Page 172 - Ilmu Tanah

The Chemistry and Fertility of Soils under Tropical Weeds 159

Key Questions

1. How does the soil acidification occur by weed rooting system? What substances and
reactions involved in this process? Explain!
2. How does the oxidation reaction in the weed roots producing CO 2 occur and acidify the
soils? Explain!
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3. What are the effects of root excretion of H and organic acids? What soil properties are
affected by the these substances? Explain!
4. One way of weeds to extract soil nutrients is by excreting enzymes through their roots.
Explain the mechanism!
5. What are the functions of enzymes? Explain it with examples! What is the relationship
of this reaction with the soil organic and inorganic sources of soil nutrients?
6. Explain the role of soil enzymes in the nutrient cycles including the C-, N-, S-, and P
cycles!
7. Explain the effect of weeds on soil physical properties with some examples! Explain the
particular effect of weeds on soil moisture content!
8. Explain the effect of weeds on soil chemical properties with some examples! Explain
the particular effect of weeds on soil K!
9. Explain the effect of weeds on soil biological properties with some examples! Explain
the particular effect of weeds on soil bacterial and fungal population and activities!
10. Explain the effect of weeds on soil pH with some chemical reactions!
11. Explain the effect of weeds on the availabilities of some plant nutrients! Explain the
particular effect of weeds on soil total N!
12. Explain the effect of weeds on soil cation exchange capacity (CEC)! What soil properties
directly affect this? Does weed roots affect these soil properties?
13. Explain the effects of weeds on soil organic C and organic matter content!
14. Explain the effects of weeds on soil heavy metal availabilities! What soil properties
directly affect this? Do weed roots affect these soil properties? Explain! Explain the
particular effect of weed on soil Pb!
15. Can the presence of weeds affect the soil mineral weathering? Explain what soil
properties may accelerate this reaction and how! How do weeds affect the changes in
these soil properties? Explain!
16. How do weeds accelerate the soil organic matter decomposition? What soil properties
affect this reaction? How do weeds affect the changes in these soil properties? Explain!
17. The increase in soil CEC may increase the soil mineral weathering dan organic matter
decomposition. How do weeds involve in this acceleration? What chemical reactions
involved in this process?

Abdul Kadir Salam and Nanik Sriyani – 2019