost all commercial crops

5. Fertilizer and Ecosystems Nitrogen and phosphorous fertilizers can produce an environmental problem Spring run-off carries decaying plant matter and fertilized soil to streams and then lakes Nutrients allow algae to grow more rapidly

6. When algae die, bacteria use oxygen from water to decompose them Decomposers flourish due to high food availability, therefore taking up more of the water’s oxygen Fish and other animals die due to the low oxygen levels The dying animals make the problem worse because the decomposers recycle the matter from the dead animal, allowing more bacteria to grow and use even more oxygen

7. Nitrates are another problem Bacteria convert nitrates into nitrites Nitrites are dangerous to animals that have hemoglobin in their blood. Nitrites attach to hemoglobin, reducing its ability to carry oxygen to body tissues

8. Nitrites in water is most harmful to young animals- that includes baby humans Most animals have a bacteria in their large intestines that convert nitrites into nitrates In adults, these bacteria are not harmful because stomachs are so acidic that the bacteria cannot survive

9. However, in babies, the stomach is much less acidic and the bacteria travels up into the stomach allowing nitrates to be converted into nitrites The nitrites are then passed into the blood of the infant

10. Case Study 2.8 Effects of Deforestation on Cycling

11. Try This Activity on page 71