1. Agriculture and Nutrient Cycles Chapter 2.7

2. Agriculture and Nutrient Cycles The seeds, leaves, flowers and fruits of plants all contain valuable nutrients. As crops are harvested, the valuable nitrogen and phosphorus are removed and do not return to the field. This diversion of nitrates and phosphate from the local cycles would soon deplete the soil unless the farmer replaced the missing nutrients.

3. There are many other elements/nutrients that plants need, other than carbon. The most important other nutrients are nitrogen (N), phosphorus (P), and potassium (K) As plants grow, they remove these nutrients from the soil. FERTILIZERSFERTILIZERS are materials used to restore nutrients and increase production from land.

4. However, adding too much fertilizer is not always better. Extra, unused fertilizer can end up in streams and lakes.

5. Fertilizer and Ecosystems Read the first paragraph of “Fertilizer and ecosystems” on page 70 ( 10 minutes ) Question What can happen to organisms when too much fertilizer is used? Answer: Nutrients allow algae to grow rapidly ( algal bloom) Algae die – Bacteria uses oxygen – oxygen levels drop – fish / other animals die – decomposer eat – bacteria population grows – use more oxygen.

6. Class Questions ( 20 minutes) Answer questions Page 71 #1,2,4,5

7. SOLUTIONS TO QUESTIONS Q1 – Why do the levels of nitrogen and phosphorus in fields decline when crops are harvested? Answer: Because some of these nutrients are taken away in the crop

8. SOLUTIONS TO QUESTIONS Q2 – Explain how excess fertilizers might affect decomposing organisms. ANSWER: Excess fertilizer can seep into waterways and cause the growth of algae. When the algae die, the population of decomposers increases rapidly, causing oxygen depletion in the water.

9. SOLUTIONS TO QUESTIONS Q4 – What dangers do high levels of nitrates in the drinking water present for infants? ANSWER: Their stomachs are not as acidic as those of adults. Bacteria that convert nitrates to nitrites in the intestines can enter infants’ less acidic stomachs. The nitrites can enter the blood stream and bind to the hemoglobin.

10. SOLUTIONS TO QUESTIONS Q5 – Explain why not planting a crop and then ploughing in the fall might help a framer restore nitrogen and phosphorus levels in the soil. ANSWER: During the year nutrients, including nitrogen and phosphorous, accumulate in the plants that grow. If the farmer ploughs these plants under in the fall, the nutrients will help enrich the soil. This is called “green manure.”