Quantification and valuation of soil erosion in various landuses in Manupali watershed
1999
Gadrinab, A.B.
The study mainly aimed at quantifying and costing soil erosion by replacement method in Manupali watershed. The role of forest in controlling erosion and sustaining land productivity is shown by its very low erosion and very high inherent soil fertility. This is despite the fact that forests are located in the highlands where rainfall is higher, winds stronger, slopes steeper, and soils more erodible. When forests are opened, as when they are converted into agriculture, land degradation follows. Between 1981 and 1999, soil losses, in tons/ha/yr, accelerated from 319 to 393. NPK losses also increased, in kg/ha/yr, from 933 to 1027 N, 124 to 145 P, and 1419 to 1617 K. Land degradation followed as shown by the decreasing NPK content of soil, in kg/ha-cm, from 317 to 285 N, 42 to 40 P, and 483 to 448 K. Replacement cost per ha/yr, increased from P29,957 to 33,677 during the same period due to accelerated erosion. Farming steep-lands, despite farming technology, only aggravates erosion. Average soil loss at farm level at 744 tons/ha/yr is 189 percent higher than the watershed level. However, replacement cost per ha/yr is only P25,888 which is 23 percent lower than the watershed level. This indicates that high soil losses do not always translate into high nutrient losses or erosion costs especially for farms sited in highly eroded lands. This study shows that land quality in the watershed declines due to increasing soil and nutrient losses, and decreasing inherent soil fertility. Haphazard rehabilitation of steeplands only worsens land degradation of the watershed
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