Page 65 - Ilmu Tanah Book

52 The Chemistry and Fertility of Soils under Tropical Weeds

the negative effects of herbicides are minimized and also limit the soil erosion
particularly during rainy seasons (Sriyani, 2010).

Key Questions

1. What are the negative effects of weeds on crop production and farmer’s profit?
Explain!
2. What is allelopathy and how does it affect the production of crop plants? Explain!
3. How does the presence of weeds directly or indirectly pollute the soil and water
environment?
4. How do weeds disturb the natural ecosystem?
5. What characteristics of weeds may determine their ability to invade and displace
indigenous plants?
6. Why does alang-alang quickly grow, propagate, and dominate the new ecosystems?
7. Explain the weed-root excretion and its effect on the soil properties! Give some
examples!
8. Explain the effects of weeds on human and animal health! Give some examples of this
phenomenon!
9. What is the definition of weeds and explain how it is developed! What factors mostly
influence the definition?
10. Explain why weeds are so progressive and invasive? What characteristics causing this
characteristic? Explain!
11. Why are C-4 plants, like most weeds, very competitive? Explain! What are the
consequences?
12. Why weeds are considered an important component in an ecosystem? Explain! How is
role and position of weeds among the vegetation in an ecosystem?
13. Explain plant succession! Why and how does succession occur in the ecosystem?
14. Why do weeds in general become pioneer plants? Explain!
15. What is biological invasion? How does it happen in an ecosystem? Explain!
16. Explain the effects of weed presence on soil erosion and the changes in some soil
chemical properties like organic C, pH, and CEC!
17. How does alang-alang affect the soil pH and enzymatic activities?
18. Why do weeds act as biomass producers in the environment? Explain!
19. What are the difference between weed management and weed control? Which one is
more important?
20. Explain the superiorities and the drawbacks of the methods of weed controls:
preventive, culture technique, mechanical-physical, biocontrol, chemical, and
integrated!

Abdul Kadir Salam and Nanik Sriyani – 2019