Geoscience Reference
In-Depth Information
Table 15.2
Area distribution of erosion classes by island grouping (in million ha)
Erosion class
Unclassified
*
No apparent
Slight
Moderate
Severe
Totals
Island
grouping
Area
%
Area
%
Area
%
Area
%
Area
%
Area
%
Luzon
4.1
57.7
4.1
46.6
4.1
48.2
1.7
32.7
0.2
50.0
14.2
(47)
Visayas
1.2
16.9
1.7
19.3
1.5
17.0
1.1
21.2
0.1
25.0
5.6
(19)
Mindanao
1.8
25.4
3.0
34.1
2.9
34.1
2.4
46.1
0.1
25.0
10.2
(34)
Philippines
7.1
23.7
8.8
29.4
8.5
28.3
5.2
17.3
0.4
1.3
30.0
(100)
Source: Bureau of Soils and Water Management (1993)
*
Unclassified erosion refers to quarry, river wash, and open pit mines
Other types of soils degradation associated with soil erosion are loss of soil
nutrients and or organic matter, river erosion, flooding and water logging (Fig.
15.3
).
3.2
Soil Mining and Decline of Soil Productivity
The long term and continued use of urea “alone” resulted in serious nutrient
imbalance and contributed to the actual silent soil degradation widely known as
soil mining. The general trend based from soil analysis covering a 20 year period
indicated very active soil mining where there is now an increasing number of plant
nutrients required to sustain plant growth.
4
Causal Factors of Land Degradation
4.1
Natural Causes
4.1.1
Topographic Variations and Problem Soils
The Philippines is an archipelago with topographic variations in its various islands.
It has several mountains/hilly lands present all over the country which are expe-
riencing decreased in land cover, thus, making them more prone to soil erosion.
Furthermore, problem soils are dominant in the Philippines characterized by steep
slopes, poor drainage, coarse textures and fertility limitations.
4.1.2
Volcanic Eruptions
There are more than 200 volcanoes in the country and four major volcanic belts,
namely: the Westerly Convex Volcanic Belt in Luzon, Easterly Convex Volcanic
Belt, Westerly Volcanic Belt and Southeasterly Volcanic Belt.
Search WWH ::
Custom Search