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Soil organic carbon and nitrogen distribution in a tropical watershed
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Abstract
The role of soils in sequestering atmospheric carbon (C) and nitrogen (N) can best
be understood from a watershed perspective because the multiple influences of factors
influencing the process can be assessed simultaneously, within a hydrologic unit. It is
important to identify land uses and management practices that maximize soil carbon
sequestration and help a meliorate the effects of CO2 emissions to the atmosphere. The
spatial distribution and the effects of soil order, land use and soil phase on the total soil
organic carbon (SOC) and soil organic nitrogen (SON) content were assessed in the Río
Grande de Arecibo watershed in Puerto Rico (RGA). A Geographical Information
System (GIS) was used to develop the sampling strategy. Soil samples were taken at five
depth increments (0-15, 15-30, 30-50, 50-75, 75-100 cm) from 21 soil series under
diverse land use types within the watershed. Spatial distribution maps of SOC and SON
according to mapping units, soil orders and land use types were generated. The mapping
unit area-weighted mean SOC content was 4.15 kg C m-2 and 10.9 kg C m-2 in the 0-15
cm and 0-100 cm depths, respectively. In general, the soils sampled in the watershed
(33,322 ha or 84% of the total land area) contain 3.98 x 106 Mg of organic C and 0.38 x
106
Mg of organic N to depth from 0 to 100 cm. The area-weighted mean SON content
was 0.372 kg N m-2 and 1.05 kg N m-2 for the 0-15 and 0-100 cm, depths respectively.
Forest and pasture soils contained higher amounts of SOC (12.8 and 9.79 kg C m2
,
respectively) (P<0.05) than soils under cultivation (7.90 kg C m-2) for the 0-100 cm
depths. The SOC was significantly different (P<0.05) among soil orders in the 0-15cm
depth (Oxisols and Ultisols > Inceptisols) and in the 0-100 cm depth (Oxisols > Ultisols >
Inceptisols). These results allow a better understanding of the impacts of land use on soil
C and N stocks at the watershed level.
Description
Date
2004
Journal Title
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Keywords
Atmospheric carbon, Cultivation