- Soil
erosion can cause on-site and off-site damages.
On-site, damages can be in the form of reduced crop yield,
reduced soil depth or lower soil nutrient content.
Offsite damages can be in the form of water pollution,
reduced irrigation capacity, flooding, foregone
productivity of fishery, hydropower, and agricultural
systems.
- The
average rate of soil lost due to erosion ranges from
1t/ha/yr for areas planted with grasses and trees to 268
t/ha/yr for cultivated areas. On-site damages due to lost
soil nutrients have been estimated at
P2,711
per hectare. Estimates also show that off-site losses due
to reduced capacity of irrigation and hydropower could
reach P460,800 for an upland area of 100
ha with vegetative cover (NRAP-Phase I Main Report, 1992).
- The
environment, specifically bodies of water, acts as
receptor of pollutants associated with runoff. These
pollutants can be in the form of Biochemical Oxygen Demand
5 (BOD5), and Suspended sediments (SS). Total
agricultural crop production in 1992 is estimated to
contribute 770,249 mt and 152,858,963 mt, respectively (ENRAP-Phase
III Main Report, 1996). The value of surface runoff
due to agricultural production is computed at P2.57B in
1992 based on 1988 Agricultural Ecosystemss (ENRAP-Phase
III Main Report, 1996)
-
Pollutants from agricultural runoff can
also come from organic wastes, which include decayed plants
and leaves, livestock manure and dead insects or animals
left to rot in the fields.
-
Other sources of pollutants are
pesticides and fertilizer residues.
-
Adopting soil and water conservation
practices can reduce the amount of damages due to erosion.
It is estimated that even with partial adoption (10-20%),
damage due to erosion can be reduced by P271 – 542 per ha
per year on-site.
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